diff --git a/en_US.ISO8859-1/books/handbook/security/chapter.sgml b/en_US.ISO8859-1/books/handbook/security/chapter.sgml index f13ba66626..026acfe72a 100644 --- a/en_US.ISO8859-1/books/handbook/security/chapter.sgml +++ b/en_US.ISO8859-1/books/handbook/security/chapter.sgml @@ -1,3478 +1,3478 @@ Matthew Dillon Much of this chapter has been taken from the security(7) manual page by Security security Synopsis This chapter will provide a basic introduction to system security concepts, some general good rules of thumb, and some advanced topics under FreeBSD. A lot of the topics covered here can be applied to system and Internet security in general as well. The Internet is no longer a friendly place in which everyone wants to be your kind neighbor. Securing your system is imperative to protect your data, intellectual property, time, and much more from the hands of hackers and the like. FreeBSD provides an array of utilities and mechanisms to ensure the integrity and security of your system and network. After reading this chapter, you will know: Basic system security concepts, in respect to FreeBSD. About the various crypt mechanisms available in FreeBSD, such as DES and MD5. How to setup S/Key, an alternative, one-time password authentication system. How to setup Kerberos, another alternative authentication system. How to create firewalls using IPFW. How to configure IPsec. How to configure and use OpenSSH, FreeBSD's SSH implementation. Before reading this chapter, you should: Understand basic FreeBSD and Internet concepts. Introduction Security is a function that begins and ends with the system administrator. While all BSD Unix multi-user systems have some inherent security, the job of building and maintaining additional security mechanisms to keep those users honest is probably one of the single largest undertakings of the sysadmin. Machines are only as secure as you make them, and security concerns are ever competing with the human necessity for convenience. Unix systems, in general, are capable of running a huge number of simultaneous processes and many of these processes operate as servers – meaning that external entities can connect and talk to them. As yesterday's mini-computers and mainframes become today's desktops, and as computers become networked and internetworked, security becomes an even bigger issue. Security is best implemented through a layered onion approach. In a nutshell, what you want to do is to create as many layers of security as are convenient and then carefully monitor the system for intrusions. You do not want to overbuild your security or you will interfere with the detection side, and detection is one of the single most important aspects of any security mechanism. For example, it makes little sense to set the schg flags (see &man.chflags.1;) on every system binary because while this may temporarily protect the binaries, it prevents an attacker who has broken in from making an easily detectable change that may result in your security mechanisms not detecting the attacker at all. System security also pertains to dealing with various forms of attack, including attacks that attempt to crash, or otherwise make a system unusable, but do not attempt to compromise the root account (break root). Security concerns can be split up into several categories: Denial of service attacks. User account compromises. Root compromise through accessible servers. Root compromise via user accounts. Backdoor creation. DoS attacks Denial of Service (DoS) security DoS attacks Denial of Service (DoS) Denial of Service (DoS) A denial of service attack is an action that deprives the machine of needed resources. Typically, DoS attacks are brute-force mechanisms that attempt to crash or otherwise make a machine unusable by overwhelming its servers or network stack. Some DoS attacks try to take advantage of bugs in the networking stack to crash a machine with a single packet. The latter can only be fixed by applying a bug fix to the kernel. Attacks on servers can often be fixed by properly specifying options to limit the load the servers incur on the system under adverse conditions. Brute-force network attacks are harder to deal with. A spoofed-packet attack, for example, is nearly impossible to stop, short of cutting your system off from the Internet. It may not be able to take your machine down, but it can saturate your Internet connection. security account compromises A user account compromise is even more common than a DoS attack. Many sysadmins still run standard telnetd, rlogind, rshd, and ftpd servers on their machines. These servers, by default, do not operate over encrypted connections. The result is that if you have any moderate-sized user base, one or more of your users logging into your system from a remote location (which is the most common and convenient way to login to a system) will have his or her password sniffed. The attentive system admin will analyze his remote access logs looking for suspicious source addresses even for successful logins. One must always assume that once an attacker has access to a user account, the attacker can break root. However, the reality is that in a well secured and maintained system, access to a user account does not necessarily give the attacker access to root. The distinction is important because without access to root the attacker cannot generally hide his tracks and may, at best, be able to do nothing more than mess with the user's files, or crash the machine. User account compromises are very common because users tend not to take the precautions that sysadmins take. security backdoors System administrators must keep in mind that there are potentially many ways to break root on a machine. The attacker may know the root password, the attacker may find a bug in a root-run server and be able to break root over a network connection to that server, or the attacker may know of a bug in a suid-root program that allows the attacker to break root once he has broken into a user's account. If an attacker has found a way to break root on a machine, the attacker may not have a need to install a backdoor. Many of the root holes found and closed to date involve a considerable amount of work by the attacker to cleanup after himself, so most attackers install backdoors. A backdoor provides the attacker with a way to easily regain root access to the system, but it also gives the smart system administrator a convenient way to detect the intrusion. Making it impossible for an attacker to install a backdoor may actually be detrimental to your security, because it will not close off the hole the attacker found to break in the first place. Security remedies should always be implemented with a multi-layered onion peel approach and can be categorized as follows: Securing root and staff accounts. Securing root – root-run servers and suid/sgid binaries. Securing user accounts. Securing the password file. Securing the kernel core, raw devices, and filesystems. Quick detection of inappropriate changes made to the system. Paranoia. The next section of this chapter will cover the above bullet items in greater depth. security securing Securing FreeBSD Command vs. Protocol Throughout this document, we will use bold text to refer to a command or application. This is used for instances such as ssh, since it is a protocol as well as command. The sections that follow will cover the methods of securing your FreeBSD system that were mentioned in the last section of this chapter. Securing the <username>root</username> Account and Staff Accounts su First off, do not bother securing staff accounts if you have not secured the root account. Most systems have a password assigned to the root account. The first thing you do is assume that the password is always compromised. This does not mean that you should remove the password. The password is almost always necessary for console access to the machine. What it does mean is that you should not make it possible to use the password outside of the console or possibly even with the &man.su.1; command. For example, make sure that your pty's are specified as being insecure in the /etc/ttys file so that direct root logins via telnet or rlogin are disallowed. If using other login services such as sshd, make sure that direct root logins are disabled there as well. You can do this by editing your /etc/ssh/sshd_config file, and making sure that PermitRootLogin is set to NO. Consider every access method – services such as FTP often fall through the cracks. Direct root logins should only be allowed via the system console. wheel Of course, as a sysadmin you have to be able to get to root, so we open up a few holes. But we make sure these holes require additional password verification to operate. One way to make root accessible is to add appropriate staff accounts to the wheel group (in /etc/group). The staff members placed in the wheel group are allowed to su to root. You should never give staff members native wheel access by putting them in the wheel group in their password entry. Staff accounts should be placed in a staff group, and then added to the wheel group via the /etc/group file. Only those staff members who actually need to have root access should be placed in the wheel group. It is also possible, when using an authentication method such as Kerberos, to use Kerberos' .k5login file in the root account to allow a &man.ksu.1; to root without having to place anyone at all in the wheel group. This may be the better solution since the wheel mechanism still allows an intruder to break root if the intruder has gotten hold of your password file and can break into a staff account. While having the wheel mechanism is better than having nothing at all, it is not necessarily the safest option. An indirect way to secure staff accounts, and ultimately root access is to use an alternative login access method and do what is known as starring out the encrypted password for the staff accounts. Using the &man.vipw.8; command, one can replace each instance of an encrypted password with a single * character. This command will update the /etc/master.passwd file and user/password database to disable password-authenticated logins. A staff account entry such as: foobar:R9DT/Fa1/LV9U:1000:1000::0:0:Foo Bar:/home/foobar:/usr/local/bin/tcsh Should be changed to this: foobar:*:1000:1000::0:0:Foo Bar:/home/foobar:/usr/local/bin/tcsh This change will prevent normal logins from occurring, since the encrypted password will never match *. With this done, staff members must use another mechanism to authenticate themselves such as &man.kerberos.1; or &man.ssh.1; using a public/private key pair. When using something like Kerberos, one generally must secure the machines which run the Kerberos servers and your desktop workstation. When using a public/private key pair with ssh, one must generally secure the machine used to login from (typically one's workstation). An additional layer of protection can be added to the key pair by password protecting the key pair when creating it with &man.ssh-keygen.1;. Being able to star out the passwords for staff accounts also guarantees that staff members can only login through secure access methods that you have setup. This forces all staff members to use secure, encrypted connections for all of their sessions, which closes an important hole used by many intruders: sniffing the network from an unrelated, less secure machine. The more indirect security mechanisms also assume that you are logging in from a more restrictive server to a less restrictive server. For example, if your main box is running all sorts of servers, your workstation should not be running any. In order for your workstation to be reasonably secure you should run as few servers as possible, up to and including no servers at all, and you should run a password-protected screen blanker. Of course, given physical access to a workstation an attacker can break any sort of security you put on it. This is definitely a problem that you should consider, but you should also consider the fact that the vast majority of break-ins occur remotely, over a network, from people who do not have physical access to your workstation or servers. Kerberos Using something like Kerberos also gives you the ability to disable or change the password for a staff account in one place, and have it immediately effect all the machines on which the staff member may have an account. If a staff member's account gets compromised, the ability to instantly change his password on all machines should not be underrated. With discrete passwords, changing a password on N machines can be a mess. You can also impose re-passwording restrictions with Kerberos: not only can a Kerberos ticket be made to timeout after a while, but the Kerberos system can require that the user choose a new password after a certain period of time (say, once a month). Securing Root-run Servers and SUID/SGID Binaries ntalk comsat finger sandboxes sshd telnetd rshd rlogind The prudent sysadmin only runs the servers he needs to, no more, no less. Be aware that third party servers are often the most bug-prone. For example, running an old version of imapd or popper is like giving a universal root ticket out to the entire world. Never run a server that you have not checked out carefully. Many servers do not need to be run as root. For example, the ntalk, comsat, and finger daemons can be run in special user sandboxes. A sandbox is not perfect, unless you go through a large amount of trouble, but the onion approach to security still stands: If someone is able to break in through a server running in a sandbox, they still have to break out of the sandbox. The more layers the attacker must break through, the lower the likelihood of his success. Root holes have historically been found in virtually every server ever run as root, including basic system servers. If you are running a machine through which people only login via sshd and never login via telnetd or rshd or rlogind, then turn off those services! FreeBSD now defaults to running ntalkd, comsat, and finger in a sandbox. Another program which may be a candidate for running in a sandbox is &man.named.8;. /etc/defaults/rc.conf includes the arguments necessary to run named in a sandbox in a commented-out form. Depending on whether you are installing a new system or upgrading an existing system, the special user accounts used by these sandboxes may not be installed. The prudent sysadmin would research and implement sandboxes for servers whenever possible. sendmail There are a number of other servers that typically do not run in sandboxes: sendmail, popper, imapd, ftpd, and others. There are alternatives to some of these, but installing them may require more work than you are willing to perform (the convenience factor strikes again). You may have to run these servers as root and rely on other mechanisms to detect break-ins that might occur through them. The other big potential root holes in a system are the suid-root and sgid binaries installed on the system. Most of these binaries, such as rlogin, reside in /bin, /sbin, /usr/bin, or /usr/sbin. While nothing is 100% safe, the system-default suid and sgid binaries can be considered reasonably safe. Still, root holes are occasionally found in these binaries. A root hole was found in Xlib in 1998 that made xterm (which is typically suid) vulnerable. It is better to be safe than sorry and the prudent sysadmin will restrict suid binaries, that only staff should run, to a special group that only staff can access, and get rid of (chmod 000) any suid binaries that nobody uses. A server with no display generally does not need an xterm binary. Sgid binaries can be almost as dangerous. If an intruder can break an sgid-kmem binary, the intruder might be able to read /dev/kmem and thus read the encrypted password file, potentially compromising any passworded account. Alternatively an intruder who breaks group kmem can monitor keystrokes sent through pty's, including pty's used by users who login through secure methods. An intruder that breaks the tty group can write to almost any user's tty. If a user is running a terminal program or emulator with a keyboard-simulation feature, the intruder can potentially generate a data stream that causes the user's terminal to echo a command, which is then run as that user. Securing User Accounts User accounts are usually the most difficult to secure. While you can impose Draconian access restrictions on your staff and star out their passwords, you may not be able to do so with any general user accounts you might have. If you do have sufficient control, then you may win out and be able to secure the user accounts properly. If not, you simply have to be more vigilant in your monitoring of those accounts. Use of ssh and Kerberos for user accounts is more problematic, due to the extra administration and technical support required, but still a very good solution compared to a crypted password file. Securing the Password File The only sure fire way is to * out as many passwords as you can and use ssh or Kerberos for access to those accounts. Even though the encrypted password file (/etc/spwd.db) can only be read by root, it may be possible for an intruder to obtain read access to that file even if the attacker cannot obtain root-write access. Your security scripts should always check for and report changes to the password file (see the Checking file integrity section below). Securing the Kernel Core, Raw Devices, and Filesystems If an attacker breaks root he can do just about anything, but there are certain conveniences. For example, most modern kernels have a packet sniffing device driver built in. Under FreeBSD it is called the bpf device. An intruder will commonly attempt to run a packet sniffer on a compromised machine. You do not need to give the intruder the capability and most systems do not have the need for the bpf device compiled in. sysctl But even if you turn off the bpf device, you still have /dev/mem and /dev/kmem to worry about. For that matter, the intruder can still write to raw disk devices. Also, there is another kernel feature called the module loader, &man.kldload.8;. An enterprising intruder can use a KLD module to install his own bpf device, or other sniffing device, on a running kernel. To avoid these problems you have to run the kernel at a higher secure level, at least securelevel 1. The securelevel can be set with a sysctl on the kern.securelevel variable. Once you have set the securelevel to 1, write access to raw devices will be denied and special chflags flags, such as schg, will be enforced. You must also ensure that the schg flag is set on critical startup binaries, directories, and script files – everything that gets run up to the point where the securelevel is set. This might be overdoing it, and upgrading the system is much more difficult when you operate at a higher secure level. You may compromise and run the system at a higher secure level but not set the schg flag for every system file and directory under the sun. Another possibility is to simply mount / and /usr read-only. It should be noted that being too Draconian in what you attempt to protect may prevent the all-important detection of an intrusion. Checking File Integrity: Binaries, Configuration Files, Etc. When it comes right down to it, you can only protect your core system configuration and control files so much before the convenience factor rears its ugly head. For example, using chflags to set the schg bit on most of the files in / and /usr is probably counterproductive, because while it may protect the files, it also closes a detection window. The last layer of your security onion is perhaps the most important – detection. The rest of your security is pretty much useless (or, worse, presents you with a false sense of safety) if you cannot detect potential incursions. Half the job of the onion is to slow down the attacker, rather than stop him, in order to give the detection side of the equation a chance to catch him in the act. The best way to detect an incursion is to look for modified, missing, or unexpected files. The best way to look for modified files is from another (often centralized) limited-access system. Writing your security scripts on the extra-secure limited-access system makes them mostly invisible to potential attackers, and this is important. In order to take maximum advantage you generally have to give the limited-access box significant access to the other machines in the business, usually either by doing a read-only NFS export of the other machines to the limited-access box, or by setting up ssh key-pairs to allow the limited-access box to ssh to the other machines. Except for its network traffic, NFS is the least visible method – allowing you to monitor the filesystems on each client box virtually undetected. If your limited-access server is connected to the client boxes through a switch, the NFS method is often the better choice. If your limited-access server is connected to the client boxes through a hub, or through several layers of routing, the NFS method may be too insecure (network-wise) and using ssh may be the better choice even with the audit-trail tracks that ssh lays. Once you give a limited-access box, at least read access to the client systems it is supposed to monitor, you must write scripts to do the actual monitoring. Given an NFS mount, you can write scripts out of simple system utilities such as &man.find.1; and &man.md5.1;. It is best to physically md5 the client-box files at least once a day, and to test control files such as those found in /etc and /usr/local/etc even more often. When mismatches are found, relative to the base md5 information the limited-access machine knows is valid, it should scream at a sysadmin to go check it out. A good security script will also check for inappropriate suid binaries and for new or deleted files on system partitions such as / and /usr. When using ssh rather than NFS, writing the security script is much more difficult. You essentially have to scp the scripts to the client box in order to run them, making them visible, and for safety you also need to scp the binaries (such as find) that those scripts use. The ssh client on the client box may already be compromised. All in all, using ssh may be necessary when running over insecure links, but it is also a lot harder to deal with. A good security script will also check for changes to user and staff members access configuration files: .rhosts, .shosts, .ssh/authorized_keys and so forth… files that might fall outside the purview of the MD5 check. If you have a huge amount of user disk space, it may take too long to run through every file on those partitions. In this case, setting mount flags to disallow suid binaries and devices on those partitions is a good idea. The nodev and nosuid options (see &man.mount.8;) are what you want to look into. You should probably scan them anyway, at least once a week, since the object of this layer is to detect a break-in whether or not the break-in is effective. Process accounting (see &man.accton.8;) is a relatively low-overhead feature of the operating system which might help as a post-break-in evaluation mechanism. It is especially useful in tracking down how an intruder has actually broken into a system, assuming the file is still intact after the break-in occurs. Finally, security scripts should process the log files, and the logs themselves should be generated in as secure a manner as possible – remote syslog can be very useful. An intruder tries to cover his tracks, and log files are critical to the sysadmin trying to track down the time and method of the initial break-in. One way to keep a permanent record of the log files is to run the system console to a serial port and collect the information on a continuing basis through a secure machine monitoring the consoles. Paranoia A little paranoia never hurts. As a rule, a sysadmin can add any number of security features, as long as they do not effect convenience, and can add security features that do effect convenience with some added thought. Even more importantly, a security administrator should mix it up a bit – if you use recommendations such as those given by this document verbatim, you give away your methodologies to the prospective attacker who also has access to this document. Denial of Service Attacks Denial of Service (DoS) This section covers Denial of Service attacks. A DoS attack is typically a packet attack. While there is not much you can do about modern spoofed packet attacks that saturate your network, you can generally limit the damage by ensuring that the attacks cannot take down your servers. Limiting server forks. Limiting springboard attacks (ICMP response attacks, ping broadcast, etc.). Kernel Route Cache. A common DoS attack is against a forking server that attempts to cause the server to eat processes, file descriptors, and memory, until the machine dies. inetd (see &man.inetd.8;) has several options to limit this sort of attack. It should be noted that while it is possible to prevent a machine from going down, it is not generally possible to prevent a service from being disrupted by the attack. Read the inetd manual page carefully and pay specific attention to the , , and options. Note that spoofed-IP attacks will circumvent the option to inetd, so typically a combination of options must be used. Some standalone servers have self-fork-limitation parameters. Sendmail has its option, which tends to work much better than trying to use sendmail's load limiting options due to the load lag. You should specify a MaxDaemonChildren parameter, when you start sendmail, high enough to handle your expected load, but not so high that the computer cannot handle that number of sendmails without falling on its face. It is also prudent to run sendmail in queued mode () and to run the daemon (sendmail -bd) separate from the queue-runs (sendmail -q15m). If you still want real-time delivery you can run the queue at a much lower interval, such as , but be sure to specify a reasonable MaxDaemonChildren option for that sendmail to prevent cascade failures. Syslogd can be attacked directly and it is strongly recommended that you use the option whenever possible, and the option otherwise. You should also be fairly careful with connect-back services such as tcpwrapper's reverse-identd, which can be attacked directly. You generally do not want to use the reverse-ident feature of tcpwrappers for this reason. It is a very good idea to protect internal services from external access by firewalling them off at your border routers. The idea here is to prevent saturation attacks from outside your LAN, not so much to protect internal services from network-based root compromise. Always configure an exclusive firewall, i.e., firewall everything except ports A, B, C, D, and M-Z. This way you can firewall off all of your low ports except for certain specific services such as named (if you are primary for a zone), ntalkd, sendmail, and other Internet-accessible services. If you try to configure the firewall the other way – as an inclusive or permissive firewall, there is a good chance that you will forget to close a couple of services, or that you will add a new internal service and forget to update the firewall. You can still open up the high-numbered port range on the firewall, to allow permissive-like operation, without compromising your low ports. Also take note that FreeBSD allows you to control the range of port numbers used for dynamic binding, via the various net.inet.ip.portrange sysctl's (sysctl -a | fgrep portrange), which can also ease the complexity of your firewall's configuration. For example, you might use a normal first/last range of 4000 to 5000, and a hiport range of 49152 to 65535, then block off everything under 4000 in your firewall (except for certain specific Internet-accessible ports, of course). ICMP_BANDLIM Another common DoS attack is called a springboard attack – to attack a server in a manner that causes the server to generate responses which overloads the server, the local network, or some other machine. The most common attack of this nature is the ICMP ping broadcast attack. The attacker spoofs ping packets sent to your LAN's broadcast address with the source IP address set to the actual machine they wish to attack. If your border routers are not configured to stomp on ping's to broadcast addresses, your LAN winds up generating sufficient responses to the spoofed source address to saturate the victim, especially when the attacker uses the same trick on several dozen broadcast addresses over several dozen different networks at once. Broadcast attacks of over a hundred and twenty megabits have been measured. A second common springboard attack is against the ICMP error reporting system. By constructing packets that generate ICMP error responses, an attacker can saturate a server's incoming network and cause the server to saturate its outgoing network with ICMP responses. This type of attack can also crash the server by running it out of mbuf's, especially if the server cannot drain the ICMP responses it generates fast enough. The FreeBSD kernel has a new kernel compile option called which limits the effectiveness of these sorts of attacks. The last major class of springboard attacks is related to certain internal inetd services such as the udp echo service. An attacker simply spoofs a UDP packet with the source address being server A's echo port, and the destination address being server B's echo port, where server A and B are both on your LAN. The two servers then bounce this one packet back and forth between each other. The attacker can overload both servers and their LANs simply by injecting a few packets in this manner. Similar problems exist with the internal chargen port. A competent sysadmin will turn off all of these inetd-internal test services. Spoofed packet attacks may also be used to overload the kernel route cache. Refer to the net.inet.ip.rtexpire, rtminexpire, and rtmaxcache sysctl parameters. A spoofed packet attack that uses a random source IP will cause the kernel to generate a temporary cached route in the route table, viewable with netstat -rna | fgrep W3. These routes typically timeout in 1600 seconds or so. If the kernel detects that the cached route table has gotten too big it will dynamically reduce the rtexpire but will never decrease it to less than rtminexpire. There are two problems: The kernel does not react quickly enough when a lightly loaded server is suddenly attacked. The rtminexpire is not low enough for the kernel to survive a sustained attack. If your servers are connected to the Internet via a T3 or better, it may be prudent to manually override both rtexpire and rtminexpire via &man.sysctl.8;. Never set either parameter to zero (unless you want to crash the machine). Setting both parameters to 2 seconds should be sufficient to protect the route table from attack. Access Issues with Kerberos and SSH ssh Kerberos There are a few issues with both Kerberos and ssh that need to be addressed if you intend to use them. Kerberos V is an excellent authentication protocol, but there are bugs in the kerberized telnet and rlogin applications that make them unsuitable for dealing with binary streams. Also, by default Kerberos does not encrypt a session unless you use the option. ssh encrypts everything by default. ssh works quite well in every respect except that it forwards encryption keys by default. What this means is that if you have a secure workstation holding keys that give you access to the rest of the system, and you ssh to an insecure machine, your keys are usable. The actual keys themselves are not exposed, but ssh installs a forwarding port for the duration of your login, and if an attacker has broken root on the insecure machine he can utilize that port to use your keys to gain access to any other machine that your keys unlock. We recommend that you use ssh in combination with Kerberos whenever possible for staff logins. ssh can be compiled with Kerberos support. This reduces your reliance on potentially exposable ssh keys while at the same time protecting passwords via Kerberos. ssh keys should only be used for automated tasks from secure machines (something that Kerberos is unsuited to do). We also recommend that you either turn off key-forwarding in the ssh configuration, or that you make use of the from=IP/DOMAIN option that ssh allows in its authorized_keys file to make the key only usable to entities logging in from specific machines. Bill Swingle Parts rewritten and updated by DES, MD5, and Crypt security crypt crypt DES MD5 Every user on a Unix system has a password associated with their account. It seems obvious that these passwords need to be known only to the user and the actual operating system. In order to keep these passwords secret, they are encrypted with what is known as a one-way hash, that is, they can only be easily encrypted but not decrypted. In other words, what we told you a moment ago was obvious is not even true: the operating system itself does not really know the password. It only knows the encrypted form of the password. The only way to get the plain-text password is by a brute force search of the space of possible passwords. Unfortunately the only secure way to encrypt passwords when Unix came into being was based on DES, the Data Encryption Standard. This was not such a problem for users resident in the US, but since the source code for DES could not be exported outside the US, FreeBSD had to find a way to both comply with US law and retain compatibility with all the other Unix variants that still used DES. The solution was to divide up the encryption libraries so that US users could install the DES libraries and use DES but international users still had an encryption method that could be exported abroad. This is how FreeBSD came to use MD5 as its default encryption method. MD5 is believed to be more secure than DES, so installing DES is offered primarily for compatibility reasons. Recognizing Your Crypt Mechanism - Before FreeBSD 4.4 libcrypt.a was a + Before FreeBSD 4.4 libcrypt.a was a symbolic link pointing to the library which was used for - encryption. FreeBSD 4.4 changed libcrypt.a to + encryption. FreeBSD 4.4 changed libcrypt.a to provide a configurable password authentication hash library. Currently the library supports DES, MD5 and Blowfish hash functions. By default FreeBSD uses MD5 to encrypt passwords. It is pretty easy to identify which encryption method FreeBSD is set up to use. Examining the encrypted passwords in the /etc/master.passwd file is one way. Passwords encrypted with the MD5 hash are longer than those encrypted with the DES hash and also begin with the characters $1$. Passwords starting with $2$ are encrypted with the Blowfish hash function. DES password strings do not have any particular identifying characteristics, but they are shorter than MD5 passwords, and are coded in a 64-character alphabet which does not include the $ character, so a relatively short string which does not begin with a dollar sign is very likely a DES password. The password format used for new passwords is controlled by the passwd_format login capability in /etc/login.conf, which takes values of des or md5 or blf. See the &man.login.conf.5; manual page for more information about login capabilities. S/Key S/Key security S/Key S/Key is a one-time password scheme based on a one-way hash function. FreeBSD uses the MD4 hash for compatibility but other systems have used MD5 and DES-MAC. S/Key has been part of the FreeBSD base system since version 1.1.5 and is also used on a growing number of other operating systems. S/Key is a registered trademark of Bell Communications Research, Inc. From version 5.0 of FreeBSD, S/Key has been replaced with the functionally equivalent OPIE (Onetime Passwords In Everything). OPIE uses the MD5 hash by default. There are three different sorts of passwords which we will talk about in the discussion below. The first is your usual Unix-style or Kerberos password; we will call this a Unix password. The second sort is the one-time password which is generated by the S/Key key program or the OPIE opiekey program and accepted by the keyinit or opiepasswd programs and the login prompt; we will call this a one-time password. The final sort of password is the secret password which you give to the key/opiekey programs (and sometimes the keyinit/opiepasswd programs) which it uses to generate one-time passwords; we will call it a secret password or just unqualified password. The secret password does not have anything to do with your Unix password; they can be the same but this is not recommended. S/Key and OPIE secret passwords are not limited to 8 characters like Unix passwords, they can be as long as you like. Passwords of six or seven word long phrases are fairly common. For the most part, the S/Key or OPIE system operates completely independently of the Unix password system. Besides the password, there are two other pieces of data that are important to S/Key and OPIE. One is what is known as the seed or key, consisting of two letters and five digits. The other is what is called the iteration count, a number between 1 and 100. S/Key creates the one-time password by concatenating the seed and the secret password, then applying the MD4/MD5 hash as many times as specified by the iteration count and turning the result into six short English words. These six English words are your one-time password. The authentication system (primarily PAM) keeps track of the last one-time password used, and the user is authenticated if the hash of the user-provided password is equal to the previous password. Because a one-way hash is used it is impossible to generate future one-time passwords if a successfully used password is captured; the iteration count is decremented after each successful login to keep the user and the login program in sync. When the iteration count gets down to 1, S/Key and OPIE must be reinitialized. There are three programs involved in each system which we will discuss below. The key and opiekey programs accept an iteration count, a seed, and a secret password, and generate a one-time password or a consecutive list of one-time passwords. The keyinit and opiepasswd programs are used to initialize S/Key and OPIE respectively, and to change passwords, iteration counts, or seeds; they take either a secret passphrase, or an iteration count, seed, and one-time password. The keyinfo and opieinfo programs examine the relevant credentials files (/etc/skeykeys or /etc/opiekeys) and print out the invoking user's current iteration count and seed. There are four different sorts of operations we will cover. The first is using keyinit or opiepasswd over a secure connection to set up one-time-passwords for the first time, or to change your password or seed. The second operation is using keyinit or opiepasswd over an insecure connection, in conjunction with key or opiekey over a secure connection, to do the same. The third is using key/opiekey to log in over an insecure connection. The fourth is using key or opiekey to generate a number of keys which can be written down or printed out to carry with you when going to some location without secure connections to anywhere. Secure Connection Initialization To initialize S/Key for the first time, change your password, or change your seed while logged in over a secure connection (e.g., on the console of a machine or via ssh), use the keyinit command without any parameters while logged in as yourself: &prompt.user; keyinit Adding unfurl: Reminder - Only use this method if you are directly connected. If you are using telnet or rlogin exit with no password and use keyinit -s. Enter secret password: Again secret password: ID unfurl s/key is 99 to17757 DEFY CLUB PRO NASH LACE SOFT For OPIE, opiepasswd is used instead: &prompt.user; opiepasswd -c [grimreaper] ~ $ opiepasswd -f -c Adding unfurl: Only use this method from the console; NEVER from remote. If you are using telnet, xterm, or a dial-in, type ^C now or exit with no password. Then run opiepasswd without the -c parameter. Using MD5 to compute responses. Enter new secret pass phrase: Again new secret pass phrase: ID unfurl OTP key is 499 to4268 MOS MALL GOAT ARM AVID COED At the Enter new secret pass phrase: or Enter secret password: prompts, you should enter a password or phrase. Remember, this is not the password that you will use to login with, this is used to generate your one-time login keys. The ID line gives the parameters of your particular instance; your login name, the iteration count, and seed. When logging in the system will remember these parameters and present them back to you so you do not have to remember them. The last line gives the particular one-time password which corresponds to those parameters and your secret password; if you were to re-login immediately, this one-time password is the one you would use. Insecure Connection Initialization To initialize or change your secret password over an insecure connection, you will need to already have a secure connection to some place where you can run key or opiekey; this might be in the form of a desk accessory on a Macintosh, or a shell prompt on a machine you trust. You will also need to make up an iteration count (100 is probably a good value), and you may make up your own seed or use a randomly-generated one. Over on the insecure connection (to the machine you are initializing), use the keyinit -s command: &prompt.user; keyinit -s Updating unfurl: Old key: to17758 Reminder you need the 6 English words from the key command. Enter sequence count from 1 to 9999: 100 Enter new key [default to17759]: s/key 100 to 17759 s/key access password: s/key access password:CURE MIKE BANE HIM RACY GORE For OPIE, you need to use opiepasswd: &prompt.user; opiepasswd Updating unfurl: You need the response from an OTP generator. Old secret pass phrase: otp-md5 498 to4268 ext Response: GAME GAG WELT OUT DOWN CHAT New secret pass phrase: otp-md5 499 to4269 Response: LINE PAP MILK NELL BUOY TROY ID mark OTP key is 499 gr4269 LINE PAP MILK NELL BUOY TROY To accept the default seed (which the keyinit program confusingly calls a key), press Return. Then before entering an access password, move over to your secure connection or S/Key desk accessory, and give it the same parameters: &prompt.user; key 100 to17759 Reminder - Do not use this program while logged in via telnet or rlogin. Enter secret password: <secret password> CURE MIKE BANE HIM RACY GORE Or for OPIE: &prompt.user; opiekey 498 to4268 Using the MD5 algorithm to compute response. Reminder: Don't use opiekey from telnet or dial-in sessions. Enter secret pass phrase: GAME GAG WELT OUT DOWN CHAT Now switch back over to the insecure connection, and copy the one-time password generated over to the relevant program. Generating a Single one-time Password Once you have initialized S/Key or OPIE, when you login you will be presented with a prompt like this: &prompt.user; telnet example.com Trying 10.0.0.1... Connected to example.com Escape character is '^]'. FreeBSD/i386 (example.com) (ttypa) login: <username> s/key 97 fw13894 Password: Or for OPIE: &prompt.user; telnet example.com Trying 10.0.0.1... Connected to example.com Escape character is '^]'. FreeBSD/i386 (example.com) (ttypa) login: <username> otp-md5 498 gr4269 ext Password: As a side note, the S/Key and OPIE prompts have a useful feature (not shown here): if you press Return at the password prompt, the prompter will turn echo on, so you can see what you are typing. This can be extremely useful if you are attempting to type in a password by hand, such as from a printout. MS-DOS Windows MacOS At this point you need to generate your one-time password to answer this login prompt. This must be done on a trusted system that you can run key or opiekey on. (There are versions of these for DOS, Windows and MacOS as well.) They need both the iteration count and the seed as command line options. You can cut-and-paste these right from the login prompt on the machine that you are logging in to. On the trusted system: &prompt.user; key 97 fw13894 Reminder - Do not use this program while logged in via telnet or rlogin. Enter secret password: WELD LIP ACTS ENDS ME HAAG For OPIE: &prompt.user; opiekey 498 to4268 Using the MD5 algorithm to compute response. Reminder: Don't use opiekey from telnet or dial-in sessions. Enter secret pass phrase: GAME GAG WELT OUT DOWN CHAT Now that you have your one-time password you can continue logging in: login: <username> s/key 97 fw13894 Password: <return to enable echo> s/key 97 fw13894 Password [echo on]: WELD LIP ACTS ENDS ME HAAG Last login: Tue Mar 21 11:56:41 from 10.0.0.2 ... Generating Multiple one-time Passwords Sometimes you have to go places where you do not have access to a trusted machine or secure connection. In this case, it is possible to use the key command to generate a number of one-time passwords before hand to be printed out and taken with you. For example: &prompt.user; key -n 5 30 zz99999 Reminder - Do not use this program while logged in via telnet or rlogin. Enter secret password: <secret password> 26: SODA RUDE LEA LIND BUDD SILT 27: JILT SPY DUTY GLOW COWL ROT 28: THEM OW COLA RUNT BONG SCOT 29: COT MASH BARR BRIM NAN FLAG 30: CAN KNEE CAST NAME FOLK BILK The requests five keys in sequence, the specifies what the last iteration number should be. Note that these are printed out in reverse order of eventual use. If you are really paranoid, you might want to write the results down by hand; otherwise you can cut-and-paste into lpr. Note that each line shows both the iteration count and the one-time password; you may still find it handy to scratch off passwords as you use them. Restricting Use of Unix Passwords Restrictions can be placed on the use of Unix passwords based on the host name, user name, terminal port, or IP address of a login session. These restrictions can be found in the configuration file /etc/skey.access. The &man.skey.access.5; manual page has more information on the complete format of the file and also details some security cautions to be aware of before depending on this file for security. If there is no /etc/skey.access file (this is the FreeBSD default), then all users will be allowed to use Unix passwords. If the file exists, however, then all users will be required to use S/Key unless explicitly permitted to do otherwise by configuration statements in the skey.access file. In all cases, Unix passwords are permitted on the console. Here is a sample configuration file which illustrates the three most common sorts of configuration statements: permit internet 192.168.0.0 255.255.0.0 permit user fnord permit port ttyd0 The first line (permit internet) allows users whose IP source address (which is vulnerable to spoofing) matches the specified value and mask, to use Unix passwords. This should not be considered a security mechanism, but rather, a means to remind authorized users that they are using an insecure network and need to use S/Key for authentication. The second line (permit user) allows the specified username, in this case fnord, to use Unix passwords at any time. Generally speaking, this should only be used for people who are either unable to use the key program, like those with dumb terminals, or those who are uneducable. The third line (permit port) allows all users logging in on the specified terminal line to use Unix passwords; this would be used for dial-ups. Mark Murray Contributed by Mark Dapoz Based on a contribution by Kerberos Kerberos Kerberos is a network add-on system/protocol that allows users to authenticate themselves through the services of a secure server. Services such as remote login, remote copy, secure inter-system file copying and other high-risk tasks are made considerably safer and more controllable. The following instructions can be used as a guide on how to set up Kerberos as distributed for FreeBSD. However, you should refer to the relevant manual pages for a complete description. Installing Kerberos MIT Kerberos installing Kerberos is an optional component of FreeBSD. The easiest way to install this software is by selecting the 'krb4' or 'krb5' distribution in sysinstall during the initial installation of FreeBSD. This will install the 'eBones' (KerberosIV) or 'Heimdal' (Kerberos5) implementation of Kerberos. These implementations are included because they are developed outside the USA/Canada and were thus available to system owners outside those countries during the era of restrictive export controls on cryptographic code from the USA. Alternatively, the MIT implementation of Kerberos is available from the ports collection as security/krb5. Creating the Initial Database This is done on the Kerberos server only. First make sure that you do not have any old Kerberos databases around. You should change to the directory /etc/kerberosIV and check that only the following files are present: &prompt.root; cd /etc/kerberosIV &prompt.root; ls README krb.conf krb.realms If any additional files (such as principal.* or master_key) exist, then use the kdb_destroy command to destroy the old Kerberos database, or if Kerberos is not running, simply delete the extra files. You should now edit the krb.conf and krb.realms files to define your Kerberos realm. In this case the realm will be EXAMPLE.COM and the server is grunt.example.com. We edit or create the krb.conf file: &prompt.root; cat krb.conf EXAMPLE.COM EXAMPLE.COM grunt.example.com admin server CS.BERKELEY.EDU okeeffe.berkeley.edu ATHENA.MIT.EDU kerberos.mit.edu ATHENA.MIT.EDU kerberos-1.mit.edu ATHENA.MIT.EDU kerberos-2.mit.edu ATHENA.MIT.EDU kerberos-3.mit.edu LCS.MIT.EDU kerberos.lcs.mit.edu TELECOM.MIT.EDU bitsy.mit.edu ARC.NASA.GOV trident.arc.nasa.gov In this case, the other realms do not need to be there. They are here as an example of how a machine may be made aware of multiple realms. You may wish to not include them for simplicity. The first line names the realm in which this system works. The other lines contain realm/host entries. The first item on a line is a realm, and the second is a host in that realm that is acting as a key distribution center. The words admin server following a host's name means that host also provides an administrative database server. For further explanation of these terms, please consult the Kerberos manual pages. Now we have to add grunt.example.com to the EXAMPLE.COM realm and also add an entry to put all hosts in the .example.com domain in the EXAMPLE.COM realm. The krb.realms file would be updated as follows: &prompt.root; cat krb.realms grunt.example.com EXAMPLE.COM .example.com EXAMPLE.COM .berkeley.edu CS.BERKELEY.EDU .MIT.EDU ATHENA.MIT.EDU .mit.edu ATHENA.MIT.EDU Again, the other realms do not need to be there. They are here as an example of how a machine may be made aware of multiple realms. You may wish to remove them to simplify things. The first line puts the specific system into the named realm. The rest of the lines show how to default systems of a particular subdomain to a named realm. Now we are ready to create the database. This only needs to run on the Kerberos server (or Key Distribution Center). Issue the kdb_init command to do this: &prompt.root; kdb_init Realm name [default ATHENA.MIT.EDU ]: EXAMPLE.COM You will be prompted for the database Master Password. It is important that you NOT FORGET this password. Enter Kerberos master key: Now we have to save the key so that servers on the local machine can pick it up. Use the kstash command to do this. &prompt.root; kstash Enter Kerberos master key: Current Kerberos master key version is 1. Master key entered. BEWARE! This saves the encrypted master password in /etc/kerberosIV/master_key. Making It All Run Two principals need to be added to the database for each system that will be secured with Kerberos. Their names are kpasswd and rcmd These two principals are made for each system, with the instance being the name of the individual system. These daemons, kpasswd and rcmd allow other systems to change Kerberos passwords and run commands like rcp, rlogin and rsh. Now let us add these entries: &prompt.root; kdb_edit Opening database... Enter Kerberos master key: Current Kerberos master key version is 1. Master key entered. BEWARE! Previous or default values are in [brackets] , enter return to leave the same, or new value. Principal name: passwd Instance: grunt <Not found>, Create [y] ? y Principal: passwd, Instance: grunt, kdc_key_ver: 1 New Password: <---- enter RANDOM here Verifying password New Password: <---- enter RANDOM here Random password [y] ? y Principal's new key version = 1 Expiration date (enter yyyy-mm-dd) [ 2000-01-01 ] ? Max ticket lifetime (*5 minutes) [ 255 ] ? Attributes [ 0 ] ? Edit O.K. Principal name: rcmd Instance: grunt <Not found>, Create [y] ? Principal: rcmd, Instance: grunt, kdc_key_ver: 1 New Password: <---- enter RANDOM here Verifying password New Password: <---- enter RANDOM here Random password [y] ? Principal's new key version = 1 Expiration date (enter yyyy-mm-dd) [ 2000-01-01 ] ? Max ticket lifetime (*5 minutes) [ 255 ] ? Attributes [ 0 ] ? Edit O.K. Principal name: <---- null entry here will cause an exit Creating the Server File We now have to extract all the instances which define the services on each machine. For this we use the ext_srvtab command. This will create a file which must be copied or moved by secure means to each Kerberos client's /etc/kerberosIV directory. This file must be present on each server and client, and is crucial to the operation of Kerberos. &prompt.root; ext_srvtab grunt Enter Kerberos master key: Current Kerberos master key version is 1. Master key entered. BEWARE! Generating 'grunt-new-srvtab'.... Now, this command only generates a temporary file which must be renamed to srvtab so that all the servers can pick it up. Use the mv command to move it into place on the original system: &prompt.root; mv grunt-new-srvtab srvtab If the file is for a client system, and the network is not deemed safe, then copy the client-new-srvtab to removable media and transport it by secure physical means. Be sure to rename it to srvtab in the client's /etc/kerberosIV directory, and make sure it is mode 600: &prompt.root; mv grumble-new-srvtab srvtab &prompt.root; chmod 600 srvtab Populating the Database We now have to add some user entries into the database. First let us create an entry for the user jane. Use the kdb_edit command to do this: &prompt.root; kdb_edit Opening database... Enter Kerberos master key: Current Kerberos master key version is 1. Master key entered. BEWARE! Previous or default values are in [brackets] , enter return to leave the same, or new value. Principal name: jane Instance: <Not found>, Create [y] ? y Principal: jane, Instance: , kdc_key_ver: 1 New Password: <---- enter a secure password here Verifying password New Password: <---- re-enter the password here Principal's new key version = 1 Expiration date (enter yyyy-mm-dd) [ 2000-01-01 ] ? Max ticket lifetime (*5 minutes) [ 255 ] ? Attributes [ 0 ] ? Edit O.K. Principal name: <---- null entry here will cause an exit Testing It All Out First we have to start the Kerberos daemons. NOTE that if you have correctly edited your /etc/rc.conf then this will happen automatically when you reboot. This is only necessary on the Kerberos server. Kerberos clients will automagically get what they need from the /etc/kerberosIV directory. &prompt.root; kerberos & Kerberos server starting Sleep forever on error Log file is /var/log/kerberos.log Current Kerberos master key version is 1. Master key entered. BEWARE! Current Kerberos master key version is 1 Local realm: EXAMPLE.COM &prompt.root; kadmind -n & KADM Server KADM0.0A initializing Please do not use 'kill -9' to kill this job, use a regular kill instead Current Kerberos master key version is 1. Master key entered. BEWARE! Now we can try using the kinit command to get a ticket for the id jane that we created above: &prompt.user; kinit jane MIT Project Athena (grunt.example.com) Kerberos Initialization for "jane" Password: Try listing the tokens using klist to see if we really have them: &prompt.user; klist Ticket file: /tmp/tkt245 Principal: jane@EXAMPLE.COM Issued Expires Principal Apr 30 11:23:22 Apr 30 19:23:22 krbtgt.EXAMPLE.COM@EXAMPLE.COM Now try changing the password using passwd to check if the kpasswd daemon can get authorization to the Kerberos database: &prompt.user; passwd realm EXAMPLE.COM Old password for jane: New Password for jane: Verifying password New Password for jane: Password changed. Adding <command>su</command> Privileges Kerberos allows us to give each user who needs root privileges their own separate su password. We could now add an id which is authorized to su to root. This is controlled by having an instance of root associated with a principal. Using kdb_edit we can create the entry jane.root in the Kerberos database: &prompt.root; kdb_edit Opening database... Enter Kerberos master key: Current Kerberos master key version is 1. Master key entered. BEWARE! Previous or default values are in [brackets] , enter return to leave the same, or new value. Principal name: jane Instance: root <Not found>, Create [y] ? y Principal: jane, Instance: root, kdc_key_ver: 1 New Password: <---- enter a SECURE password here Verifying password New Password: <---- re-enter the password here Principal's new key version = 1 Expiration date (enter yyyy-mm-dd) [ 2000-01-01 ] ? Max ticket lifetime (*5 minutes) [ 255 ] ? 12 <--- Keep this short! Attributes [ 0 ] ? Edit O.K. Principal name: <---- null entry here will cause an exit Now try getting tokens for it to make sure it works: &prompt.root; kinit jane.root MIT Project Athena (grunt.example.com) Kerberos Initialization for "jane.root" Password: Now we need to add the user to root's .klogin file: &prompt.root; cat /root/.klogin jane.root@EXAMPLE.COM Now try doing the su: &prompt.user; su Password: and take a look at what tokens we have: &prompt.root; klist Ticket file: /tmp/tkt_root_245 Principal: jane.root@EXAMPLE.COM Issued Expires Principal May 2 20:43:12 May 3 04:43:12 krbtgt.EXAMPLE.COM@EXAMPLE.COM Using Other Commands In an earlier example, we created a principal called jane with an instance root. This was based on a user with the same name as the principal, and this is a Kerberos default; that a <principal>.<instance> of the form <username>.root will allow that <username> to su to root if the necessary entries are in the .klogin file in root's home directory: &prompt.root; cat /root/.klogin jane.root@EXAMPLE.COM Likewise, if a user has in their own home directory lines of the form: &prompt.user; cat ~/.klogin jane@EXAMPLE.COM jack@EXAMPLE.COM This allows anyone in the EXAMPLE.COM realm who has authenticated themselves to jane or jack (via kinit, see above) access to rlogin to jane's account or files on this system (grunt) via rlogin, rsh or rcp. For example, jane now logs into another system using Kerberos: &prompt.user; kinit MIT Project Athena (grunt.example.com) Password: &prompt.user; rlogin grunt Last login: Mon May 1 21:14:47 from grumble Copyright (c) 1980, 1983, 1986, 1988, 1990, 1991, 1993, 1994 The Regents of the University of California. All rights reserved. FreeBSD BUILT-19950429 (GR386) #0: Sat Apr 29 17:50:09 SAT 1995 Or Jack logs into Jane's account on the same machine (jane having set up the .klogin file as above, and the person in charge of Kerberos having set up principal jack with a null instance: &prompt.user; kinit &prompt.user; rlogin grunt -l jane MIT Project Athena (grunt.example.com) Password: Last login: Mon May 1 21:16:55 from grumble Copyright (c) 1980, 1983, 1986, 1988, 1990, 1991, 1993, 1994 The Regents of the University of California. All rights reserved. FreeBSD BUILT-19950429 (GR386) #0: Sat Apr 29 17:50:09 SAT 1995 Gary Palmer Contributed by Alex Nash Firewalls firewall security firewalls Firewalls are an area of increasing interest for people who are connected to the Internet, and are even finding applications on private networks to provide enhanced security. This section will hopefully explain what firewalls are, how to use them, and how to use the facilities provided in the FreeBSD kernel to implement them. People often think that having a firewall between your internal network and the Big Bad Internet will solve all your security problems. It may help, but a poorly setup firewall system is more of a security risk than not having one at all. A firewall can add another layer of security to your systems, but it cannot stop a really determined cracker from penetrating your internal network. If you let internal security lapse because you believe your firewall to be impenetrable, you have just made the crackers job that much easier. What Is a Firewall? There are currently two distinct types of firewalls in common use on the Internet today. The first type is more properly called a packet filtering router, where the kernel on a multi-homed machine chooses whether to forward or block packets based on a set of rules. The second type, known as a proxy server, relies on daemons to provide authentication and to forward packets, possibly on a multi-homed machine which has kernel packet forwarding disabled. Sometimes sites combine the two types of firewalls, so that only a certain machine (known as a bastion host) is allowed to send packets through a packet filtering router onto an internal network. Proxy services are run on the bastion host, which are generally more secure than normal authentication mechanisms. FreeBSD comes with a kernel packet filter (known as IPFW), which is what the rest of this section will concentrate on. Proxy servers can be built on FreeBSD from third party software, but there is such a variety of proxy servers available that it would be impossible to cover them in this section. Packet Filtering Routers A router is a machine which forwards packets between two or more networks. A packet filtering router has an extra piece of code in its kernel which compares each packet to a list of rules before deciding if it should be forwarded or not. Most modern IP routing software has packet filtering code within it that defaults to forwarding all packets. To enable the filters, you need to define a set of rules for the filtering code so it can decide if the packet should be allowed to pass or not. To decide whether a packet should be passed on, the code looks through its set of rules for a rule which matches the contents of this packets headers. Once a match is found, the rule action is obeyed. The rule action could be to drop the packet, to forward the packet, or even to send an ICMP message back to the originator. Only the first match counts, as the rules are searched in order. Hence, the list of rules can be referred to as a rule chain. The packet matching criteria varies depending on the software used, but typically you can specify rules which depend on the source IP address of the packet, the destination IP address, the source port number, the destination port number (for protocols which support ports), or even the packet type (UDP, TCP, ICMP, etc). Proxy Servers Proxy servers are machines which have had the normal system daemons (telnetd, ftpd, etc) replaced with special servers. These servers are called proxy servers as they normally only allow onward connections to be made. This enables you to run (for example) a proxy telnet server on your firewall host, and people can telnet in to your firewall from the outside, go through some authentication mechanism, and then gain access to the internal network (alternatively, proxy servers can be used for signals coming from the internal network and heading out). Proxy servers are normally more secure than normal servers, and often have a wider variety of authentication mechanisms available, including one-shot password systems so that even if someone manages to discover what password you used, they will not be able to use it to gain access to your systems as the password instantly expires. As they do not actually give users access to the host machine, it becomes a lot more difficult for someone to install backdoors around your security system. Proxy servers often have ways of restricting access further, so that only certain hosts can gain access to the servers, and often they can be set up so that you can limit which users can talk to which destination machine. Again, what facilities are available depends largely on what proxy software you choose. What Does IPFW Allow Me to Do? ipfw IPFW, the software supplied with FreeBSD, is a packet filtering and accounting system which resides in the kernel, and has a user-land control utility, &man.ipfw.8;. Together, they allow you to define and query the rules currently used by the kernel in its routing decisions. There are two related parts to IPFW. The firewall section allows you to perform packet filtering. There is also an IP accounting section which allows you to track usage of your router, based on similar rules to the firewall section. This allows you to see (for example) how much traffic your router is getting from a certain machine, or how much WWW (World Wide Web) traffic it is forwarding. As a result of the way that IPFW is designed, you can use IPFW on non-router machines to perform packet filtering on incoming and outgoing connections. This is a special case of the more general use of IPFW, and the same commands and techniques should be used in this situation. Enabling IPFW on FreeBSD ipfw enabling As the main part of the IPFW system lives in the kernel, you will need to add one or more options to your kernel configuration file, depending on what facilities you want, and recompile your kernel. See "Reconfiguring your Kernel" () for more details on how to recompile your kernel. There are currently three kernel configuration options relevant to IPFW: options IPFIREWALL Compiles into the kernel the code for packet filtering. options IPFIREWALL_VERBOSE Enables code to allow logging of packets through &man.syslogd.8;. Without this option, even if you specify that packets should be logged in the filter rules, nothing will happen. options IPFIREWALL_VERBOSE_LIMIT=10 Limits the number of packets logged through &man.syslogd.8; on a per entry basis. You may wish to use this option in hostile environments in which you want to log firewall activity, but do not want to be open to a denial of service attack via syslog flooding. When a chain entry reaches the packet limit specified, logging is turned off for that particular entry. To resume logging, you will need to reset the associated counter using the &man.ipfw.8; utility: &prompt.root; ipfw zero 4500 Where 4500 is the chain entry you wish to continue logging. Previous versions of FreeBSD contained an IPFIREWALL_ACCT option. This is now obsolete as the firewall code automatically includes accounting facilities. Configuring IPFW ipfw configuring The configuration of the IPFW software is done through the &man.ipfw.8; utility. The syntax for this command looks quite complicated, but it is relatively simple once you understand its structure. There are currently four different command categories used by the utility: addition/deletion, listing, flushing, and clearing. Addition/deletion is used to build the rules that control how packets are accepted, rejected, and logged. Listing is used to examine the contents of your rule set (otherwise known as the chain) and packet counters (accounting). Flushing is used to remove all entries from the chain. Clearing is used to zero out one or more accounting entries. Altering the IPFW Rules The syntax for this form of the command is: ipfw -N command index action log protocol addresses options There is one valid flag when using this form of the command: -N Resolve addresses and service names in output. The command given can be shortened to the shortest unique form. The valid commands are: add Add an entry to the firewall/accounting rule list delete Delete an entry from the firewall/accounting rule list Previous versions of IPFW used separate firewall and accounting entries. The present version provides packet accounting with each firewall entry. If an index value is supplied, it is used to place the entry at a specific point in the chain. Otherwise, the entry is placed at the end of the chain at an index 100 greater than the last chain entry (this does not include the default policy, rule 65535, deny). The log option causes matching rules to be output to the system console if the kernel was compiled with IPFIREWALL_VERBOSE. Valid actions are: reject Drop the packet, and send an ICMP host or port unreachable (as appropriate) packet to the source. allow Pass the packet on as normal. (aliases: pass and accept) deny Drop the packet. The source is not notified via an ICMP message (thus it appears that the packet never arrived at the destination). count Update packet counters but do not allow/deny the packet based on this rule. The search continues with the next chain entry. Each action will be recognized by the shortest unambiguous prefix. The protocols which can be specified are: all Matches any IP packet icmp Matches ICMP packets tcp Matches TCP packets udp Matches UDP packets The address specification is: from address/maskport to address/maskport via interface You can only specify port in conjunction with protocols which support ports (UDP and TCP). The is optional and may specify the IP address or domain name of a local IP interface, or an interface name (e.g. ed0) to match only packets coming through this interface. Interface unit numbers can be specified with an optional wildcard. For example, ppp* would match all kernel PPP interfaces. The syntax used to specify an address/mask is: address or address/mask-bits or address:mask-pattern A valid hostname may be specified in place of the IP address. is a decimal number representing how many bits in the address mask should be set. e.g. specifying 192.216.222.1/24 will create a mask which will allow any address in a class C subnet (in this case, 192.216.222) to be matched. is an IP address which will be logically AND'ed with the address given. The keyword any may be used to specify any IP address. The port numbers to be blocked are specified as: port,port,port… to specify either a single port or a list of ports, or port-port to specify a range of ports. You may also combine a single range with a list, but the range must always be specified first. The options available are: frag Matches if the packet is not the first fragment of the datagram. in Matches if the packet is on the way in. out Matches if the packet is on the way out. ipoptions spec Matches if the IP header contains the comma separated list of options specified in spec. The supported list of IP options are: ssrr (strict source route), lsrr (loose source route), rr (record packet route), and ts (time stamp). The absence of a particular option may be denoted with a leading !. established Matches if the packet is part of an already established TCP connection (i.e. it has the RST or ACK bits set). You can optimize the performance of the firewall by placing established rules early in the chain. setup Matches if the packet is an attempt to establish a TCP connection (the SYN bit is set but the ACK bit is not). tcpflags flags Matches if the TCP header contains the comma separated list of flags. The supported flags are fin, syn, rst, psh, ack, and urg. The absence of a particular flag may be indicated by a leading !. icmptypes types Matches if the ICMP type is present in the list types. The list may be specified as any combination of ranges and/or individual types separated by commas. Commonly used ICMP types are: 0 echo reply (ping reply), 3 destination unreachable, 5 redirect, 8 echo request (ping request), and 11 time exceeded (used to indicate TTL expiration as with &man.traceroute.8;). Listing the IPFW Rules The syntax for this form of the command is: ipfw -a -t -N l There are three valid flags when using this form of the command: -a While listing, show counter values. This option is the only way to see accounting counters. -t Display the last match times for each chain entry. The time listing is incompatible with the input syntax used by the &man.ipfw.8; utility. -N Attempt to resolve given addresses and service names. Flushing the IPFW Rules The syntax for flushing the chain is: ipfw flush This causes all entries in the firewall chain to be removed except the fixed default policy enforced by the kernel (index 65535). Use caution when flushing rules, the default deny policy will leave your system cut off from the network until allow entries are added to the chain. Clearing the IPFW Packet Counters The syntax for clearing one or more packet counters is: ipfw zero index When used without an index argument, all packet counters are cleared. If an index is supplied, the clearing operation only affects a specific chain entry. Example Commands for <application>ipfw</application> This command will deny all packets from the host evil.crackers.org to the telnet port of the host nice.people.org: &prompt.root; ipfw add deny tcp from evil.crackers.org to nice.people.org 23 The next example denies and logs any TCP traffic from the entire crackers.org network (a class C) to the nice.people.org machine (any port). &prompt.root; ipfw add deny log tcp from evil.crackers.org/24 to nice.people.org If you do not want people sending X sessions to your internal network (a subnet of a class C), the following command will do the necessary filtering: &prompt.root; ipfw add deny tcp from any to my.org/28 6000 setup To see the accounting records: &prompt.root; ipfw -a list or in the short form &prompt.root; ipfw -a l You can also see the last time a chain entry was matched with: &prompt.root; ipfw -at l Building a Packet Filtering Firewall The following suggestions are just that: suggestions. The requirements of each firewall are different and we cannot tell you how to build a firewall to meet your particular requirements. When initially setting up your firewall, unless you have a test bench setup where you can configure your firewall host in a controlled environment, it is strongly recommend you use the logging version of the commands and enable logging in the kernel. This will allow you to quickly identify problem areas and cure them without too much disruption. Even after the initial setup phase is complete, I recommend using the logging for `deny' as it allows tracing of possible attacks and also modification of the firewall rules if your requirements alter. If you use the logging versions of the accept command, it can generate large amounts of log data as one log line will be generated for every packet that passes through the firewall, so large FTP/http transfers, etc, will really slow the system down. It also increases the latencies on those packets as it requires more work to be done by the kernel before the packet can be passed on. syslogd will also start using up a lot more processor time as it logs all the extra data to disk, and it could quite easily fill the partition /var/log is located on. You should enable your firewall from /etc/rc.conf.local or /etc/rc.conf. The associated manual page explains which knobs to fiddle and lists some preset firewall configurations. If you do not use a preset configuration, ipfw list will output the current ruleset into a file that you can pass to rc.conf. If you do not use /etc/rc.conf.local or /etc/rc.conf to enable your firewall, it is important to make sure your firewall is enabled before any IP interfaces are configured. The next problem is what your firewall should actually do! This is largely dependent on what access to your network you want to allow from the outside, and how much access to the outside world you want to allow from the inside. Some general rules are: Block all incoming access to ports below 1024 for TCP. This is where most of the security sensitive services are, like finger, SMTP (mail) and telnet. Block all incoming UDP traffic. There are very few useful services that travel over UDP, and what useful traffic there is, is normally a security threat (e.g. Suns RPC and NFS protocols). This has its disadvantages also, since UDP is a connectionless protocol, denying incoming UDP traffic also blocks the replies to outgoing UDP traffic. This can cause a problem for people (on the inside) using external archie (prospero) servers. If you want to allow access to archie, you will have to allow packets coming from ports 191 and 1525 to any internal UDP port through the firewall. ntp is another service you may consider allowing through, which comes from port 123. Block traffic to port 6000 from the outside. Port 6000 is the port used for access to X11 servers, and can be a security threat (especially if people are in the habit of doing xhost + on their workstations). X11 can actually use a range of ports starting at 6000, the upper limit being how many X displays you can run on the machine. The upper limit as defined by RFC 1700 (Assigned Numbers) is 6063. Check what ports any internal servers use (e.g. SQL servers, etc). It is probably a good idea to block those as well, as they normally fall outside the 1-1024 range specified above. Another checklist for firewall configuration is available from CERT at http://www.cert.org/tech_tips/packet_filtering.html As stated above, these are only guidelines. You will have to decide what filter rules you want to use on your firewall yourself. We cannot accept ANY responsibility if someone breaks into your network, even if you follow the advice given above. IPFW Overhead and Optimization Many people want to know how much overhead IPFW adds to a system. The answer to this depends mostly on your rule set and processor speed. For most applications dealing with Ethernet and small rule sets, the answer is negligible. For those of you that need actual measurements to satisfy your curiosity, read on. The following measurements were made using 2.2.5-STABLE on a 486-66. (While IPFW has changed slightly in later releases of FreeBSD, it still performs with similar speed.) IPFW was modified to measure the time spent within the ip_fw_chk routine, displaying the results to the console every 1000 packets. Two rule sets, each with 1000 rules were tested. The first set was designed to demonstrate a worst case scenario by repeating the rule: &prompt.root; ipfw add deny tcp from any to any 55555 This demonstrates worst case by causing most of IPFW's packet check routine to be executed before finally deciding that the packet does not match the rule (by virtue of the port number). Following the 999th iteration of this rule was an allow ip from any to any. The second set of rules were designed to abort the rule check quickly: &prompt.root; ipfw add deny ip from 1.2.3.4 to 1.2.3.4 The non-matching source IP address for the above rule causes these rules to be skipped very quickly. As before, the 1000th rule was an allow ip from any to any. The per-packet processing overhead in the former case was - approximately 2.703ms/packet, or roughly 2.7 microseconds per + approximately 2.703 ms/packet, or roughly 2.7 microseconds per rule. Thus the theoretical packet processing limit with these - rules is around 370 packets per second. Assuming 10Mbps - Ethernet and a ~1500 byte packet size, we would only be able + rules is around 370 packets per second. Assuming 10 Mbps + Ethernet and a ~1500 byte packet size, we would only be able to achieve a 55.5% bandwidth utilization. For the latter case each packet was processed in - approximately 1.172ms, or roughly 1.2 microseconds per rule. + approximately 1.172 ms, or roughly 1.2 microseconds per rule. The theoretical packet processing limit here would be about - 853 packets per second, which could consume 10Mbps Ethernet + 853 packets per second, which could consume 10 Mbps Ethernet bandwidth. The excessive number of rules tested and the nature of those rules do not provide a real-world scenario -- they were used only to generate the timing information presented here. Here are a few things to keep in mind when building an efficient rule set: Place an established rule early on to handle the majority of TCP traffic. Do not put any allow tcp statements before this rule. Place heavily triggered rules earlier in the rule set than those rarely used (without changing the permissiveness of the firewall, of course). You can see which rules are used most often by examining the packet counting statistics with ipfw -a l. OpenSSL security OpenSSL OpenSSL - As of FreeBSD 4.0, the OpenSSL toolkit is a part of the base + As of FreeBSD 4.0, the OpenSSL toolkit is a part of the base system. OpenSSL provides a general-purpose cryptography library, as well as the Secure Sockets Layer v2/v3 (SSLv2/SSLv3) and Transport Layer Security v1 (TLSv1) network security protocols. However, one of the algorithms (specifically IDEA) included in OpenSSL is protected by patents in the USA and elsewhere, and is not available for unrestricted use. IDEA is included in the OpenSSL sources in FreeBSD, but it is not built by default. If you wish to use it, and you comply with the license terms, enable the MAKE_IDEA switch in /etc/make.conf and rebuild your sources using make world. Today, the RSA algorithm is free for use in USA and other countries. In the past it was protected by a patent. OpenSSL install Source Code Installations OpenSSL is part of the src-crypto and src-secure cvsup collections. See the Obtaining FreeBSD section for more information about obtaining and updating FreeBSD source code. Yoshinobu Inoue Contributed by IPsec IPsec security IPsec Terminating Characters Throughout examples in this section, and other sections, you will notice that there is a ^D at the end of some examples. This means to hold down the Control key and hit the D key. Another commonly used character is ^C, which respectively means to hold down Control and press C. For other HOWTOs detailing IPsec implementation in FreeBSD, take a look at and . The IPsec mechanism provides secure communication for IP layer and socket layer communication. This section should explain how to use them. For implementation details, please refer to The Developers' Handbook. The current IPsec implementation supports both transport mode and tunnel mode. However, tunnel mode comes with some restrictions. http://www.kame.net/newsletter/ has more comprehensive examples. Please be aware that in order to use this functionality, you must have the following options compiled into your kernel: options IPSEC #IP security options IPSEC_ESP #IP security (crypto; define w/IPSEC) Transport Mode Example with IPv4 Let us setup security association to deploy a secure channel between HOST A (10.2.3.4) and HOST B (10.6.7.8). Here we show a little complicated example. From HOST A to HOST B, only old AH is used. From HOST B to HOST A, new AH and new ESP are combined. Now we should choose an algorithm to be used corresponding to AH/new AH/ESP/ new ESP. Please refer to the &man.setkey.8; man page to know algorithm names. Our choice is MD5 for AH, new-HMAC-SHA1 for new AH, and new-DES-expIV with 8 byte IV for new ESP. Key length highly depends on each algorithm. For example, key length must be equal to 16 bytes for MD5, 20 for new-HMAC-SHA1, and 8 for new-DES-expIV. Now we choose MYSECRETMYSECRET, KAMEKAMEKAMEKAMEKAME, PASSWORD, respectively. OK, let us assign SPI (Security Parameter Index) for each protocol. Please note that we need 3 SPIs for this secure channel since three security headers are produced (one for from HOST A to HOST B, two for from HOST B to HOST A). Please also note that SPI MUST be greater than or equal to 256. We choose, 1000, 2000, and 3000, respectively. (1) HOST A ------> HOST B (1)PROTO=AH ALG=MD5(RFC1826) KEY=MYSECRETMYSECRET SPI=1000 (2.1) HOST A <------ HOST B <------ (2.2) (2.1) PROTO=AH ALG=new-HMAC-SHA1(new AH) KEY=KAMEKAMEKAMEKAMEKAME SPI=2000 (2.2) PROTO=ESP ALG=new-DES-expIV(new ESP) IV length = 8 KEY=PASSWORD SPI=3000 Now, let us setup security association. Execute &man.setkey.8; on both HOST A and B: &prompt.root; setkey -c add 10.2.3.4 10.6.7.8 ah-old 1000 -m transport -A keyed-md5 "MYSECRETMYSECRET" ; add 10.6.7.8 10.2.3.4 ah 2000 -m transport -A hmac-sha1 "KAMEKAMEKAMEKAMEKAME" ; add 10.6.7.8 10.2.3.4 esp 3000 -m transport -E des-cbc "PASSWORD" ; ^D Actually, IPsec communication does not process until security policy entries are defined. In this case, you must setup each host. At A: &prompt.root; setkey -c spdadd 10.2.3.4 10.6.7.8 any -P out ipsec ah/transport/10.2.3.4-10.6.7.8/require ; ^D At B: &prompt.root; setkey -c spdadd 10.6.7.8 10.2.3.4 any -P out ipsec esp/transport/10.6.7.8-10.2.3.4/require ; spdadd 10.6.7.8 10.2.3.4 any -P out ipsec ah/transport/10.6.7.8-10.2.3.4/require ; ^D HOST A --------------------------------------> HOST E 10.2.3.4 10.6.7.8 | | ========== old AH keyed-md5 ==========> <========= new AH hmac-sha1 =========== <========= new ESP des-cbc ============ Transport Mode Example with IPv6 Another example using IPv6. ESP transport mode is recommended for TCP port number 110 between Host-A and Host-B. ============ ESP ============ | | Host-A Host-B fec0::10 -------------------- fec0::11 Encryption algorithm is blowfish-cbc whose key is kamekame, and authentication algorithm is hmac-sha1 whose key is this is the test key. Configuration at Host-A: &prompt.root; setkey -c <<EOF spdadd fec0::10[any] fec0::11[110] tcp -P out ipsec esp/transport/fec0::10-fec0::11/use ; spdadd fec0::11[110] fec0::10[any] tcp -P in ipsec esp/transport/fec0::11-fec0::10/use ; add fec0::10 fec0::11 esp 0x10001 -m transport -E blowfish-cbc "kamekame" -A hmac-sha1 "this is the test key" ; add fec0::11 fec0::10 esp 0x10002 -m transport -E blowfish-cbc "kamekame" -A hmac-sha1 "this is the test key" ; EOF and at Host-B: &prompt.root; setkey -c <<EOF spdadd fec0::11[110] fec0::10[any] tcp -P out ipsec esp/transport/fec0::11-fec0::10/use ; spdadd fec0::10[any] fec0::11[110] tcp -P in ipsec esp/transport/fec0::10-fec0::11/use ; add fec0::10 fec0::11 esp 0x10001 -m transport -E blowfish-cbc "kamekame" -A hmac-sha1 "this is the test key" ; add fec0::11 fec0::10 esp 0x10002 -m transport -E blowfish-cbc "kamekame" -A hmac-sha1 "this is the test key" ; EOF Note the direction of SP. Tunnel Mode Example with IPv4 Tunnel mode between two security gateways Security protocol is old AH tunnel mode, i.e. specified by RFC1826, with keyed-md5 whose key is this is the test as authentication algorithm. ======= AH ======= | | Network-A Gateway-A Gateway-B Network-B 10.0.1.0/24 ---- 172.16.0.1 ----- 172.16.0.2 ---- 10.0.2.0/24 Configuration at Gateway-A: &prompt.root; setkey -c <<EOF spdadd 10.0.1.0/24 10.0.2.0/24 any -P out ipsec ah/tunnel/172.16.0.1-172.16.0.2/require ; spdadd 10.0.2.0/24 10.0.1.0/24 any -P in ipsec ah/tunnel/172.16.0.2-172.16.0.1/require ; add 172.16.0.1 172.16.0.2 ah-old 0x10003 -m any -A keyed-md5 "this is the test" ; add 172.16.0.2 172.16.0.1 ah-old 0x10004 -m any -A keyed-md5 "this is the test" ; EOF If the port number field is omitted such as above then [any] is employed. -m specifies the mode of SA to be used. -m any means wild-card of mode of security protocol. You can use this SA for both tunnel and transport mode. and at Gateway-B: &prompt.root; setkey -c <<EOF spdadd 10.0.2.0/24 10.0.1.0/24 any -P out ipsec ah/tunnel/172.16.0.2-172.16.0.1/require ; spdadd 10.0.1.0/24 10.0.2.0/24 any -P in ipsec ah/tunnel/172.16.0.1-172.16.0.2/require ; add 172.16.0.1 172.16.0.2 ah-old 0x10003 -m any -A keyed-md5 "this is the test" ; add 172.16.0.2 172.16.0.1 ah-old 0x10004 -m any -A keyed-md5 "this is the test" ; EOF Making SA bundle between two security gateways AH transport mode and ESP tunnel mode is required between Gateway-A and Gateway-B. In this case, ESP tunnel mode is applied first, and AH transport mode is next. ========== AH ========= | ======= ESP ===== | | | | | Network-A Gateway-A Gateway-B Network-B fec0:0:0:1::/64 --- fec0:0:0:1::1 ---- fec0:0:0:2::1 --- fec0:0:0:2::/64 Tunnel Mode Example with IPv6 Encryption algorithm is 3des-cbc, and authentication algorithm for ESP is hmac-sha1. Authentication algorithm for AH is hmac-md5. Configuration at Gateway-A: &prompt.root; setkey -c <<EOF spdadd fec0:0:0:1::/64 fec0:0:0:2::/64 any -P out ipsec esp/tunnel/fec0:0:0:1::1-fec0:0:0:2::1/require ah/transport/fec0:0:0:1::1-fec0:0:0:2::1/require ; spdadd fec0:0:0:2::/64 fec0:0:0:1::/64 any -P in ipsec esp/tunnel/fec0:0:0:2::1-fec0:0:0:1::1/require ah/transport/fec0:0:0:2::1-fec0:0:0:1::1/require ; add fec0:0:0:1::1 fec0:0:0:2::1 esp 0x10001 -m tunnel -E 3des-cbc "kamekame12341234kame1234" -A hmac-sha1 "this is the test key" ; add fec0:0:0:1::1 fec0:0:0:2::1 ah 0x10001 -m transport -A hmac-md5 "this is the test" ; add fec0:0:0:2::1 fec0:0:0:1::1 esp 0x10001 -m tunnel -E 3des-cbc "kamekame12341234kame1234" -A hmac-sha1 "this is the test key" ; add fec0:0:0:2::1 fec0:0:0:1::1 ah 0x10001 -m transport -A hmac-md5 "this is the test" ; EOF Making SAs with the different end ESP tunnel mode is required between Host-A and Gateway-A. Encryption algorithm is cast128-cbc, and authentication algorithm for ESP is hmac-sha1. ESP transport mode is recommended between Host-A and Host-B. Encryption algorithm is rc5-cbc, and authentication algorithm for ESP is hmac-md5. ================== ESP ================= | ======= ESP ======= | | | | | Host-A Gateway-A Host-B fec0:0:0:1::1 ---- fec0:0:0:2::1 ---- fec0:0:0:2::2 Configuration at Host-A: &prompt.root; setkey -c <<EOF spdadd fec0:0:0:1::1[any] fec0:0:0:2::2[80] tcp -P out ipsec esp/transport/fec0:0:0:1::1-fec0:0:0:2::2/use esp/tunnel/fec0:0:0:1::1-fec0:0:0:2::1/require ; spdadd fec0:0:0:2::1[80] fec0:0:0:1::1[any] tcp -P in ipsec esp/transport/fec0:0:0:2::2-fec0:0:0:l::1/use esp/tunnel/fec0:0:0:2::1-fec0:0:0:1::1/require ; add fec0:0:0:1::1 fec0:0:0:2::2 esp 0x10001 -m transport -E cast128-cbc "12341234" -A hmac-sha1 "this is the test key" ; add fec0:0:0:1::1 fec0:0:0:2::1 esp 0x10002 -E rc5-cbc "kamekame" -A hmac-md5 "this is the test" ; add fec0:0:0:2::2 fec0:0:0:1::1 esp 0x10003 -m transport -E cast128-cbc "12341234" -A hmac-sha1 "this is the test key" ; add fec0:0:0:2::1 fec0:0:0:1::1 esp 0x10004 -E rc5-cbc "kamekame" -A hmac-md5 "this is the test" ; EOF Chern Lee Contributed by OpenSSH OpenSSH security OpenSSH Secure shell is a set of network connectivity tools used to access remote machines securely. It can be used as a direct replacement for rlogin, rsh, rcp, and telnet. Additionally, any other TCP/IP connections can be tunneled/forwarded securely through ssh. ssh encrypts all traffic to effectively eliminate eavesdropping, connection hijacking, and other network-level attacks. OpenSSH is maintained by the OpenBSD project, and is based upon SSH v1.2.12 with all the recent bug fixes and updates. It is compatible with both SSH protocols 1 and 2. OpenSSH has been - in the base system since FreeBSD 4.0. + in the base system since FreeBSD 4.0. Advantages of Using OpenSSH Normally, when using &man.telnet.1; or &man.rlogin.1;, data is sent over the network in an clear, un-encrypted form. Network sniffers anywhere in between the client and server can steal your user/password information or data transferred in your session. OpenSSH offers a variety of authentication and encryption methods to prevent this from happening. Enabling sshd OpenSSH enabling Be sure to make the following additions to your rc.conf file: sshd_enable="YES" This will load the ssh daemon the next time your system initializes. Alternatively, you can simply run the sshd daemon. SSH Client OpenSSH client The &man.ssh.1; utility works similarly to &man.rlogin.1;. &prompt.root; ssh user@example.com Host key not found from the list of known hosts. Are you sure you want to continue connecting (yes/no)? yes Host 'example.com' added to the list of known hosts. user@example.com's password: ******* The login will continue just as it would have if a session was created using rlogin or telnet. SSH utilizes a key fingerprint system for verifying the authenticity of the server when the client connects. The user is prompted to enter yes only when connecting for the first time. Future attempts to login are all verified against the saved fingerprint key. The SSH client will alert you if the saved fingerprint differs from the received fingerprint on future login attempts. The fingerprints are saved in ~/.ssh/known_hosts, or ~/.ssh/known_hosts2 for SSH v2 fingerprints. By default, OpenSSH servers are configured to accept both SSH v1 and SSH v2 connections. The client, however, can choose between the two. Version 2 is known to be more robust and secure than its predecessor. ssh can be forced to use either protocol by passing it the or argument for v1 and v2, respectively. Secure Copy OpenSSH secure copy scp The scp command works similarly to rcp; it copies a file to or from a remote machine, except in a secure fashion. &prompt.root; scp user@example.com:/COPYRIGHT COPYRIGHT user@example.com's password: ******* COPYRIGHT 100% |*****************************| 4735 00:00 &prompt.root; Since the fingerprint was already saved for this host in the previous example, it is verified when using scp here. The arguments passed to scp are similar to cp, with the file or files in the first argument, and the destination in the second. Since the file is fetched over the network, through SSH, one or more of the file arguments takes on the form . Configuration OpenSSH configuration The system-wide configuration files for both the OpenSSH daemon and client reside within the /etc/ssh directory. ssh_config configures the client settings, while sshd_config configures the daemon. Additionally, the (/usr/sbin/sshd by default), and rc.conf options can provide more levels of configuration. ssh-keygen Instead of using passwords, &man.ssh-keygen.1; can be used to generate RSA keys to authenticate a user. &prompt.user; ssh-keygen Initializing random number generator... Generating p: .++ (distance 66) Generating q: ..............................++ (distance 498) Computing the keys... Key generation complete. Enter file in which to save the key (/home/user/.ssh/identity): Enter passphrase: Enter the same passphrase again: Your identification has been saved in /home/user/.ssh/identity. ... &man.ssh-keygen.1; will create a public and private key pair for use in authentication. The private key is stored in ~/.ssh/identity, whereas the public key is stored in ~/.ssh/identity.pub. The public key must be placed in ~/.ssh/authorized_keys of the remote machine in order for the setup to work. This will allow connection to the remote machine based upon RSA authentication instead of passwords. If a passphrase is used in &man.ssh-keygen.1;, the user will be prompted for a password each time in order to use the private key. A SSH v2 DSA key can be created for the same purpose by using the ssh-keygen -d command (or ssh-keygen -t dsa for FreeBSD &os.current;). This will create a public/private DSA key for use in SSH v2 sessions only. The public key is stored in ~/.ssh/id_dsa.pub, while the private key is in ~/.ssh/id_dsa. DSA public keys are placed in ~/.ssh/authorized_keys2 on the remote machine. &man.ssh-agent.1; and &man.ssh-add.1; are utilities used in managing multiple passworded private keys. SSH Tunneling OpenSSH tunneling OpenSSH has the ability to create a tunnel to encapsulate another protocol in an encrypted session. The following command tells &man.ssh.1; to create a tunnel for telnet. &prompt.user; ssh -2 -N -f -L 5023:localhost:23 user@foo.example.com &prompt.user; The ssh command is used with the following options: Forces ssh to use version 2 of the protocol. (Do not use if you are working with older ssh servers) Indicates no command, or tunnel only. If omitted, ssh would initiate a normal session. Forces ssh to run in the background. Indicates a local tunnel in localport:remotehost:remoteport fashion. The remote SSH server. An SSH tunnel works by creating a listen socket on localhost on the specified port. It then forwards any connection received on the local host/port via the SSH connection to the specified remote host and port. In the example, port 5023 on localhost is being forwarded to port 23 on localhost of the remote machine. Since 23 is telnet, this would create a secure telnet session through an SSH tunnel. This can be used to wrap any number of insecure TCP protocols such as SMTP, POP3, FTP, etc. Using SSH to create a secure tunnel for SMTP &prompt.user; ssh -2 -N -f -L 5025:localhost:25 user@mailserver.example.com user@mailserver.example.com's password: ***** &prompt.user; telnet localhost 5025 Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. 220 mailserver.example.com ESMTP This can be used in conjunction with an &man.ssh-keygen.1; and additional user accounts to create a more seamless/hassle-free SSH tunneling environment. Keys can be used in place of typing a password, and the tunnels can be run as a separate user. Practical SSH Tunneling Examples Secure Access of a POP3 server At work, there is an SSH server that accepts connections from the outside. On the same office network resides a mail server running a POP3 server. The network, or network path between your home and office may or may not be completely trustable. Because of this, you need to check your e-mail in a secure manner. The solution is to create an SSH connection to your office's SSH server, and tunnel through to the mail server. &prompt.user; ssh -2 -N -f -L 2110:mail.example.com:110 user@ssh-server.example.com user@ssh-server.example.com's password: ****** When the tunnel is up and running, you can point your mail client to send POP3 requests to localhost port 2110. A connection here will be forwarded securely across the tunnel to mail.example.com. Bypassing a Draconian Firewall Some network administrators impose extremely Draconian firewall rules, filtering not only incoming connections, but outgoing connections. You may be only given access to contact remote machines on ports 22 and 80 for SSH and web surfing. You may wish to access another (perhaps non-work related) service, such as an Ogg Vorbis server to stream music. If this Ogg Vorbis server is streaming on some other port than 22 or 80, you will not be able to access it. The solution is to create an SSH connection to a machine outside of your network's firewall, and use it to tunnel to the Ogg Vorbis server. &prompt.user; ssh -2 -N -f -L 8888:music.example.com:8000 user@unfirewalled.myserver.com user@unfirewalled.myserver.com's password: ******* Your streaming client can now be pointed to localhost port 8888, which will be forwarded over to music.example.com port 8000, successfully evading the firewall. Further Reading OpenSSH &man.ssh.1; &man.scp.1; &man.ssh-keygen.1; &man.ssh-agent.1; &man.ssh-add.1; &man.sshd.8; &man.sftp-server.8; diff --git a/en_US.ISO8859-1/books/handbook/serialcomms/chapter.sgml b/en_US.ISO8859-1/books/handbook/serialcomms/chapter.sgml index 670e2bc290..d1f7e147e7 100644 --- a/en_US.ISO8859-1/books/handbook/serialcomms/chapter.sgml +++ b/en_US.ISO8859-1/books/handbook/serialcomms/chapter.sgml @@ -1,2625 +1,2625 @@ Serial Communications Synopsis serial communications Unix has always had support for serial communications. In fact, the very first Unix machines relied on serial lines for user input and output. Things have changed a lot from the days when the average terminal consisted of a 10-character-per-second serial printer and a keyboard. This chapter will cover some of the ways in which FreeBSD uses serial communications. After reading this chapter, you will know: How to connect terminals to your FreeBSD system. How to use a modem to dial out to remote hosts. How to allow remote users to login to your system with a modem. How to boot your system from a serial console. Before reading this chapter, you should: Know how to configure and install a new kernel (). Understand Unix permissions and processes (). Have access to the technical manual for the serial hardware (modem or multi-port card) that you would like to use with FreeBSD. Introduction Terminology bits-per-second bps Bits per Second — the rate at which data is transmitted DTE DTE Data Terminal Equipment — for example, your computer DCE DCE Data Communications Equipment — your modem RS-232 RS-232C cables EIA standard for hardware serial communications When talking about communications data rates, this section does not use the term baud. Baud refers to the number of electrical state transitions that may be made in a period of time, while bps (bits per second) is the correct term to use (at least it does not seem to bother the curmudgeons quite a much). Cables and Ports To connect a modem or terminal to your FreeBSD system, you will need a serial port on your computer and the proper cable to connect to your serial device. If you are already familiar with your hardware and the cable it requires, you can safely skip this section. Cables There are several different kinds of serial cables. The two most common types for our purposes are null-modem cables and standard ("straight") RS-232 cables. The documentation for your hardware should describe the type of cable required. Null-modem Cables null-modem cable A null-modem cable passes some signals straight through, like signal ground, but switches other signals. For example, the send data pin on one end goes to the receive data pin on the other end. If you like making your own cables, you can construct a null-modem cable for use with terminals. This table shows the RS-232C signal names and the pin numbers on a DB-25 connector. Signal Pin # Pin # Signal TxD 2 connects to 3 RxD RxD 3 connects to 2 TxD DTR 20 connects to 6 DSR DSR 6 connects to 20 DTR SG 7 connects to 7 SG DCD 8 connects to 4 RTS RTS 4 5 CTS CTS 5 connects to 8 DCD For DCD to RTS, connect pins 4 to 5 internally in the connector hood, and then to pin 8 in the remote hood. Standard RS-232C Cables RS-232C cables A standard serial cable passes all the RS-232C signals straight-through. That is, the send data pin on one end of the cable goes to the send data pin on the other end. This is the type of cable to connect a modem to your FreeBSD system, and the type of cable needed for some terminals. Ports Serial ports are the devices through which data is transferred between the FreeBSD host computer and the terminal. This section describes the kinds of ports that exist and how they are addressed in FreeBSD. Kinds of Ports Several kinds of serial ports exist. Before you purchase or construct a cable, you need to make sure it will fit the ports on your terminal and on the FreeBSD system. Most terminals will have DB25 ports. Personal computers, including PCs running FreeBSD, will have DB25 or DB9 ports. If you have a multiport serial card for your PC, you may have RJ-12 or RJ-45 ports. See the documentation that accompanied the hardware for specifications on the kind of port in use. A visual inspection of the port often works too. Port Names In FreeBSD, you access each serial port through an entry in the /dev directory. There are two different kinds of entries: Call-in ports are named /dev/ttydN where N is the port number, starting from zero. Generally, you use the call-in port for terminals. Call-in ports require that the serial line assert the data carrier detect (DCD) signal to work. Call-out ports are named /dev/cuaaN. You usually do not use the call-out port for terminals, just for modems. You may use the call-out port if the serial cable or the terminal does not support the carrier detect signal. If you have connected a terminal to the first serial port (COM1 in MS-DOS), then you want to use /dev/ttyd0 to refer to the terminal. If it is on the second serial port (also known as COM2), it is /dev/ttyd1, and so forth. Kernel Configuration FreeBSD supports four serial ports by default. In the MS-DOS world, these are known as COM1, COM2, COM3, and COM4. FreeBSD currently supports dumb multiport serial interface cards, such as the BocaBoard 1008 and 2016, as well as more intelligent multi-port cards such as those made by Digiboard and Stallion Technologies. However, the default kernel only looks for the standard COM ports. To see if your kernel recognizes any of your serial ports, watch for messages while the kernel is booting, or use the /sbin/dmesg command to replay the kernel's boot messages. In particular, look for messages that start with the characters sio. To view just the messages that have the word sio, use the command: &prompt.root; /sbin/dmesg | grep 'sio' For example, on a system with four serial ports, these are the serial-port specific kernel boot messages: sio0 at 0x3f8-0x3ff irq 4 on isa sio0: type 16550A sio1 at 0x2f8-0x2ff irq 3 on isa sio1: type 16550A sio2 at 0x3e8-0x3ef irq 5 on isa sio2: type 16550A sio3 at 0x2e8-0x2ef irq 9 on isa sio3: type 16550A If your kernel does not recognize all of your serial ports, you will probably need to configure a custom FreeBSD kernel for your system. For detailed information on configuring your kernel, please see . The relevant device lines for your kernel configuration file would look like this: device sio0 at isa? port "IO_COM1" tty irq 4 vector siointr device sio1 at isa? port "IO_COM2" tty irq 3 vector siointr device sio2 at isa? port "IO_COM3" tty irq 5 vector siointr device sio3 at isa? port "IO_COM4" tty irq 9 vector siointr You can comment-out or completely remove lines for devices you do not have. Please see the &man.sio.4; manual page for complete information on how to write configuration lines for multiport boards. Be careful if you are using a configuration file that was previously used for a different version of FreeBSD because the device flags have changed between versions. port "IO_COM1" is a substitution for port 0x3f8, IO_COM2 is 0x2f8, IO_COM3 is 0x3e8, and IO_COM4 is 0x2e8, which are fairly common port addresses for their respective serial ports; interrupts 4, 3, 5, and 9 are fairly common interrupt request lines. Also note that regular serial ports cannot share interrupts on ISA-bus PCs (multiport boards have on-board electronics that allow all the 16550A's on the board to share one or two interrupt request lines). Device Special Files Most devices in the kernel are accessed through device special files, which are located in the /dev directory. The sio devices are accessed through the /dev/ttydN (dial-in) and /dev/cuaaN (call-out) devices. FreeBSD also provides initialization devices (/dev/ttyidN and /dev/cuai0N) and locking devices (/dev/ttyldN and /dev/cual0N). The initialization devices are used to initialize communications port parameters each time a port is opened, such as crtscts for modems which use RTS/CTS signaling for flow control. The locking devices are used to lock flags on ports to prevent users or programs changing certain parameters; see the manual pages &man.termios.4;, &man.sio.4;, and &man.stty.1; for information on the terminal settings, locking and initializing devices, and setting terminal options, respectively. Making Device Special Files - FreeBSD 5.0 includes the devfs + FreeBSD 5.0 includes the devfs filesystem which automatically creates device nodes as needed. If you are running a version of FreeBSD with devfs enabled then you can safely skip this section. A shell script called MAKEDEV in the /dev directory manages the device special files. To use MAKEDEV to make dial-up device special files for COM1 (port 0), cd to /dev and issue the command MAKEDEV ttyd0. Likewise, to make dial-up device special files for COM2 (port 1), use MAKEDEV ttyd1. MAKEDEV not only creates the /dev/ttydN device special files, but also the /dev/cuaaN, /dev/cuaiaN, /dev/cualaN, /dev/ttyldN, and /dev/ttyidN nodes. After making new device special files, be sure to check the permissions on the files (especially the /dev/cua* files) to make sure that only users who should have access to those device special files can read and write on them — you probably do not want to allow your average user to use your modems to dial-out. The default permissions on the /dev/cua* files should be sufficient: crw-rw---- 1 uucp dialer 28, 129 Feb 15 14:38 /dev/cuaa1 crw-rw---- 1 uucp dialer 28, 161 Feb 15 14:38 /dev/cuaia1 crw-rw---- 1 uucp dialer 28, 193 Feb 15 14:38 /dev/cuala1 These permissions allow the user uucp and users in the group dialer to use the call-out devices. Serial Port Configuration ttyd cuaa The ttydN (or cuaaN) device is the regular device you will want to open for your applications. When a process opens the device, it will have a default set of terminal I/O settings. You can see these settings with the command &prompt.root; stty -a -f /dev/ttyd1 When you change the settings to this device, the settings are in effect until the device is closed. When it is reopened, it goes back to the default set. To make changes to the default set, you can open and adjust the settings of the initial state device. For example, to turn on mode, 8 bit communication, and flow control by default for ttyd5, type: &prompt.root; stty -f /dev/ttyid5 clocal cs8 ixon ixoff rc files rc.serial System-wide initialization of the serial devices is controlled in /etc/rc.serial. This file affects the default settings of serial devices. To prevent certain settings from being changed by an application, make adjustments to the lock state device. For example, to lock the speed of - ttyd5 to 57600 bps, type: + ttyd5 to 57600 bps, type: &prompt.root; stty -f /dev/ttyld5 57600 Now, an application that opens ttyd5 and tries to change the speed of - the port will be stuck with 57600 bps. + the port will be stuck with 57600 bps. MAKEDEV Naturally, you should make the initial state and lock state devices writable only by the root account. Sean Kelly Contributed by Terminals terminals Terminals provide a convenient and low-cost way to access your FreeBSD system when you are not at the computer's console or on a connected network. This section describes how to use terminals with FreeBSD. Uses and Types of Terminals The original Unix systems did not have consoles. Instead, people logged in and ran programs through terminals that were connected to the computer's serial ports. It is quite similar to using a modem and terminal software to dial into a remote system to do text-only work. Today's PCs have consoles capable of high quality graphics, but the ability to establish a login session on a serial port still exists in nearly every Unix-style operating system today; FreeBSD is no exception. By using a terminal attached to an unused serial port, you can log in and run any text program that you would normally run on the console or in an xterm window in the X Window System. For the business user, you can attach many terminals to a FreeBSD system and place them on your employees' desktops. For a home user, a spare computer such as an older IBM PC or a Macintosh can be a terminal wired into a more powerful computer running FreeBSD. You can turn what might otherwise be a single-user computer into a powerful multiple user system. For FreeBSD, there are three kinds of terminals: Dumb terminals PCs acting as terminals X terminals The remaining subsections describe each kind. Dumb Terminals Dumb terminals are specialized pieces of hardware that let you connect to computers over serial lines. They are called dumb because they have only enough computational power to display, send, and receive text. You cannot run any programs on them. It is the computer to which you connect them that has all the power to run text editors, compilers, email, games, and so forth. There are hundreds of kinds of dumb terminals made by many manufacturers, including Digital Equipment Corporation's VT-100 and Wyse's WY-75. Just about any kind will work with FreeBSD. Some high-end terminals can even display graphics, but only certain software packages can take advantage of these advanced features. Dumb terminals are popular in work environments where workers do not need access to graphic applications such as those provided by the X Window System. PCs Acting As Terminals If a dumb terminal has just enough ability to display, send, and receive text, then certainly any spare personal computer can be a dumb terminal. All you need is the proper cable and some terminal emulation software to run on the computer. Such a configuration is popular in homes. For example, if your spouse is busy working on your FreeBSD system's console, you can do some text-only work at the same time from a less powerful personal computer hooked up as a terminal to the FreeBSD system. X Terminals X terminals are the most sophisticated kind of terminal available. Instead of connecting to a serial port, they usually connect to a network like Ethernet. Instead of being relegated to text-only applications, they can display any X application. We introduce X terminals just for the sake of completeness. However, this chapter does not cover setup, configuration, or use of X terminals. Configuration This section describes what you need to configure on your FreeBSD system to enable a login session on a terminal. It assumes you have already configured your kernel to support the serial port to which the terminal is connected—and that you have connected it. Recall from that the init process is responsible for all process control and initialization at system startup. One of the tasks performed by init is to read the /etc/ttys file and start a getty process on the available terminals. The getty process is responsible for reading a login name and starting the login program. Thus, to configure terminals for your FreeBSD system the following steps should be taken as root: Add a line to /etc/ttys for the entry in the /dev directory for the serial port if it is not already there. Specify that /usr/libexec/getty be run on the port, and specify the appropriate getty type from the /etc/gettytab file. Specify the default terminal type. Set the port to on. Specify whether the port should be secure. Force init to reread the /etc/ttys file. As an optional step, you may wish to create a custom getty type for use in step 2 by making an entry in /etc/gettytab. This chapter does not explain how to do so; you are encouraged to see the &man.gettytab.5; and the &man.getty.8; manual pages for more information. Adding an Entry to <filename>/etc/ttys</filename> The /etc/ttys file lists all of the ports on your FreeBSD system where you want to allow logins. For example, the first virtual console ttyv0 has an entry in this file. You can log in on the console using this entry. This file also contains entries for the other virtual consoles, serial ports, and pseudo-ttys. For a hardwired terminal, just list the serial port's /dev entry without the /dev part (for example, /dev/ttyv0 would be listed as ttyv0). A default FreeBSD install includes an /etc/ttys file with support for the first four serial ports: ttyd0 through ttyd3. If you are attaching a terminal to one of those ports, you do not need to add another entry. Adding Terminal Entries to <filename>/etc/ttys</filename> Suppose we would like to connect two terminals to the system: a Wyse-50 and an old 286 IBM PC running Procomm terminal software emulating a VT-100 terminal. We connect the Wyse to the second serial port and the 286 to the sixth serial port (a port on a multiport serial card). The corresponding entries in the /etc/ttys file would look like this: ttyd1 "/usr/libexec/getty std.38400" wy50 on insecure ttyd5 "/usr/libexec/getty std.19200" vt100 on insecure The first field normally specifies the name of the terminal special file as it is found in /dev. The second field is the command to execute for this line, which is usually &man.getty.8;. getty initializes and opens the line, sets the speed, prompts for a user name and then executes the &man.login.1; program. The getty program accepts one (optional) parameter on its command line, the getty type. A getty type tells about characteristics on the terminal line, like bps rate and parity. The getty program reads these characteristics from the file /etc/gettytab. The file /etc/gettytab contains lots of entries for terminal lines both old and new. In almost all cases, the entries that start with the text std will work for hardwired terminals. These entries ignore parity. There is a std entry for each bps rate from 110 to 115200. Of course, you can add your own entries to this file. The &man.gettytab.5; manual page provides more information. When setting the getty type in the /etc/ttys file, make sure that the communications settings on the terminal match. For our example, the Wyse-50 uses no parity and - connects at 38400 bps. The 286 PC uses no parity and - connects at 19200 bps. + connects at 38400 bps. The 286 PC uses no parity and + connects at 19200 bps. The third field is the type of terminal usually connected to that tty line. For dial-up ports, unknown or dialup is typically used in this field since users may dial up with practically any type of terminal or software. For hardwired terminals, the terminal type does not change, so you can put a real terminal type from the &man.termcap.5; database file in this field. For our example, the Wyse-50 uses the real terminal type while the 286 PC running Procomm will be set to emulate at VT-100. The fourth field specifies if the port should be enabled. Putting on here will have the init process start the program in the second field, getty. If you put off in this field, there will be no getty, and hence no logins on the port. The final field is used to specify whether the port is secure. Marking a port as secure means that you trust it enough to allow the root account (or any account with a user ID of 0) to login from that port. Insecure ports do not allow root logins. On an insecure port, users must login from unprivileged accounts and then use &man.su.1; or a similar mechanism to gain superuser privileges. It is highly recommended that you use insecure even for terminals that are behind locked doors. It is quite easy to login and use su if you need superuser privileges. Force <command>init</command> to Reread <filename>/etc/ttys</filename> After making the necessary changes to the /etc/ttys file you should send a SIGHUP (hangup) signal to the init process to force it to re-read its configuration file. For example: &prompt.root; kill -HUP 1 init is always the first process run on a system, therefore it will always have PID 1. If everything is set up correctly, all cables are in place, and the terminals are powered up, then a getty process should be running on each terminal and you should see login prompts on your terminals at this point. Troubleshooting Your Connection Even with the most meticulous attention to detail, something could still go wrong while setting up a terminal. Here is a list of symptoms and some suggested fixes. No login prompt appears Make sure the terminal is plugged in and powered up. If it is a personal computer acting as a terminal, make sure it is running terminal emulation software on the correct serial port. Make sure the cable is connected firmly to both the terminal and the FreeBSD computer. Make sure it is the right kind of cable. Make sure the terminal and FreeBSD agree on the bps rate and parity settings. If you have a video display terminal, make sure the contrast and brightness controls are turned up. If it is a printing terminal, make sure paper and ink are in good supply. Make sure that a getty process is running and serving the terminal. For example, to get a list of running getty processes with ps, type: &prompt.root; ps -axww|grep getty You should see an entry for the terminal. For example, the following display shows that a getty is running on the second serial port ttyd1 and is using the std.38400 entry in /etc/gettytab: 22189 d1 Is+ 0:00.03 /usr/libexec/getty std.38400 ttyd1 If no getty process is running, make sure you have enabled the port in /etc/ttys. Also remember to run kill -HUP 1 after modifying the ttys file. If the getty process is running but the terminal still does not display a login prompt, or if it displays a prompt but will not allow you to type, your terminal or cable may not support hardware handshaking. Try changing the entry in /etc/ttys from std.38400 to 3wire.38400 remember to run kill -HUP 1 after modifying /etc/ttys). The 3wire entry is similar to std, but ignores hardware handshaking. You may need to reduce the baud rate or enable software flow control when using 3wire to prevent buffer overflows. Garbage appears instead of a login prompt Make sure the terminal and FreeBSD agree on the bps rate and parity settings. Check the getty processes to make sure the correct getty type is in use. If not, edit /etc/ttys and run kill -HUP 1. Characters appear doubled; the password appears when typed Switch the terminal (or the terminal emulation software) from half duplex or local echo to full duplex. Guy Helmer Contributed by Sean Kelly Additions by Dial-in Service dial-in service Configuring your FreeBSD system for dial-in service is very similar to connecting terminals except that you are dealing with modems instead of terminals. External vs. Internal Modems External modems seem to be more convenient for dial-up, because external modems often can be semi-permanently configured via parameters stored in non-volatile RAM and they usually provide lighted indicators that display the state of important RS-232 signals. Blinking lights impress visitors, but lights are also very useful to see whether a modem is operating properly. Internal modems usually lack non-volatile RAM, so their configuration may be limited only to setting DIP switches. If your internal modem has any signal indicator lights, it is probably difficult to view the lights when the system's cover is in place. Modems and Cables modem If you are using an external modem, then you will of course need the proper cable. A standard RS-232C serial cable should suffice as long as all of the normal signals are wired: Transmitted Data (SD) Received Data (RD) Request to Send (RTS) Clear to Send (CTS) Data Set Ready (DSR) Data Terminal Ready (DTR) Carrier Detect (CD) Signal Ground (SG) FreeBSD needs the RTS and CTS signals for flow-control at speeds above - 2400bps, the CD signal to detect when a call has + 2400 bps, the CD signal to detect when a call has been answered or the line has been hung up, and the DTR signal to reset the modem after a session is complete. Some cables are wired without all of the needed signals, so if you have problems, such as a login session not going away when the line hangs up, you may have a problem with your cable. Like other Unix-like operating systems, FreeBSD uses the hardware signals to find out when a call has been answered or a line has been hung up and to hangup and reset the modem after a call. FreeBSD avoids sending commands to the modem or watching for status reports from the modem. If you are familiar with connecting modems to PC-based bulletin board systems, this may seem awkward. Serial Interface Considerations FreeBSD supports NS8250-, NS16450-, NS16550-, and NS16550A-based EIA RS-232C (CCITT V.24) communications interfaces. The 8250 and 16450 devices have single-character buffers. The 16550 device provides a 16-character buffer, which allows for better system performance. (Bugs in plain 16550's prevent the use of the 16-character buffer, so use 16550A's if possible). Because single-character-buffer devices require more work by the operating system than the 16-character-buffer devices, 16550A-based serial interface cards are much preferred. If the system has many active serial ports or will have a heavy load, 16550A-based cards are better for low-error-rate communications. Quick Overview getty As with terminals, init spawns a getty process for each configured serial port for dial-in connections. For example, if a modem is attached to /dev/ttyd0, the command ps ax might show this: 4850 ?? I 0:00.09 /usr/libexec/getty V19200 ttyd0 When a user dials the modem's line and the modems connect, the CD (Carrier Detect) line is reported by the modem. The kernel notices that carrier has been detected and completes getty's open of the port. getty sends a login: prompt at the specified initial line speed. getty watches to see if legitimate characters are received, and, in a typical configuration, if it finds junk (probably due to the modem's connection speed being different than getty's speed), getty tries adjusting the line speeds until it receives reasonable characters. /usr/bin/login After the user enters his/her login name, getty executes /usr/bin/login, which completes the login by asking for the user's password and then starting the user's shell. Configuration Files There are three system configuration files in the /etc directory that you will probably need to edit to allow dial-up access to your FreeBSD system. The first, /etc/gettytab, contains configuration information for the /usr/libexec/getty daemon. Second, /etc/ttys holds information that tells /sbin/init what tty devices should have getty processes running on them. Lastly, you can place port initialization commands in the /etc/rc.serial script. There are two schools of thought regarding dial-up modems on Unix. One group likes to configure their modems and systems so that no matter at what speed a remote user dials in, the local computer-to-modem RS-232 interface runs at a locked speed. The benefit of this configuration is that the remote user always sees a system login prompt immediately. The downside is that the system does not know what a user's true data rate is, so full-screen programs like Emacs will not adjust their screen-painting methods to make their response better for slower connections. The other school configures their modems' RS-232 interface to vary its speed based on the remote user's connection speed. For example, - V.32bis (14.4 Kbps) connections to the modem might make the modem run - its RS-232 interface at 19.2 Kbps, while 2400 bps connections make the - modem's RS-232 interface run at 2400 bps. Because + V.32bis (14.4 Kbps) connections to the modem might make the modem run + its RS-232 interface at 19.2 Kbps, while 2400 bps connections make the + modem's RS-232 interface run at 2400 bps. Because getty does not understand any particular modem's connection speed reporting, getty gives a login: message at an initial speed and watches the characters that come back in response. If the user sees junk, it is assumed that they know they should press the Enter key until they see a recognizable prompt. If the data rates do not match, getty sees anything the user types as junk, tries going to the next speed and gives the login: prompt again. This procedure can continue ad nauseam, but normally only takes a keystroke or two before the user sees a good prompt. Obviously, this login sequence does not look as clean as the former locked-speed method, but a user on a low-speed connection should receive better interactive response from full-screen programs. This section will try to give balanced configuration information, but is biased towards having the modem's data rate follow the connection rate. <filename>/etc/gettytab</filename> /etc/gettytab /etc/gettytab is a &man.termcap.5;-style file of configuration information for &man.getty.8;. Please see the &man.gettytab.5; manual page for complete information on the format of the file and the list of capabilities. Locked-Speed Config If you are locking your modem's data communications rate at a particular speed, you probably will not need to make any changes to /etc/gettytab. Matching-Speed Config You will need to setup an entry in /etc/gettytab to give getty information about the speeds you wish to - use for your modem. If you have a 2400 bps modem, you can + use for your modem. If you have a 2400 bps modem, you can probably use the existing D2400 entry. # # Fast dialup terminals, 2400/1200/300 rotary (can start either way) # D2400|d2400|Fast-Dial-2400:\ :nx=D1200:tc=2400-baud: 3|D1200|Fast-Dial-1200:\ :nx=D300:tc=1200-baud: 5|D300|Fast-Dial-300:\ :nx=D2400:tc=300-baud: If you have a higher speed modem, you will probably need to add an entry in /etc/gettytab; here is an - entry you could use for a 14.4 Kbps modem with a top interface - speed of 19.2 Kbps: + entry you could use for a 14.4 Kbps modem with a top interface + speed of 19.2 Kbps: # # Additions for a V.32bis Modem # um|V300|High Speed Modem at 300,8-bit:\ :nx=V19200:tc=std.300: un|V1200|High Speed Modem at 1200,8-bit:\ :nx=V300:tc=std.1200: uo|V2400|High Speed Modem at 2400,8-bit:\ :nx=V1200:tc=std.2400: up|V9600|High Speed Modem at 9600,8-bit:\ :nx=V2400:tc=std.9600: uq|V19200|High Speed Modem at 19200,8-bit:\ :nx=V9600:tc=std.19200: This will result in 8-bit, no parity connections. - The example above starts the communications rate at 19.2 Kbps - (for a V.32bis connection), then cycles through 9600 bps (for - V.32), 2400 bps, 1200 bps, 300 bps, and back to 19.2 Kbps. + The example above starts the communications rate at 19.2 Kbps + (for a V.32bis connection), then cycles through 9600 bps (for + V.32), 2400 bps, 1200 bps, 300 bps, and back to 19.2 Kbps. Communications rate cycling is implemented with the nx= (next table) capability. Each of the lines uses a tc= (table continuation) entry to pick up the rest of the standard settings for a particular data rate. - If you have a 28.8 Kbps modem and/or you want to take - advantage of compression on a 14.4 Kbps modem, you need to use a - higher communications rate than 19.2 Kbps. Here is an example of - a gettytab entry starting a 57.6 Kbps: + If you have a 28.8 Kbps modem and/or you want to take + advantage of compression on a 14.4 Kbps modem, you need to use a + higher communications rate than 19.2 Kbps. Here is an example of + a gettytab entry starting a 57.6 Kbps: # # Additions for a V.32bis or V.34 Modem # Starting at 57.6 Kbps # vm|VH300|Very High Speed Modem at 300,8-bit:\ :nx=VH57600:tc=std.300: vn|VH1200|Very High Speed Modem at 1200,8-bit:\ :nx=VH300:tc=std.1200: vo|VH2400|Very High Speed Modem at 2400,8-bit:\ :nx=VH1200:tc=std.2400: vp|VH9600|Very High Speed Modem at 9600,8-bit:\ :nx=VH2400:tc=std.9600: vq|VH57600|Very High Speed Modem at 57600,8-bit:\ :nx=VH9600:tc=std.57600: If you have a slow CPU or a heavily loaded system and do not have 16550A-based serial ports, you may receive sio - silo errors at 57.6 Kbps. + silo errors at 57.6 Kbps. <filename>/etc/ttys</filename> /etc/ttys Configuration of the /etc/ttys file was covered in . Configuration for modems is similar but we must pass a different argument to getty and specify a different terminal type. The general format for both locked-speed and matching-speed configurations is: ttyd0 "/usr/libexec/getty xxx" dialup on The first item in the above line is the device special file for this entry — ttyd0 means /dev/ttyd0 is the file that this getty will be watching. The second item, "/usr/libexec/getty xxx" (xxx will be replaced by the initial gettytab capability) is the process init will run on the device. The third item, dialup, is the default terminal type. The fourth parameter, on, indicates to init that the line is operational. There can be a fifth parameter, secure, but it should only be used for terminals which are physically secure (such as the system console). The default terminal type (dialup in the example above) may depend on local preferences. dialup is the traditional default terminal type on dial-up lines so that users may customize their login scripts to notice when the terminal is dialup and automatically adjust their terminal type. However, the author finds it easier at his site to specify vt102 as the default terminal type, since the users just use VT102 emulation on their remote systems. After you have made changes to /etc/ttys, you may send the init process a HUP signal to re-read the file. You can use the command &prompt.root; kill -HUP 1 to send the signal. If this is your first time setting up the system, you may want to wait until your modem(s) are properly configured and connected before signaling init. Locked-Speed Config For a locked-speed configuration, your ttys entry needs to have a fixed-speed entry provided to getty. For a modem whose port - speed is locked at 19.2 Kbps, the ttys entry + speed is locked at 19.2 Kbps, the ttys entry might look like this: ttyd0 "/usr/libexec/getty std.19200" dialup on If your modem is locked at a different data rate, substitute the appropriate value for std.speed instead of std.19200. Make sure that you use a valid type listed in /etc/gettytab. Matching-Speed Config In a matching-speed configuration, your ttys entry needs to reference the appropriate beginning auto-baud (sic) entry in /etc/gettytab. For example, if you added the above suggested entry for a matching-speed modem that starts at - 19.2 Kbps (the gettytab entry containing the + 19.2 Kbps (the gettytab entry containing the V19200 starting point), your ttys entry might look like this: ttyd0 "/usr/libexec/getty V19200" dialup on <filename>/etc/rc.serial</filename> rc files rc.serial High-speed modems, like V.32, V.32bis, and V.34 modems, need to use hardware (RTS/CTS) flow control. You can add stty commands to /etc/rc.serial to set the hardware flow control flag in the FreeBSD kernel for the modem ports. For example to set the termios flag crtscts on serial port #1's (COM2) dial-in and dial-out initialization devices, the following lines could be added to /etc/rc.serial: # Serial port initial configuration stty -f /dev/ttyid1 crtscts stty -f /dev/cuai01 crtscts Modem Settings If you have a modem whose parameters may be permanently set in non-volatile RAM, you will need to use a terminal program (such as Telix under MS-DOS or tip under FreeBSD) to set the parameters. Connect to the modem using the same communications speed as the initial speed getty will use and configure the modem's non-volatile RAM to match these requirements: CD asserted when connected DTR asserted for operation; dropping DTR hangs up line and resets modem CTS transmitted data flow control Disable XON/XOFF flow control RTS received data flow control Quiet mode (no result codes) No command echo Please read the documentation for your modem to find out what commands and/or DIP switch settings you need to give it. For example, to set the above parameters on a USRobotics Sportster 14,400 external modem, one could give these commands to the modem: ATZ AT&C1&D2&H1&I0&R2&W You might also want to take this opportunity to adjust other settings in the modem, such as whether it will use V.42bis and/or MNP5 compression. The USR Sportster 14,400 external modem also has some DIP switches that need to be set; for other modems, perhaps you can use these settings as an example: Switch 1: UP — DTR Normal Switch 2: N/A (Verbal Result Codes/Numeric Result Codes) Switch 3: UP — Suppress Result Codes Switch 4: DOWN — No echo, offline commands Switch 5: UP — Auto Answer Switch 6: UP — Carrier Detect Normal Switch 7: UP — Load NVRAM Defaults Switch 8: N/A (Smart Mode/Dumb Mode) Result codes should be disabled/suppressed for dial-up modems to avoid problems that can occur if getty mistakenly gives a login: prompt to a modem that is in command mode and the modem echoes the command or returns a result code. This sequence can result in a extended, silly conversation between getty and the modem. Locked-speed Config For a locked-speed configuration, you will need to configure the modem to maintain a constant modem-to-computer data rate independent of the communications rate. On a USR Sportster 14,400 external modem, these commands will lock the modem-to-computer data rate at the speed used to issue the commands: ATZ AT&B1&W Matching-speed Config For a variable-speed configuration, you will need to configure your modem to adjust its serial port data rate to match the incoming call rate. On a USR Sportster 14,400 external modem, these commands will lock the modem's error-corrected data rate to the speed used to issue the commands, but allow the serial port rate to vary for non-error-corrected connections: ATZ AT&B2&W Checking the Modem's Configuration Most high-speed modems provide commands to view the modem's current operating parameters in a somewhat human-readable fashion. On the USR Sportster 14,400 external modems, the command ATI5 displays the settings that are stored in the non-volatile RAM. To see the true operating parameters of the modem (as influenced by the USR's DIP switch settings), use the commands ATZ and then ATI4. If you have a different brand of modem, check your modem's manual to see how to double-check your modem's configuration parameters. Troubleshooting Here are a few steps you can follow to check out the dial-up modem on your system. Checking out the FreeBSD System Hook up your modem to your FreeBSD system, boot the system, and, if your modem has status indication lights, watch to see whether the modem's DTR indicator lights when the login: prompt appears on the system's console — if it lights up, that should mean that FreeBSD has started a getty process on the appropriate communications port and is waiting for the modem to accept a call. If the DTR indicator does not light, login to the FreeBSD system through the console and issue a ps ax to see if FreeBSD is trying to run a getty process on the correct port. You should see lines like these among the processes displayed: 114 ?? I 0:00.10 /usr/libexec/getty V19200 ttyd0 115 ?? I 0:00.10 /usr/libexec/getty V19200 ttyd1 If you see something different, like this: 114 d0 I 0:00.10 /usr/libexec/getty V19200 ttyd0 and the modem has not accepted a call yet, this means that getty has completed its open on the communications port. This could indicate a problem with the cabling or a mis-configured modem, because getty should not be able to open the communications port until CD (carrier detect) has been asserted by the modem. If you do not see any getty processes waiting to open the desired ttydN port, double-check your entries in /etc/ttys to see if there are any mistakes there. Also, check the log file /var/log/messages to see if there are any log messages from init or getty regarding any problems. If there are any messages, triple-check the configuration files /etc/ttys and /etc/gettytab, as well as the appropriate device special files /dev/ttydN, for any mistakes, missing entries, or missing device special files. Try Dialing In Try dialing into the system; be sure to use 8 bits, no parity, and 1 stop bit on the remote system. If you do not get a prompt right away, or get garbage, try pressing Enter about once per second. If you still do not see a login: prompt after a while, try sending a BREAK. If you are using a high-speed modem to do the dialing, try dialing again after locking the dialing modem's interface speed (via AT&B1 on a USR Sportster, for example). If you still cannot get a login: prompt, check /etc/gettytab again and double-check that The initial capability name specified in /etc/ttys for the line matches a name of a capability in /etc/gettytab Each nx= entry matches another gettytab capability name Each tc= entry matches another gettytab capability name If you dial but the modem on the FreeBSD system will not answer, make sure that the modem is configured to answer the phone when DTR is asserted. If the modem seems to be configured correctly, verify that the DTR line is asserted by checking the modem's indicator lights (if it has any). If you have gone over everything several times and it still does not work, take a break and come back to it later. If it still does not work, perhaps you can send an electronic mail message to the &a.questions; describing your modem and your problem, and the good folks on the list will try to help. Dial-out Service dial-out service The following are tips to getting your host to be able to connect over the modem to another computer. This is appropriate for establishing a terminal session with a remote host. This is useful to log onto a BBS. This kind of connection can be extremely helpful to get a file on the Internet if you have problems with PPP. If you need to FTP something and PPP is broken, use the terminal session to FTP it. Then use zmodem to transfer it to your machine. My Stock Hayes Modem Is Not Supported, What Can I Do? Actually, the manual page for tip is out of date. There is a generic Hayes dialer already built in. Just use at=hayes in your /etc/remote file. The Hayes driver is not smart enough to recognize some of the advanced features of newer modems—messages like BUSY, NO DIALTONE, or CONNECT 115200 will just confuse it. You should turn those messages off when you use tip (using ATX0&W). Also, the dial timeout for tip is 60 seconds. Your modem should use something less, or else tip will think there is a communication problem. Try ATS7=45&W. As shipped, tip does not yet support Hayes modems fully. The solution is to edit the file tipconf.h in the directory /usr/src/usr.bin/tip/tip. Obviously you need the source distribution to do this. Edit the line #define HAYES 0 to #define HAYES 1. Then make and make install. Everything works nicely after that. How Am I Expected to Enter These AT Commands? /etc/remote Make what is called a direct entry in your /etc/remote file. For example, if your modem is hooked up to the first serial port, /dev/cuaa0, then put in the following line: cuaa0:dv=/dev/cuaa0:br#19200:pa=none Use the highest bps rate your modem supports in the br capability. Then, type tip cuaa0 and you will be connected to your modem. If there is no /dev/cuaa0 on your system, do this: &prompt.root; cd /dev &prompt.root; sh MAKEDEV cuaa0 Or use cu as root with the following command: &prompt.root; cu -lline -sspeed line is the serial port (e.g./dev/cuaa0) and speed is the speed (e.g.57600). When you are done entering the AT commands hit ~. to exit. The <literal>@</literal> Sign for the pn Capability Does Not Work! The @ sign in the phone number capability tells tip to look in /etc/phones for a phone number. But the @ sign is also a special character in capability files like /etc/remote. Escape it with a backslash: pn=\@ How Can I Dial a Phone Number on the Command Line? Put what is called a generic entry in your /etc/remote file. For example: tip115200|Dial any phone number at 115200 bps:\ :dv=/dev/cuaa0:br#115200:at=hayes:pa=none:du: tip57600|Dial any phone number at 57600 bps:\ :dv=/dev/cuaa0:br#57600:at=hayes:pa=none:du: Then you can do things like: &prompt.root; tip -115200 5551234 If you prefer cu over tip, use a generic cu entry: cu115200|Use cu to dial any number at 115200bps:\ :dv=/dev/cuaa1:br#57600:at=hayes:pa=none:du: and type: &prompt.root; cu 5551234 -s 115200 Do I Have to Type in the bps Rate Every Time I Do That? Put in an entry for tip1200 or cu1200, but go ahead and use whatever bps rate is appropriate with the br capability. tip thinks a - good default is 1200 bps which is why it looks for a - tip1200 entry. You do not have to use 1200 bps, + good default is 1200 bps which is why it looks for a + tip1200 entry. You do not have to use 1200 bps, though. I Access a Number of Hosts through a Terminal Server Rather than waiting until you are connected and typing CONNECT <host> each time, use tip's cm capability. For example, these entries in /etc/remote: pain|pain.deep13.com|Forrester's machine:\ :cm=CONNECT pain\n:tc=deep13: muffin|muffin.deep13.com|Frank's machine:\ :cm=CONNECT muffin\n:tc=deep13: deep13:Gizmonics Institute terminal server:\ :dv=/dev/cuaa2:br#38400:at=hayes:du:pa=none:pn=5551234: will let you type tip pain or tip muffin to connect to the hosts pain or muffin, and tip deep13 to get to the terminal server. Can Tip Try More Than one Line for each Site? This is often a problem where a university has several modem lines and several thousand students trying to use them... Make an entry for your university in /etc/remote and use @ for the pn capability: big-university:\ :pn=\@:tc=dialout dialout:\ :dv=/dev/cuaa3:br#9600:at=courier:du:pa=none: Then, list the phone numbers for the university in /etc/phones: big-university 5551111 big-university 5551112 big-university 5551113 big-university 5551114 tip will try each one in the listed order, then give up. If you want to keep retrying, run tip in a while loop. Why Do I Have to Hit <keycombo action="simul"> <keycap>Ctrl</keycap> <keycap>P</keycap> </keycombo> Twice to Send <keycombo action="simul"> <keycap>Ctrl</keycap> <keycap>P</keycap> </keycombo> Once? CtrlP is the default force character, used to tell tip that the next character is literal data. You can set the force character to any other character with the ~s escape, which means set a variable. Type ~sforce=single-char followed by a newline. single-char is any single character. If you leave out single-char, then the force character is the nul character, which you can get by typing Ctrl2 or CtrlSpace . A pretty good value for single-char is Shift Ctrl 6 , which is only used on some terminal servers. You can have the force character be whatever you want by specifying the following in your $HOME/.tiprc file: force=<single-char> Suddenly Everything I Type Is in UPPER CASE?? You must have pressed Ctrl A , tip's raise character, specially designed for people with broken caps-lock keys. Use ~s as above and set the variable raisechar to something reasonable. In fact, you can set it to the same as the force character, if you never expect to use either of these features. Here is a sample .tiprc file perfect for Emacs users who need to type Ctrl2 and CtrlA a lot: force=^^ raisechar=^^ The ^^ is ShiftCtrl6 . How Can I Do File Transfers with <command>tip</command>? If you are talking to another Unix system, you can send and receive files with ~p (put) and ~t (take). These commands run cat and echo on the remote system to accept and send files. The syntax is: ~p local-file remote-file ~t remote-file local-file There is no error checking, so you probably should use another protocol, like zmodem. How Can I Run zmodem with <command>tip</command>? To receive files, start the sending program on the remote end. Then, type ~C rz to begin receiving them locally. To send files, start the receiving program on the remote end. Then, type ~C sz files to send them to the remote system. Kazutaka YOKOTA Contributed by Bill Paul Based on a document by Setting Up the Serial Console serial console Introduction FreeBSD has the ability to boot on a system with only a dumb terminal on a serial port as a console. Such a configuration should be useful for two classes of people: system administrators who wish to install FreeBSD on machines that have no keyboard or monitor attached, and developers who want to debug the kernel or device drivers. As described in , FreeBSD employs a three stage bootstrap. The first two stages are in the boot block code which is stored at the beginning of the FreeBSD slice on the boot disk. The boot block will then load and run the boot loader (/boot/loader) as the third stage code. In order to set up the serial console you must configure the boot block code, the boot loader code and the kernel. Serial Console Configuration Prepare a serial cable. null-modem cable You will need either a null-modem cable or a standard serial cable and a null-modem adapter. See for a discussion on serial cables. Unplug your keyboard. Most PC systems probe for the keyboard during the Power-On Self-Test (POST) and will generate an error if the keyboard is not detected. Some machines complain loudly about the lack of a keyboard and will not continue to boot until it is plugged in. If your computer complains about the error, but boots anyway, then you do not have to do anything special. (Some machines with Phoenix BIOS installed merely say Keyboard failed and continue to boot normally.) If your computer refuses to boot without a keyboard attached then you will have to configure the BIOS so that it ignores this error (if it can). Consult your motherboard's manual for details on how to do this. Setting the keyboard to Not installed in the BIOS setup does not mean that you will not be able to use your keyboard. All this does is tell the BIOS not to probe for a keyboard at power-on, so it will not complain if the keyboard is not plugged in. You can leave the keyboard plugged in even with this flag set to Not installed and the keyboard will still work. If your system has a PS/2 mouse, chances are very good that you may have to unplug your mouse as well as your keyboard. This is because PS/2 mice share some hardware with the keyboard and leaving the mouse plugged in can fool the keyboard probe into thinking the keyboard is still there. It is said that a - Gateway 2000 Pentium 90MHz system with an AMI BIOS that behaves + Gateway 2000 Pentium 90 MHz system with an AMI BIOS that behaves this way. In general, this is not a problem since the mouse is not much good without the keyboard anyway. Plug a dumb terminal into COM1 (sio0). If you do not have a dumb terminal, you can use an old PC/XT with a modem program, or the serial port on another Unix box. If you do not have a COM1 (sio0), get one. At this time, there is no way to select a port other than COM1 for the boot blocks without recompiling the boot blocks. If you are already using COM1 for another device, you will have to temporarily remove that device and install a new boot block and kernel once you get FreeBSD up and running. (It is assumed that COM1 will be available on a file/compute/terminal server anyway; if you really need COM1 for something else (and you cannot switch that something else to COM2 (sio1)), then you probably should not even be bothering with all this in the first place.) Make sure the configuration file of your kernel has appropriate flags set for COM1 (sio0). Relevant flags are: 0x10 Enables console support for this unit. The other console flags are ignored unless this is set. Currently, at most one unit can have console support; the first one (in config file order) with this flag set is preferred. This option alone will not make the serial port the console. Set the following flag or use the option described below, together with this flag. 0x20 Forces this unit to be the console (unless there is another higher priority console), regardless of the option discussed below. This flag replaces the COMCONSOLE option in FreeBSD versions 2.X. The flag 0x20 must be used together with the flag. 0x40 Reserves this unit (in conjunction with 0x10) and makes the unit unavailable for normal access. You should not set this flag to the serial port unit which you want to use as the serial console. The only use of this flag is to designate the unit for kernel remote debugging. See The Developer's Handbook for more information on remote debugging. - In FreeBSD 4.0 or later the semantics of the + In FreeBSD 4.0 or later the semantics of the flag 0x40 are slightly different and there is another flag to specify a serial port for remote debugging. Example: device sio0 at isa? port "IO_COM1" tty flags 0x10 irq 4 See the &man.sio.4; manual page for more details. If the flags were not set, you need to run UserConfig (on a different console) or recompile the kernel. Create boot.config in the root directory of the a partition on the boot drive. This file will instruct the boot block code how you would like to boot the system. In order to activate the serial console, you need one or more of the following options—if you want multiple options, include them all on the same line: Toggles internal and serial consoles. You can use this to switch console devices. For instance, if you boot from the internal (video) console, you can use to direct the boot loader and the kernel to use the serial port as its console device. Alternatively, if you boot from the serial port, you can use the to tell the boot loader and the kernel to use the video display as the console instead. Toggles single and dual console configurations. In the single configuration the console will be either the internal console (video display) or the serial port, depending on the state of the option above. In the dual console configuration, both the video display and the serial port will become the console at the same time, regardless of the state of the option. However, note that the dual console configuration takes effect only during the boot block is running. Once the boot loader gets control, the console specified by the option becomes the only console. Makes the boot block probe the keyboard. If no keyboard is found, the and options are automatically set. Due to space constraints in the current version of the boot blocks, the option is capable of detecting extended keyboards only. Keyboards with less than 101 keys (and without F11 and F12 keys) may not be detected. Keyboards on some laptop computers may not be properly found because of this limitation. If this is the case with your system, you have to abandon using the option. Unfortunately there is no workaround for this problem. Use either the option to select the console automatically, or the option to activate the serial console. You may include other options described in &man.boot.8; as well. The options, except for , will be passed to the boot loader (/boot/loader). The boot loader will determine which of the internal video or the serial port should become the console by examining the state of the option alone. This means that if you specify the option but not the option in /boot.config, you can use the serial port as the console only during the boot block; the boot loader will use the internal video display as the console. Boot the machine. When you start your FreeBSD box, the boot blocks will echo the contents of /boot.config to the console. For example: /boot.config: -P Keyboard: no The second line appears only if you put in /boot.config and indicates presence/absence of the keyboard. These messages go to either serial or internal console, or both, depending on the option in /boot.config. Options Message goes to none internal console serial console serial and internal consoles serial and internal consoles , keyboard present internal console , keyboard absent serial console After the above messages, there will be a small pause before the boot blocks continue loading the boot loader and before any further messages printed to the console. Under normal circumstances, you do not need to interrupt the boot blocks, but you may want to do so in order to make sure things are set up correctly. Hit any key, other than Enter, at the console to interrupt the boot process. The boot blocks will then prompt you for further action. You should now see something like: >> FreeBSD/i386 BOOT Default: 0:wd(0,a)/boot/loader boot: Verify the above message appears on either the serial or internal console or both, according to the options you put in /boot.config. If the message appears in the correct console, hit Enter to continue the boot process. If you want the serial console but you do not see the prompt on the serial terminal, something is wrong with your settings. In the meantime, you enter and hit Enter/Return (if possible) to tell the boot block (and then the boot loader and the kernel) to choose the serial port for the console. Once the system is up, go back and check what went wrong. After the boot loader is loaded and you are in the third stage of the boot process you can still switch between the internal console and the serial console by setting appropriate environment variables in the boot loader. See . Summary Here is the summary of various settings discussed in this section and the console eventually selected. Case 1: You Set the flags to 0x10 for <devicename>sio0</devicename> device sio0 at isa? port "IO_COM1" tty flags 0x10 irq 4 Options in /boot.config Console during boot blocks Console during boot loader Console in kernel nothing internal internal internal serial serial serial serial and internal internal internal serial and internal serial serial , keyboard present internal internal internal , keyboard absent serial and internal serial serial Case 2: You Set the flags to 0x30 for sio0 device sio0 at isa? port "IO_COM1" tty flags 0x30 irq 4 Options in /boot.config Console during boot blocks Console during boot loader Console in kernel nothing internal internal serial serial serial serial serial and internal internal serial serial and internal serial serial , keyboard present internal internal serial , keyboard absent serial and internal serial serial Tips for the Serial Console Setting a Faster Serial Port Speed By default, the serial port settings are: 9600 baud, 8 bits, no parity, and 1 stop bit. If you wish to change the speed, you need to recompile at least the boot blocks. Add the following line to /etc/make.conf and compile new boot blocks: BOOT_COMCONSOLE_SPEED=19200 If the serial console is configured in some other way than by booting with , or if the serial console used by the kernel is different from the one used by the boot blocks, then you must also add the following option to the kernel configuration file and compile a new kernel: options CONSPEED=19200 Using Serial Port Other Than <devicename>sio0</devicename> for the Console Using a port other than sio0 as the console requires some recompiling. If you want to use another serial port for whatever reasons, recompile the boot blocks, the boot loader and the kernel as follows. Get the kernel source. (See ) Edit /etc/make.conf and set BOOT_COMCONSOLE_PORT to the address of the port you want to use (0x3F8, 0x2F8, 0x3E8 or 0x2E8). Only sio0 through sio3 (COM1 through COM4) can be used; multiport serial cards will not work. No interrupt setting is needed. Create a custom kernel configuration file and add appropriate flags for the serial port you want to use. For example, if you want to make sio1 (COM2) the console: device sio1 at isa? port "IO_COM2" tty flags 0x10 irq 3 or device sio1 at isa? port "IO_COM2" tty flags 0x30 irq 3 The console flags for the other serial ports should not be set. Recompile and install the boot blocks and the boot loader: &prompt.root; cd /sys/boot &prompt.root; make &prompt.root; make install Rebuild and install the kernel. Write the boot blocks to the boot disk with &man.disklabel.8; and boot from the new kernel. Entering the DDB Debugger from the Serial Line If you wish to drop into the kernel debugger from the serial console (useful for remote diagnostics, but also dangerous if you generate a spurious BREAK on the serial port!) then you should compile your kernel with the following options: options BREAK_TO_DEBUGGER options DDB Getting a Login Prompt on the Serial Console While this is not required, you may wish to get a login prompt over the serial line, now that you can see boot messages and can enter the kernel debugging session through the serial console. Here is how to do it. Open the file /etc/ttys with an editor and locate the lines: ttyd0 "/usr/libexec/getty std.9600" unknown off secure ttyd1 "/usr/libexec/getty std.9600" unknown off secure ttyd2 "/usr/libexec/getty std.9600" unknown off secure ttyd3 "/usr/libexec/getty std.9600" unknown off secure ttyd0 through ttyd3 corresponds to COM1 through COM4. Change off to on for the desired port. If you have changed the speed of the serial port, you need to change std.9600 to match the current setting, e.g. std.19200. You may also want to change the terminal type from unknown to the actual type of your serial terminal. After editing the file, you must kill -HUP 1 to make this change take effect. Changing Console from the Boot Loader Previous sections described how to set up the serial console by tweaking the boot block. This section shows that you can specify the console by entering some commands and environment variables in the boot loader. As the boot loader is invoked at the third stage of the boot process, after the boot block, the settings in the boot loader will override the settings in the boot block. Setting up the Serial Console You can easily specify the boot loader and the kernel to use the serial console by writing just one line in /boot/loader.rc: set console=comconsole This will take effect regardless of the settings in the boot block discussed in the previous section. You had better put the above line as the first line of /boot/loader.rc so as to see boot messages on the serial console as early as possible. Likewise, you can specify the internal console as: set console=vidconsole If you do not set the boot loader environment variable console, the boot loader, and subsequently the kernel, will use whichever console indicated by the option in the boot block. In versions 3.2 or later, you may specify the console in /boot/loader.conf.local or /boot/loader.conf, rather than in /boot/loader.rc. In this method your /boot/loader.rc should look like: include /boot/loader.4th start Then, create /boot/loader.conf.local and put the following line there. console=comconsole or console=vidconsole See &man.loader.conf.5; for more information. At the moment, the boot loader has no option equivalent to the option in the boot block, and there is no provision to automatically select the internal console and the serial console based on the presence of the keyboard. Using Serial Port Other than <devicename>sio0</devicename> for the Console You need to recompile the boot loader to use a serial port other than sio0 for the serial console. Follow the procedure described in . Caveats The idea here is to allow people to set up dedicated servers that require no graphics hardware or attached keyboards. Unfortunately, while most systems will let you boot without a keyboard, there are quite a few that will not let you boot without a graphics adapter. Machines with AMI BIOSes can be configured to boot with no graphics adapter installed simply by changing the `graphics adapter' setting in the CMOS configuration to `Not installed.' However, many machines do not support this option and will refuse to boot if you have no display hardware in the system. With these machines, you will have to leave some kind of graphics card plugged in, (even if it is just a junky mono board) although you will not have to attach a monitor into it. You might also try installing an AMI BIOS.