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BillLloydOriginal work by JimMockRewritten by Electronic MailSynopsisemailElectronic Mail, better known as email, is one of the
most widely used forms of communication today. This chapter provides
a basic introduction to running a mail server on &os;, as well as an
introduction to sending and receiving email using &os;; however,
it is not a complete reference and in fact many important
considerations are omitted. For more complete coverage of the
subject, the reader is referred to the many excellent books listed
in .After reading this chapter, you will know:What software components are involved in sending and receiving
electronic mail.Where basic sendmail configuration
files are located in FreeBSD.The difference between remote and
local mailboxes.How to block spammers from illegally using your mail server as a
relay.How to install and configure an alternate Mail Transfer Agent on
your system, replacing sendmail.How to troubleshoot common mail server problems.How to use SMTP with UUCP.How to set up the system to send mail only.How to use mail with a dialup connection.How to configure SMTP Authentication for added security.How to install and use a Mail User Agent, such as
mutt to send and receive email.How to download your mail from a remote POP
or IMAP server.How to automatically apply filters and rules to incoming
email.Before reading this chapter, you should:Properly set up your network connection
().Properly set up the DNS information for your mail host
().Know how to install additional third-party software
().Using Electronic MailPOPIMAPDNSThere are five major parts involved in an email exchange. They
are: the user program, the server daemon, DNS, a
remote or local mailbox, and of course, the
mailhost itself.The User ProgramThis includes command line programs such as
mutt,
alpine, elm,
and mail, and GUI programs such as
balsa,
xfmail to name a few, and something
more sophisticated like a WWW browser. These
programs simply pass off the email transactions to the local
mailhost, either
by calling one of the server
daemons available, or delivering it over TCP.Mailhost Server Daemonmail server daemonssendmailmail server daemonspostfixmail server daemonsqmailmail server daemonsexim&os; ships with sendmail by
default, but also support numerous other mail server daemons,
just some of which include:exim;postfix;qmail.The server daemon usually has two functions—it is responsible
for receiving incoming mail as well as delivering outgoing mail. It is
not responsible for the collection of mail using protocols
such as POP or IMAP to
read your email, nor does it allow connecting to local
mbox or Maildir mailboxes. You may require
an additional daemon for
that.Older versions of sendmail
have some serious security issues which may result in an
attacker gaining local and/or remote access to your machine.
Make sure that you are running a current version to avoid
these problems. Optionally, install an alternative
MTA from the &os;
Ports Collection.Email and DNSThe Domain Name System (DNS) and its daemon
named play a large role in the delivery of
email. In order to deliver mail from your site to another, the
server daemon will look up the remote site in the DNS to determine the
host that will receive mail for the destination. This process
also occurs when mail is sent from a remote host to your mail
server.MX recordDNS is responsible for mapping
hostnames to IP addresses, as well as for storing information
specific to mail delivery, known as MX records. The MX (Mail
eXchanger) record specifies which host, or hosts, will receive
mail for a particular domain. If you do not have an MX record
for your hostname or domain, the mail will be delivered
directly to your host provided you have an A record pointing
your hostname to your IP address.You may view the MX records for any domain by using the
&man.host.1; command, as seen in the example below:&prompt.user; host -t mx FreeBSD.org
FreeBSD.org mail is handled (pri=10) by mx1.FreeBSD.orgReceiving MailemailreceivingReceiving mail for your domain is done by the mail host. It
will collect all mail sent to your domain and store it
either in mbox (the default method for storing mail) or Maildir format, depending
on your configuration.
Once mail has been stored, it may either be read locally using
applications such as &man.mail.1; or
mutt, or remotely accessed and
collected using protocols such as
POP or IMAP.
This means that should you only
wish to read mail locally, you are not required to install a
POP or IMAP server.Accessing remote mailboxes using POP and IMAPPOPIMAPIn order to access mailboxes remotely, you are required to
have access to a POP or IMAP
server. These protocols allow users to connect to their mailboxes from
remote locations with ease. Though both
POP and IMAP allow users
to remotely access mailboxes, IMAP offers
many advantages, some of which are:IMAP can store messages on a remote
server as well as fetch them.IMAP supports concurrent updates.IMAP can be extremely useful over
low-speed links as it allows users to fetch the structure
of messages without downloading them; it can also
perform tasks such as searching on the server in
order to minimize data transfer between clients and
servers.In order to install a POP or
IMAP server, the following steps should be
performed:Choose an IMAP or
POP server that best suits your needs.
The following POP and
IMAP servers are well known and serve
as some good examples:qpopper;teapop;imap-uw;courier-imap;Install the POP or
IMAP daemon of your choosing from the
ports
collection.Where required, modify /etc/inetd.conf
to load the POP or
IMAP server.It should be noted that both POP and
IMAP transmit information, including
username and password credentials in clear-text. This means
that if you wish to secure the transmission of information
across these protocols, you should consider tunneling
sessions over &man.ssh.1;. Tunneling sessions is
described in .Accessing local mailboxesMailboxes may be accessed locally by directly utilizing
MUAs on the server on which the mailbox
resides. This can be done using applications such as
mutt or &man.mail.1;.
The Mail Hostmail hostThe mail host is the name given to a server that is
responsible for delivering and receiving mail for your host, and
possibly your network.ChristopherShumwayContributed by sendmail Configurationsendmail&man.sendmail.8; is the default Mail Transfer Agent (MTA) in
FreeBSD. sendmail's job is to accept
mail from Mail User Agents (MUA) and deliver it
to the appropriate mailer as defined by its configuration file.
sendmail can also accept network
connections and deliver mail to local mailboxes or deliver it to
another program.sendmail uses the following
configuration files:/etc/mail/access/etc/mail/aliases/etc/mail/local-host-names/etc/mail/mailer.conf/etc/mail/mailertable/etc/mail/sendmail.cf/etc/mail/virtusertableFilenameFunction/etc/mail/accesssendmail access database
file/etc/mail/aliasesMailbox aliases/etc/mail/local-host-namesLists of hosts sendmail
accepts mail for/etc/mail/mailer.confMailer program configuration/etc/mail/mailertableMailer delivery table/etc/mail/sendmail.cfsendmail master
configuration file/etc/mail/virtusertableVirtual users and domain tables/etc/mail/accessThe access database defines what host(s) or IP addresses
have access to the local mail server and what kind of access
they have. Hosts can be listed as ,
, or simply passed
to sendmail's error handling routine with a given mailer error.
Hosts that are listed as , which is the
default, are allowed to send mail to this host as long as the
mail's final destination is the local machine. Hosts that are
listed as are rejected for all mail
connections. Hosts that have the option
for their hostname are allowed to send mail for any destination
through this mail server.Configuring the sendmail
Access Databasecyberspammer.com 550 We do not accept mail from spammers
FREE.STEALTH.MAILER@ 550 We do not accept mail from spammers
another.source.of.spam REJECT
okay.cyberspammer.com OK
128.32 RELAYIn this example we have five entries. Mail senders that
match the left hand side of the table are affected by the action
on the right side of the table. The first two examples give an
error code to sendmail's error
handling routine. The message is printed to the remote host when
a mail matches the left hand side of the table. The next entry
rejects mail from a specific host on the Internet,
another.source.of.spam. The next entry accepts
mail connections from a host
okay.cyberspammer.com, which is more exact than
the cyberspammer.com line above. More specific
matches override less exact matches. The last entry allows
relaying of electronic mail from hosts with an IP address that
begins with 128.32. These hosts would be able
to send mail through this mail server that are destined for other
mail servers.When this file is updated, you need to run
make in /etc/mail/ to
update the database./etc/mail/aliasesThe aliases database contains a list of virtual mailboxes
that are expanded to other user(s), files, programs or other
aliases. Here are a few examples that can be used in
/etc/mail/aliases:Mail Aliasesroot: localuser
ftp-bugs: joe,eric,paul
bit.bucket: /dev/null
procmail: "|/usr/local/bin/procmail"The file format is simple; the mailbox name on the left
side of the colon is expanded to the target(s) on the right.
The
first example simply expands the mailbox root
to the mailbox localuser, which is then
looked up again in the aliases database. If no match is found,
then the message is delivered to the local user
localuser. The next example shows a mail
list. Mail to the mailbox ftp-bugs is
expanded to the three local mailboxes joe,
eric, and paul. Note
that a remote mailbox could be specified as user@example.com. The
next example shows writing mail to a file, in this case
/dev/null. The last example shows sending
mail to a program, in this case the mail message is written to the
standard input of /usr/local/bin/procmail
through a &unix; pipe.When this file is updated, you need to run
make in /etc/mail/ to
update the database./etc/mail/local-host-namesThis is a list of hostnames &man.sendmail.8; is to accept as
the local host name. Place any domains or hosts that
sendmail is to be receiving mail for.
For example, if this mail server was to accept mail for the
domain example.com and the host
mail.example.com, its
local-host-names might look something like
this:example.com
mail.example.comWhen this file is updated, &man.sendmail.8; needs to be
restarted to read the changes./etc/mail/sendmail.cfsendmail's master configuration
file, sendmail.cf controls the overall
behavior of sendmail, including everything
from rewriting e-mail addresses to printing rejection messages to
remote mail servers. Naturally, with such a diverse role, this
configuration file is quite complex and its details are a bit
out of the scope of this section. Fortunately, this file rarely
needs to be changed for standard mail servers.The master sendmail configuration
file can be built from &man.m4.1; macros that define the features
and behavior of sendmail. Please see
/usr/src/contrib/sendmail/cf/README for
some of the details.When changes to this file are made,
sendmail needs to be restarted for
the changes to take effect./etc/mail/virtusertableThe virtusertable maps mail addresses for
virtual domains and
mailboxes to real mailboxes. These mailboxes can be local,
remote, aliases defined in
/etc/mail/aliases or files.Example Virtual Domain Mail Maproot@example.com root
postmaster@example.com postmaster@noc.example.net
@example.com joeIn the above example, we have a mapping for a domain
example.com. This file is processed in a
first match order down the file. The first item maps
root@example.com to the local mailbox root. The next entry maps
postmaster@example.com to the mailbox postmaster on the host
noc.example.net. Finally, if nothing from example.com has
matched so far, it will match the last mapping, which matches
every other mail message addressed to someone at
example.com.
This will be mapped to the local mailbox joe.AndrewBoothmanWritten by GregoryNeil ShapiroInformation taken from e-mails written by Changing Your Mail Transfer Agentemailchange mtaAs already mentioned, FreeBSD comes with
sendmail already installed as your
MTA (Mail Transfer Agent). Therefore by default it is
in charge of your outgoing and incoming mail.However, for a variety of reasons, some system
administrators want to change their system's MTA. These
reasons range from simply wanting to try out another MTA to
needing a specific feature or package which relies on another
mailer. Fortunately, whatever the reason, FreeBSD makes it
easy to make the change.Install a New MTAYou have a wide choice of MTAs available. A good
starting point is the
FreeBSD Ports Collection where
you will be able to find many. Of course you are free to use
any MTA you want from any location, as long as you can make
it run under FreeBSD.Start by installing your new MTA. Once it is installed
it gives you a chance to decide if it really fulfills your
needs, and also gives you the opportunity to configure your
new software before getting it to take over from
sendmail. When doing this, you
should be sure that installing the new software will not attempt
to overwrite system binaries such as
/usr/bin/sendmail. Otherwise, your new
mail software has essentially been put into service before
you have configured it.Please refer to your chosen MTA's documentation for
information on how to configure the software you have
chosen.Disable sendmailIf you disable sendmail's
outgoing mail service, it is important that you replace it
with an alternative mail delivery system. If
you choose not to, system functions such as &man.periodic.8;
will be unable to deliver their results by e-mail as they
would normally expect to. Many parts of your system may
expect to have a functional
sendmail-compatible system. If
applications continue to use
sendmail's binaries to try to send
e-mail after you have disabled them, mail could go into an
inactive sendmail queue, and
never be delivered.In order to completely disable
sendmail, including the outgoing
mail service, you must usesendmail_enable="NO"
sendmail_submit_enable="NO"
sendmail_outbound_enable="NO"
sendmail_msp_queue_enable="NO"in /etc/rc.conf.If you only want to disable
sendmail's incoming mail service,
you should setsendmail_enable="NO"in /etc/rc.conf. More information on
sendmail's startup options is
available from the &man.rc.sendmail.8; manual page.Running Your New MTA on BootThe new MTA can be started during boot by adding a
configuration line to /etc/rc.conf
like the following example for postfix:&prompt.root; echo 'postfix_enable=YES' >> /etc/rc.confThe MTA will now be automatically started during
boot.Replacing sendmail as
the System's Default MailerThe program sendmail is so ubiquitous
as standard software on &unix; systems that some software
just assumes it is already installed and configured.
For this reason, many alternative MTA's provide their own compatible
implementations of the sendmail
command-line interface; this facilitates using them as
drop-in replacements for sendmail.Therefore, if you are using an alternative mailer,
you will need to make sure that software trying to execute
standard sendmail binaries such as
/usr/bin/sendmail actually executes
your chosen mailer instead. Fortunately, FreeBSD provides
a system called &man.mailwrapper.8; that does this job for
you.When sendmail is operating as installed, you will
find something like the following
in /etc/mail/mailer.conf:sendmail /usr/libexec/sendmail/sendmail
send-mail /usr/libexec/sendmail/sendmail
mailq /usr/libexec/sendmail/sendmail
newaliases /usr/libexec/sendmail/sendmail
hoststat /usr/libexec/sendmail/sendmail
purgestat /usr/libexec/sendmail/sendmailThis means that when any of these common commands
(such as sendmail itself) are run,
the system actually invokes a copy of mailwrapper named sendmail, which
checks mailer.conf and
executes /usr/libexec/sendmail/sendmail
instead. This system makes it easy to change what binaries
are actually executed when these default sendmail functions
are invoked.Therefore if you wanted
/usr/local/supermailer/bin/sendmail-compat
to be run instead of sendmail, you could change
/etc/mail/mailer.conf to read:sendmail /usr/local/supermailer/bin/sendmail-compat
send-mail /usr/local/supermailer/bin/sendmail-compat
mailq /usr/local/supermailer/bin/mailq-compat
newaliases /usr/local/supermailer/bin/newaliases-compat
hoststat /usr/local/supermailer/bin/hoststat-compat
purgestat /usr/local/supermailer/bin/purgestat-compatFinishingOnce you have everything configured the way you want it, you should
either kill the sendmail processes that
you no longer need and start the processes belonging to your new
software, or simply reboot. Rebooting will also
give you the opportunity to ensure that you have correctly
configured your system to start your new MTA automatically on boot.TroubleshootingemailtroubleshootingWhy do I have to use the FQDN for hosts on my site?You will probably find that the host is actually in a
different domain; for example, if you are in
foo.bar.edu and you wish to reach
a host called mumble in the bar.edu domain, you will have to
refer to it by the fully-qualified domain name, mumble.bar.edu, instead of just
mumble.BINDTraditionally, this was allowed by BSD BIND resolvers.
However the current version of BIND
that ships with FreeBSD no longer provides default abbreviations
for non-fully qualified domain names other than the domain you
are in. So an unqualified host mumble must
either be found as mumble.foo.bar.edu, or it will be searched
for in the root domain.This is different from the previous behavior, where the
search continued across mumble.bar.edu, and mumble.edu. Have a look at RFC 1535
for why this was considered bad practice, or even a security
hole.As a good workaround, you can place the line:
search foo.bar.edu bar.edu
instead of the previous:
domain foo.bar.edu
into your /etc/resolv.conf. However, make
sure that the search order does not go beyond the
boundary between local and public administration,
as RFC 1535 calls it.MX recordsendmail says mail
loops back to myselfThis is answered in the
sendmail FAQ as follows:I'm getting these error messages:
553 MX list for domain.net points back to relay.domain.net
554 <user@domain.net>... Local configuration error
How can I solve this problem?
You have asked mail to the domain (e.g., domain.net) to be
forwarded to a specific host (in this case, relay.domain.net)
by using an MX record, but the relay machine does not recognize
itself as domain.net. Add domain.net to /etc/mail/local-host-names
[known as /etc/sendmail.cw prior to version 8.10]
(if you are using FEATURE(use_cw_file)) or add Cw domain.net
to /etc/mail/sendmail.cf.The sendmail FAQ can be found at
and is
recommended reading if you want to do any
tweaking of your mail setup.PPPHow can I run a mail server on a dial-up PPP host?You want to connect a FreeBSD box on a LAN to the
Internet. The FreeBSD box will be a mail gateway for the LAN.
The PPP connection is non-dedicated.UUCPMX recordThere are at least two ways to do this. One way is to use
UUCP.Another way is to get a full-time Internet server to provide secondary MX
services for your domain. For example, if your company's domain is
example.com and your Internet service provider has
set example.net up to provide secondary MX services
to your domain:example.com. MX 10 example.com.
MX 20 example.net.Only one host should be specified as the final recipient
(add Cw example.com in
/etc/mail/sendmail.cf on example.com).When the sending sendmail is trying to
deliver the mail it will try to connect to you (example.com) over the modem
link. It will most likely time out because you are not online.
The program sendmail will automatically deliver it to the
secondary MX site, i.e. your Internet provider (example.net). The secondary MX
site will then periodically try to connect to
your host and deliver the mail to the primary MX host (example.com).You might want to use something like this as a login
script:#!/bin/sh
# Put me in /usr/local/bin/pppmyisp
( sleep 60 ; /usr/sbin/sendmail -q ) &
/usr/sbin/ppp -direct pppmyispIf you are going to create a separate login script for a
user you could use sendmail -qRexample.com
instead in the script above. This will force all mail in your
queue for example.com to be processed immediately.A further refinement of the situation is as follows:Message stolen from the &a.isp;.> we provide the secondary MX for a customer. The customer connects to
> our services several times a day automatically to get the mails to
> his primary MX (We do not call his site when a mail for his domains
> arrived). Our sendmail sends the mailqueue every 30 minutes. At the
> moment he has to stay 30 minutes online to be sure that all mail is
> gone to the primary MX.
>
> Is there a command that would initiate sendmail to send all the mails
> now? The user has not root-privileges on our machine of course.
In the privacy flags section of sendmail.cf, there is a
definition Opgoaway,restrictqrun
Remove restrictqrun to allow non-root users to start the queue processing.
You might also like to rearrange the MXs. We are the 1st MX for our
customers like this, and we have defined:
# If we are the best MX for a host, try directly instead of generating
# local config error.
OwTrue
That way a remote site will deliver straight to you, without trying
the customer connection. You then send to your customer. Only works for
hosts, so you need to get your customer to name their mail
machine customer.com as well as
hostname.customer.com in the DNS. Just put an A record in
the DNS for customer.com.Why do I keep getting Relaying
Denied errors when sending mail from other
hosts?In default FreeBSD installations,
sendmail is configured to only
send mail from the host it is running on. For example, if
a POP server is available, then users
will be able to check mail from school, work, or other
remote locations but they still will not be able to send
outgoing emails from outside locations. Typically, a few
moments after the attempt, an email will be sent from
MAILER-DAEMON with a
5.7 Relaying Denied error
message.There are several ways to get around this. The most
straightforward solution is to put your ISP's address in
a relay-domains file at
/etc/mail/relay-domains. A quick way
to do this would be:&prompt.root; echo "your.isp.example.com" > /etc/mail/relay-domainsAfter creating or editing this file you must restart
sendmail. This works great if
you are a server administrator and do not wish to send mail
locally, or would like to use a point and click
client/system on another machine or even another ISP. It
is also very useful if you only have one or two email
accounts set up. If there is a large number of addresses
to add, you can simply open this file in your favorite
text editor and then add the domains, one per line:your.isp.example.com
other.isp.example.net
users-isp.example.org
www.example.orgNow any mail sent through your system, by any host in
this list (provided the user has an account on your
system), will succeed. This is a very nice way to allow
users to send mail from your system remotely without
allowing people to send SPAM through your system.Advanced TopicsThe following section covers more involved topics such as mail
configuration and setting up mail for your entire domain.Basic ConfigurationemailconfigurationOut of the box, you should be able to send email to external
hosts as long as you have set up
/etc/resolv.conf or are running your own
name server. If you would like to have mail for your host
delivered to the MTA (e.g., sendmail) on your own FreeBSD host, there are two methods:Run your own name server and have your own domain. For
example, FreeBSD.orgGet mail delivered directly to your host. This is done by
delivering mail directly to the current DNS name for your
machine. For example, example.FreeBSD.org.SMTPRegardless of which of the above you choose, in order to have
mail delivered directly to your host, it must have a permanent
static IP address (not a dynamic address, as with most PPP dial-up configurations). If you are behind a
firewall, it must pass SMTP traffic on to you. If you want to
receive mail directly at your host, you need to be sure of either of two
things:MX recordMake sure that the (lowest-numbered) MX record in your DNS points to your
host's IP address.Make sure there is no MX entry in your DNS for your
host.Either of the above will allow you to receive mail directly at
your host.Try this:&prompt.root; hostname
example.FreeBSD.org
&prompt.root; host example.FreeBSD.org
example.FreeBSD.org has address 204.216.27.XXIf that is what you see, mail directly to
yourlogin@example.FreeBSD.org should work without
problems (assuming sendmail is
running correctly on example.FreeBSD.org).If instead you see something like this:&prompt.root; host example.FreeBSD.org
example.FreeBSD.org has address 204.216.27.XX
example.FreeBSD.org mail is handled (pri=10) by hub.FreeBSD.orgAll mail sent to your host (example.FreeBSD.org) will end up being
collected on hub under the same username instead
of being sent directly to your host.The above information is handled by your DNS server. The DNS
record that carries mail routing information is the
Mail eXchange entry. If
no MX record exists, mail will be delivered directly to the host by
way of its IP address.The MX entry for freefall.FreeBSD.org at one time looked like
this:freefall MX 30 mail.crl.net
freefall MX 40 agora.rdrop.com
freefall MX 10 freefall.FreeBSD.org
freefall MX 20 who.cdrom.comAs you can see, freefall had many MX entries.
The lowest MX number is the host that receives mail directly if
available; if it is not accessible for some reason, the others
(sometimes called backup MXes) accept messages
temporarily, and pass it along when a lower-numbered host becomes
available, eventually to the lowest-numbered host.Alternate MX sites should have separate Internet connections
from your own in order to be most useful. Your ISP or another
friendly site should have no problem providing this service for
you.Mail for Your DomainIn order to set up a mailhost (a.k.a. mail
server) you need to have any mail sent to various workstations
directed to it. Basically, you want to claim any
mail for any hostname in your domain (in this case *.FreeBSD.org) and divert it to your mail
server so your users can receive their mail on
the master mail server.DNSTo make life easiest, a user account with the same
username should exist on both machines. Use
&man.adduser.8; to do this.The mailhost you will be using must be the designated mail
exchanger for each workstation on the network. This is done in
your DNS configuration like so:example.FreeBSD.org A 204.216.27.XX ; Workstation
MX 10 hub.FreeBSD.org ; MailhostThis will redirect mail for the workstation to the mailhost no
matter where the A record points. The mail is sent to the MX
host.You cannot do this yourself unless you are running a DNS
server. If you are not, or cannot run your own DNS server, talk
to your ISP or whoever provides your DNS.If you are doing virtual email hosting, the following
information will come in handy. For this example, we
will assume you have a customer with his own domain, in this
case customer1.org, and you want
all the mail for customer1.org
sent to your mailhost, mail.myhost.com. The entry in your DNS
should look like this:customer1.org MX 10 mail.myhost.comYou do not need an A record for customer1.org if you only
want to handle email for that domain.Be aware that pinging customer1.org will not work unless
an A record exists for it.The last thing that you must do is tell
sendmail on your mailhost what domains
and/or hostnames it should be accepting mail for. There are a few
different ways this can be done. Either of the following will
work:Add the hosts to your
/etc/mail/local-host-names file if you are using the
FEATURE(use_cw_file). If you are using
a version of sendmail earlier than 8.10, the file is
/etc/sendmail.cw.Add a Cwyour.host.com line to your
/etc/sendmail.cf or
/etc/mail/sendmail.cf if you are using
sendmail 8.10 or higher.SMTP with UUCPThe sendmail configuration that ships with FreeBSD is
designed for sites that connect directly to the Internet. Sites
that wish to exchange their mail via UUCP must install another
sendmail configuration file.Tweaking /etc/mail/sendmail.cf manually
is an advanced topic. sendmail version 8 generates config files
via &man.m4.1; preprocessing, where the actual configuration
occurs on a higher abstraction level. The &man.m4.1;
configuration files can be found under
/usr/share/sendmail/cf. The file
README in the cf
directory can serve as a basic introduction to &man.m4.1;
configuration.The best way to support UUCP delivery is to use the
mailertable feature. This creates a database
that sendmail can use to make routing decisions.First, you have to create your .mc
file. The directory
/usr/share/sendmail/cf/cf contains a
few examples. Assuming you have named your file
foo.mc, all you need to do in order to
convert it into a valid sendmail.cf
is:&prompt.root; cd /etc/mail
&prompt.root; make foo.cf
&prompt.root; cp foo.cf /etc/mail/sendmail.cfA typical .mc file might look
like:VERSIONID(`Your version number') OSTYPE(bsd4.4)
FEATURE(accept_unresolvable_domains)
FEATURE(nocanonify)
FEATURE(mailertable, `hash -o /etc/mail/mailertable')
define(`UUCP_RELAY', your.uucp.relay)
define(`UUCP_MAX_SIZE', 200000)
define(`confDONT_PROBE_INTERFACES')
MAILER(local)
MAILER(smtp)
MAILER(uucp)
Cw your.alias.host.name
Cw youruucpnodename.UUCPThe lines containing
accept_unresolvable_domains,
nocanonify, and
confDONT_PROBE_INTERFACES features will
prevent any usage of the DNS during mail delivery. The
UUCP_RELAY clause is needed to support UUCP
delivery. Simply put an Internet hostname there that is able to
handle .UUCP pseudo-domain addresses; most likely, you will
enter the mail relay of your ISP there.Once you have this, you need an
/etc/mail/mailertable file. If you have
only one link to the outside that is used for all your mails,
the following file will suffice:#
# makemap hash /etc/mail/mailertable.db < /etc/mail/mailertable
. uucp-dom:your.uucp.relayA more complex example might look like this:#
# makemap hash /etc/mail/mailertable.db < /etc/mail/mailertable
#
horus.interface-business.de uucp-dom:horus
.interface-business.de uucp-dom:if-bus
interface-business.de uucp-dom:if-bus
.heep.sax.de smtp8:%1
horus.UUCP uucp-dom:horus
if-bus.UUCP uucp-dom:if-bus
. uucp-dom:The first three lines handle special cases where
domain-addressed mail should not be sent out to the default
route, but instead to some UUCP neighbor in order to
shortcut the delivery path. The next line handles
mail to the local Ethernet domain that can be delivered using
SMTP. Finally, the UUCP neighbors are mentioned in the .UUCP
pseudo-domain notation, to allow for a
uucp-neighbor
!recipient
override of the default rules. The last line is always a single
dot, matching everything else, with UUCP delivery to a UUCP
neighbor that serves as your universal mail gateway to the
world. All of the node names behind the
uucp-dom: keyword must be valid UUCP
neighbors, as you can verify using the command
uuname.As a reminder that this file needs to be converted into a
DBM database file before use. The command line to accomplish
this is best placed as a comment at the top of the mailertable file.
You always have to execute this command each time you change
your mailertable file.Final hint: if you are uncertain whether some particular
mail routing would work, remember the
option to sendmail. It starts sendmail in address test
mode; simply enter 3,0, followed
by the address you wish to test for the mail routing. The last
line tells you the used internal mail agent, the destination
host this agent will be called with, and the (possibly
translated) address. Leave this mode by typing CtrlD.&prompt.user; sendmail -bt
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>
>3,0 foo@example.com
canonify input: foo @ example . com
...
parse returns: $# uucp-dom $@ your.uucp.relay $: foo < @ example . com . >
>^DBillMoranContributed by Setting Up to Send OnlyThere are many instances where you may only want to send
mail through a relay. Some examples are:Your computer is a desktop machine, but you want
to use programs such as &man.send-pr.1;. To do so, you should use
your ISP's mail relay.The computer is a server that does not handle mail
locally, but needs to pass off all mail to a relay for
processing.Just about any MTA is capable of filling
this particular niche. Unfortunately, it can be very difficult
to properly configure a full-featured MTA
just to handle offloading mail. Programs such as
sendmail and
postfix are largely overkill for
this use.Additionally, if you are using a typical Internet access
service, your agreement may forbid you from running a
mail server.The easiest way to fulfill those needs is to install the
mail/ssmtp port. Execute
the following commands as root:&prompt.root; cd /usr/ports/mail/ssmtp
&prompt.root; make install replace cleanOnce installed,
mail/ssmtp can be configured
with a four-line file located at
/usr/local/etc/ssmtp/ssmtp.conf:root=yourrealemail@example.com
mailhub=mail.example.com
rewriteDomain=example.com
hostname=_HOSTNAME_Make sure you use your real email address for
root. Enter your ISP's outgoing mail relay
in place of mail.example.com (some ISPs call
this the outgoing mail server or
SMTP server).Make sure you disable sendmail,
including the outgoing mail service. See
for details.mail/ssmtp has some
other options available. See the example configuration file in
/usr/local/etc/ssmtp or the manual page of
ssmtp for some examples and more
information.Setting up ssmtp in this manner
will allow any software on your computer that needs to send
mail to function properly, while not violating your ISP's usage
policy or allowing your computer to be hijacked for spamming.Using Mail with a Dialup ConnectionIf you have a static IP address, you should not need to
adjust anything from the defaults. Set your host name to your
assigned Internet name and sendmail will do the rest.If you have a dynamically assigned IP number and use a
dialup PPP connection to the Internet, you will probably have a
mailbox on your ISPs mail server. Let's assume your ISP's domain
is example.net, and that your
user name is user, you have called your
machine bsd.home, and your ISP has
told you that you may use relay.example.net as a mail relay.In order to retrieve mail from your mailbox, you must
install a retrieval agent. The
fetchmail utility is a good choice as
it supports many different protocols. This program is available
as a package or from the Ports Collection (mail/fetchmail). Usually, your ISP will
provide POP. If you are using user PPP, you can
automatically fetch your mail when an Internet connection is
established with the following entry in
/etc/ppp/ppp.linkup:MYADDR:
!bg su user -c fetchmailIf you are using sendmail (as
shown below) to deliver mail to non-local accounts, you probably
want to have sendmail process your
mailqueue as soon as your Internet connection is established.
To do this, put this command after the
fetchmail command in
/etc/ppp/ppp.linkup: !bg su user -c "sendmail -q"Assume that you have an account for
user on bsd.home. In the home directory of
user on bsd.home, create a
.fetchmailrc file:poll example.net protocol pop3 fetchall pass MySecretThis file should not be readable by anyone except
user as it contains the password
MySecret.In order to send mail with the correct
from: header, you must tell
sendmail to use
user@example.net rather than
user@bsd.home. You may also wish to tell
sendmail to send all mail via relay.example.net, allowing quicker mail
transmission.The following .mc file should
suffice:VERSIONID(`bsd.home.mc version 1.0')
OSTYPE(bsd4.4)dnl
FEATURE(nouucp)dnl
MAILER(local)dnl
MAILER(smtp)dnl
Cwlocalhost
Cwbsd.home
MASQUERADE_AS(`example.net')dnl
FEATURE(allmasquerade)dnl
FEATURE(masquerade_envelope)dnl
FEATURE(nocanonify)dnl
FEATURE(nodns)dnl
define(`SMART_HOST', `relay.example.net')
Dmbsd.home
define(`confDOMAIN_NAME',`bsd.home')dnl
define(`confDELIVERY_MODE',`deferred')dnlRefer to the previous section for details of how to turn
this .mc file into a
sendmail.cf file. Also, do not forget to
restart sendmail after updating
sendmail.cf.JamesGorhamWritten by SMTP AuthenticationHaving SMTP Authentication in place on
your mail server has a number of benefits.
SMTP Authentication can add another layer
of security to sendmail, and has the benefit of giving mobile
users who switch hosts the ability to use the same mail server
without the need to reconfigure their mail client settings
each time.Install security/cyrus-sasl2
from the ports. You can find this port in
security/cyrus-sasl2. The
security/cyrus-sasl2 port
supports a number of compile-time options. For the SMTP
Authentication method we will be using here, make sure that
the option is not disabled.After installing security/cyrus-sasl2,
edit /usr/local/lib/sasl2/Sendmail.conf
(or create it if it does not exist) and add the following
line:pwcheck_method: saslauthdNext, install security/cyrus-sasl2-saslauthd,
edit /etc/rc.conf to add the following
line:saslauthd_enable="YES"and finally start the saslauthd daemon:&prompt.root; /usr/local/etc/rc.d/saslauthd startThis daemon serves as a broker for sendmail to
authenticate against your FreeBSD passwd
database. This saves the trouble of creating a new set of usernames
and passwords for each user that needs to use
SMTP authentication, and keeps the login
and mail password the same.Now edit /etc/make.conf and add the
following lines:SENDMAIL_CFLAGS=-I/usr/local/include/sasl -DSASL
SENDMAIL_LDFLAGS=-L/usr/local/lib
SENDMAIL_LDADD=-lsasl2These lines will give sendmail
the proper configuration options for linking
to cyrus-sasl2 at compile time.
Make sure that cyrus-sasl2
has been installed before recompiling
sendmail.Recompile sendmail by executing the following commands:&prompt.root; cd /usr/src/lib/libsmutil
&prompt.root; make cleandir && make obj && make
&prompt.root; cd /usr/src/lib/libsm
&prompt.root; make cleandir && make obj && make
&prompt.root; cd /usr/src/usr.sbin/sendmail
&prompt.root; make cleandir && make obj && make && make installThe compile of sendmail should not have any problems
if /usr/src has not been changed extensively
and the shared libraries it needs are available.After sendmail has been compiled
and reinstalled, edit your /etc/mail/freebsd.mc
file (or whichever file you use as your .mc file. Many administrators
choose to use the output from &man.hostname.1; as the .mc file for
uniqueness). Add these lines to it:dnl set SASL options
TRUST_AUTH_MECH(`GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN')dnl
define(`confAUTH_MECHANISMS', `GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN')dnlThese options configure the different methods available to
sendmail for authenticating users.
If you would like to use a method other than
pwcheck, please see the
included documentation.Finally, run &man.make.1; while in /etc/mail.
That will run your new .mc file and create a .cf file named
freebsd.cf (or whatever name you have used
for your .mc file). Then use the
command make install restart, which will
copy the file to sendmail.cf, and will
properly restart sendmail.
For more information about this process, you should refer
to /etc/mail/Makefile.If all has gone correctly, you should be able to enter your login
information into the mail client and send a test message.
For further investigation, set the of
sendmail to 13 and watch
/var/log/maillog for any errors.For more information, please see the sendmail
page regarding
SMTP authentication.MarcSilverContributed by Mail User AgentsMail User AgentsA Mail User Agent (MUA) is an application
that is used to send and receive email. Furthermore, as email
evolves and becomes more complex,
MUA's are becoming increasingly powerful in the
way they interact with email; this gives users increased
functionality and flexibility. &os; contains support for
numerous mail user agents, all of which can be easily installed
using the FreeBSD Ports Collection.
Users may choose between graphical email clients such as
evolution or
balsa, console based clients such as
mutt, alpine
or mail, or the web interfaces used by some
large organizations.mail&man.mail.1; is the default Mail User Agent
(MUA) in &os;. It is a
console based MUA that offers all the basic
functionality required to send and receive text-based email,
though it is limited in interaction abilities with attachments
and can only support local mailboxes.Although mail does not natively support
interaction with POP or
IMAP servers, these mailboxes may be
downloaded to a local mbox file using an
application such as fetchmail, which
will be discussed later in this chapter ().In order to send and receive email, simply invoke the
mail command as per the following
example:&prompt.user; mailThe contents of the user mailbox in
/var/mail are
automatically read by the mail utility.
Should the mailbox be empty, the utility exits with a
message indicating that no mails could be found. Once the
mailbox has been read, the application interface is started, and
a list of messages will be displayed. Messages are automatically
numbered, as can be seen in the following example:Mail version 8.1 6/6/93. Type ? for help.
"/var/mail/marcs": 3 messages 3 new
>N 1 root@localhost Mon Mar 8 14:05 14/510 "test"
N 2 root@localhost Mon Mar 8 14:05 14/509 "user account"
N 3 root@localhost Mon Mar 8 14:05 14/509 "sample"Messages can now be read by using the tmail command, suffixed by the message number
that should be displayed. In this example, we will read the
first email:& t 1
Message 1:
From root@localhost Mon Mar 8 14:05:52 2004
X-Original-To: marcs@localhost
Delivered-To: marcs@localhost
To: marcs@localhost
Subject: test
Date: Mon, 8 Mar 2004 14:05:52 +0200 (SAST)
From: root@localhost (Charlie Root)
This is a test message, please reply if you receive it.As can be seen in the example above, the t
key will cause the message to be displayed with full headers.
To display the list of messages again, the h
key should be used.If the email requires a response, you may use
mail to reply, by using either the
R or rmail
keys. The R key instructs
mail to reply only to the sender of the
email, while r replies not only to the sender,
but also to other recipients of the message. You may also
suffix these commands with the mail number which you would like
make a reply to. Once this has been done, the response should
be entered, and the end of the message should be marked by a
single . on a new line. An example can be seen
below:& R 1
To: root@localhost
Subject: Re: test
Thank you, I did get your email.
.
EOTIn order to send new email, the m
key should be used, followed by the
recipient email address. Multiple recipients may also be
specified by separating each address with the ,
delimiter. The subject of the message may then be entered,
followed by the message contents. The end of the message should
be specified by putting a single . on a new
line.& mail root@localhost
Subject: I mastered mail
Now I can send and receive email using mail ... :)
.
EOTWhile inside the mail utility, the
? command may be used to display help at any
time, the &man.mail.1; manual page should also be consulted for
more help with mail.As previously mentioned, the &man.mail.1; command was not
originally designed to handle attachments, and thus deals with
them very poorly. Newer MUAs such as
mutt handle attachments in a much
more intelligent way. But should you still wish to use the
mail command, the converters/mpack port may be of
considerable use.muttmutt is a small yet very
powerful Mail User Agent, with excellent features,
just some of which include:The ability to thread messages;PGP support for digital signing and encryption of
email;MIME Support;Maildir Support;Highly customizable.All of these features help to make
mutt one of the most advanced mail
user agents available. See for more
information on mutt.The stable version of mutt may be
installed using the mail/mutt port, while the current
development version may be installed via the mail/mutt-devel port. After the port
has been installed, mutt can be
started by issuing the following command:&prompt.user; muttmutt will automatically read the
contents of the user mailbox in /var/mail and display the contents
if applicable. If no mails are found in the user mailbox, then
mutt will wait for commands from the
user. The example below shows mutt
displaying a list of messages:In order to read an email, simply select it using the cursor
keys, and press the Enter key. An example of
mutt displaying email can be seen
below:As with the &man.mail.1; command,
mutt allows users to reply only to
the sender of the message as well as to all recipients. To
reply only to the sender of the email, use the
r keyboard shortcut. To send a group reply,
which will be sent to the original sender as well as all the
message recipients, use the g shortcut.mutt makes use of the
&man.vi.1; command as an editor for creating and replying to
emails. This may be customized by the user by creating or
editing their own .muttrc file in their home directory and setting the
editor variable or by setting the
EDITOR environment variable. See
for more
information about configuring
mutt.In order to compose a new mail message, press
m. After a valid subject has been given,
mutt will start &man.vi.1; and the
mail can be written. Once the contents of the mail are
complete, save and quit from vi and
mutt will resume, displaying a
summary screen of the mail that is to be delivered. In order to
send the mail, press y. An example of the
summary screen can be seen below:mutt also contains extensive
help, which can be accessed from most of the menus by pressing
the ? key. The top line also displays the
keyboard shortcuts where appropriate.alpinealpine is aimed at a beginner
user, but also includes some advanced features.The alpine software has had several remote vulnerabilities
discovered in the past, which allowed remote attackers to
execute arbitrary code as users on the local system, by the
action of sending a specially-prepared email. All such
known problems have been fixed, but the
alpine code is written in a very insecure style and the &os;
Security Officer believes there are likely to be other
undiscovered vulnerabilities. You install
alpine at your own risk.
- The current version of pine may
+ The current version of alpine may
be installed using the mail/alpine port. Once the port has
installed, alpine can be started by
issuing the following command:&prompt.user; alpineThe first time that alpine is run
it displays a greeting page with a brief introduction, as well
as a request from the alpine
development team to send an anonymous email message allowing
them to judge how many users are using their client. To send
this anonymous message, press Enter, or
alternatively press E to exit the greeting
without sending an anonymous message. An example of the
greeting page can be seen below:Users are then presented with the main menu, which can be
easily navigated using the cursor keys. This main menu provides
shortcuts for the composing new mails, browsing of mail directories,
and even the administration of address book entries. Below the
main menu, relevant keyboard shortcuts to perform functions
specific to the task at hand are shown.The default directory opened by alpine
is the inbox. To view the message index, press
I, or select the MESSAGE INDEX
option as seen below:The message index shows messages in the current directory,
and can be navigated by using the cursor keys. Highlighted
messages can be read by pressing the
Enter key.In the screenshot below, a sample message is displayed by
alpine. Keyboard shortcuts are
displayed as a reference at the bottom of the screen. An
example of one of these shortcuts is the r key,
which tells the MUA to reply to the current
message being displayed.Replying to an email in alpine is
done using the pico editor, which is
installed by default with alpine.
The pico utility makes it easy to
navigate around the message and is slightly more forgiving on
novice users than &man.vi.1; or &man.mail.1;. Once the reply
is complete, the message can be sent by pressing
CtrlX. The alpine application
will ask for confirmation.The alpine application can be
customized using the SETUP option from the main
menu. Consult
for more information.MarcSilverContributed by Using fetchmailfetchmailfetchmail is a full-featured
IMAP and POP client which
allows users to automatically download mail from remote
IMAP and POP servers and
save it into local mailboxes; there it can be accessed more easily.
fetchmail can be installed using the
mail/fetchmail port, and
offers various features, some of which include:Support of POP3,
APOP, KPOP,
IMAP, ETRN and
ODMR protocols.Ability to forward mail using SMTP, which
allows filtering, forwarding, and aliasing to function
normally.May be run in daemon mode to check periodically for new
messages.Can retrieve multiple mailboxes and forward them based
on configuration, to different local users.While it is outside the scope of this document to explain
all of fetchmail's features, some
basic features will be explained. The
fetchmail utility requires a
configuration file known as .fetchmailrc,
in order to run correctly. This file includes server information
as well as login credentials. Due to the sensitive nature of the
contents of this file, it is advisable to make it readable only by the owner,
with the following command:&prompt.user; chmod 600 .fetchmailrcThe following .fetchmailrc serves as an
example for downloading a single user mailbox using
POP. It tells
fetchmail to connect to example.com using a username of
joesoap and a password of
XXX. This example assumes that the user
joesoap is also a user on the local
system.poll example.com protocol pop3 username "joesoap" password "XXX"The next example connects to multiple POP
and IMAP servers and redirects to different
local usernames where applicable:poll example.com proto pop3:
user "joesoap", with password "XXX", is "jsoap" here;
user "andrea", with password "XXXX";
poll example2.net proto imap:
user "john", with password "XXXXX", is "myth" here;The fetchmail utility can be run in daemon
mode by running it with the flag, followed
by the interval (in seconds) that
fetchmail should poll servers listed
in the .fetchmailrc file. The following
example would cause fetchmail to poll
every 600 seconds:&prompt.user; fetchmail -d 600More information on fetchmail can
be found at .MarcSilverContributed by Using procmailprocmailThe procmail utility is an
incredibly powerful application used to filter incoming mail.
It allows users to define rules which can be
matched to incoming mails to perform specific functions or to
reroute mail to alternative mailboxes and/or email addresses.
procmail can be installed using the
mail/procmail port. Once
installed, it can be directly integrated into most
MTAs; consult your MTA
documentation for more information. Alternatively,
procmail can be integrated by adding
the following line to a .forward in the home
directory of the user utilizing
procmail features:"|exec /usr/local/bin/procmail || exit 75"The following section will display some basic
procmail rules, as well as brief
descriptions on what they do. These rules, and others must be
inserted into a .procmailrc file, which
must reside in the user's home directory.The majority of these rules can also be found in the
&man.procmailex.5; manual page.Forward all mail from user@example.com to an
external address of goodmail@example2.com::0
* ^From.*user@example.com
! goodmail@example2.comForward all mails shorter than 1000 bytes to an external
address of goodmail@example2.com::0
* < 1000
! goodmail@example2.comSend all mail sent to alternate@example.com
into a mailbox called alternate::0
* ^TOalternate@example.com
alternateSend all mail with a subject of Spam to
/dev/null::0
^Subject:.*Spam
/dev/nullA useful recipe that parses incoming &os;.org mailing lists
and places each list in its own mailbox::0
* ^Sender:.owner-freebsd-\/[^@]+@FreeBSD.ORG
{
LISTNAME=${MATCH}
:0
* LISTNAME??^\/[^@]+
FreeBSD-${MATCH}
}
diff --git a/en_US.ISO8859-1/books/handbook/serialcomms/chapter.sgml b/en_US.ISO8859-1/books/handbook/serialcomms/chapter.sgml
index 3dcad5284e..30b635913a 100644
--- a/en_US.ISO8859-1/books/handbook/serialcomms/chapter.sgml
+++ b/en_US.ISO8859-1/books/handbook/serialcomms/chapter.sgml
@@ -1,2934 +1,2934 @@
Serial CommunicationsSynopsisserial 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.IntroductionAs of &os; 8.0, device nodes for serial ports have been
renamed from
/dev/cuadN to
/dev/cuauN and
from
/dev/ttydN to
/dev/ttyuN.
&os; 7.X users will have to adapt the following
documentation according to these changes.Terminologybits-per-secondbpsBits per Second — the rate at which data is
transmittedDTEDTEData Terminal Equipment — for example, your
computerDCEDCEData Communications Equipment — your modemRS-232RS-232C cablesEIA standard for hardware serial communicationsWhen 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 as much).Cables and PortsTo 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.CablesThere 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 Cablesnull-modem cableA null-modem cable passes some signals, such as
Signal Ground, straight through, but switches other
signals. For example, the Transmitted Data pin on
one end goes to the Received Data pin on the other
end.You can also construct your own null-modem cable for use with
terminals (e.g., for quality purposes). This table shows the
RS-232C signals
and the pin numbers on a DB-25 connector. Note that the standard
also calls for a straight-through pin 1 to pin 1
Protective Ground line, but it is often
omitted. Some terminals work OK using only pins 2, 3 and 7,
while others require different configurations than the examples
shown below.
When one pin at one end connects to a pair of pins
at the other end, it is usually implemented with one short
wire between the pair of pins in their connector and a
long wire to the other single pin.The above designs seems to be the most popular. In another
variation (explained in the book RS-232 Made
Easy) SG connects to SG, TD connects to RD, RTS and
CTS connect to DCD, DTR connects to DSR, and vice-versa.Standard RS-232C CablesRS-232C cablesA standard serial cable passes all of the RS-232C signals
straight through. That is, the Transmitted Data
pin on one end of the cable goes to the
Transmitted Data pin on the other end. This is
the type of cable to use to connect a modem to your FreeBSD
system, and is also appropriate for some terminals.PortsSerial 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 PortsSeveral 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 DB-25 ports. Personal computers,
including PCs running FreeBSD, will have DB-25 or DB-9 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 NamesIn 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/ttyuN
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 correctly.Call-out ports are named
/dev/cuauN.
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 will
use /dev/ttyu0 to refer to the terminal. If
the terminal is on the second serial port (also known as
COM2), use
/dev/ttyu1, and so forth.Kernel ConfigurationFreeBSD 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 16550AIf your kernel does not recognize all of your serial
ports, you will probably need to configure your kernel
in the /boot/device.hints file. You can
also comment-out or completely remove lines for devices you do not
have.Please refer to the &man.sio.4; manual page for
more information on serial ports and multiport boards configuration.
Be careful if you are using a configuration
file that was previously used for a different version of
FreeBSD because the device flags and the syntax have changed between
- versions.
+ 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 FilesMost 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/ttyuN (dial-in)
and /dev/cuauN
(call-out) devices. FreeBSD also provides initialization devices
(/dev/ttyuN.init and
/dev/cuauN.init)
and
locking devices
(/dev/ttyuN.lock and
/dev/cuauN.lock).
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.Serial Port ConfigurationttyucuauThe ttyuN (or
cuauN) 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/ttyu1When 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
ttyu5, type:&prompt.root; stty -f /dev/ttyu5.init clocal cs8 ixon ixoffrc filesrc.serialSystem-wide initialization of the serial devices is
controlled in /etc/rc.d/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
ttyu5 to 57600 bps, type:&prompt.root; stty -f /dev/ttyu5.lock 57600Now, an application that opens
ttyu5 and tries to change the speed of
the port will be stuck with 57600 bps.Naturally, you should make the initial state and lock state devices
writable only by the root account.SeanKellyContributed by TerminalsAs of &os; 8.0, device nodes for serial ports have been
renamed from
/dev/cuadN to
/dev/cuauN and
from
/dev/ttydN to
/dev/ttyuN.
&os; 7.X users will have to adapt the following
documentation according to these changes.terminalsTerminals 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 TerminalsThe 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 terminalsPCs acting as terminalsX terminalsThe remaining subsections describe each kind.Dumb TerminalsDumb 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 graphical applications such as those provided by
the X Window System.PCs Acting as TerminalsIf 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.There are at least two utilities in the base-system of
&os; that can be used to work through a serial connection:
&man.cu.1; and &man.tip.1;.To connect from a client system that runs &os; to the
serial connection of another system, you can use:&prompt.root; cu -l serial-port-deviceWhere serial-port-device is the name of a
special device file denoting a serial port of your system.
These device files are called
/dev/cuauN.The N-part of a device name is the serial
port number.Note that device numbers in &os; start from zero and not
one (like they do, for instance in &ms-dos;-derived systems).
This means that what &ms-dos;-based systems call
COM1 is usually
/dev/cuau0 in &os;.Some people prefer to use other programs, available
through the Ports Collection. The Ports include quite a few
utilities which can work in ways similar to &man.cu.1; and
&man.tip.1;,
i.e. comms/minicom.X TerminalsX 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.ConfigurationThis 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 /etc/ttysThe /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: ttyu0 through
ttyu3. If you are attaching a terminal
to one of those ports, you do not need to add another entry.Adding Terminal Entries to
/etc/ttysSuppose 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:ttyu1 "/usr/libexec/getty std.38400" wy50 on insecure
ttyu5 "/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 configures
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.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 init to Reread
/etc/ttysAfter 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 1init 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 ConnectionEven 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 AppearsMake 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 gettyYou should see an entry for the terminal. For
example, the following display shows that a
getty is running on the second serial
port ttyu1 and is using the
std.38400 entry in
/etc/gettytab:22189 d1 Is+ 0:00.03 /usr/libexec/getty std.38400 ttyu1If 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.If Garbage Appears Instead of a Login PromptMake 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
TypedSwitch the terminal (or the terminal emulation software)
from half duplex or local echo to
full duplex.GuyHelmerContributed by SeanKellyAdditions by Dial-in ServiceAs of &os; 8.0, device nodes for serial ports have been
renamed from
/dev/cuadN to
/dev/cuauN and
from
/dev/ttydN to
/dev/ttyuN.
&os; 7.X users will have to adapt the following
documentation according to these changes.dial-in serviceConfiguring 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 ModemsExternal 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 CablesmodemIf 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:
Signal NamesAcronymsNamesRDReceived DataTDTransmitted DataDTRData Terminal ReadyDSRData Set ReadyDCDData Carrier Detect (RS-232's Received Line
Signal Detector)SGSignal GroundRTSRequest to SendCTSClear to Send
FreeBSD needs the RTS and
CTS signals for flow control at speeds above
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 ConsiderationsFreeBSD 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 OverviewgettyAs 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/ttyu0, the command
ps ax might show this: 4850 ?? I 0:00.09 /usr/libexec/getty V19200 ttyu0When 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/loginAfter 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 FilesThere 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.d/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 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./etc/gettytab/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 ConfigIf 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 ConfigYou will need to set up 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
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:#
# 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. 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:#
# 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
siosilo errors at 57.6 Kbps./etc/ttys/etc/ttysConfiguration 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:ttyu0 "/usr/libexec/getty xxx" dialup onThe first item in the above line is the device special file for
this entry — ttyu0 means
/dev/ttyu0 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 ConfigFor 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 might look like this:ttyu0 "/usr/libexec/getty std.19200" dialup onIf 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 ConfigIn 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 V19200 starting point), your
ttys entry might look like this:ttyu0 "/usr/libexec/getty V19200" dialup on/etc/rc.d/serialrc filesrc.serialHigh-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.d/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.d/serial:# Serial port initial configuration
stty -f /dev/ttyu1.init crtscts
stty -f /dev/cuau1.init crtsctsModem SettingsIf 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 connectedDTR asserted for operation; dropping DTR
hangs up line and resets modemCTS transmitted data flow controlDisable XON/XOFF flow controlRTS received data flow controlQuiet mode (no result codes)No command echoPlease 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&WYou 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 &usrobotics; &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 NormalSwitch 2: N/A (Verbal Result Codes/Numeric Result
Codes)Switch 3: UP — Suppress Result CodesSwitch 4: DOWN — No echo, offline commandsSwitch 5: UP — Auto AnswerSwitch 6: UP — Carrier Detect NormalSwitch 7: UP — Load NVRAM DefaultsSwitch 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 ConfigFor 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 &usrobotics; &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&WMatching-speed ConfigFor 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 &usrobotics; &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&WChecking the Modem's ConfigurationMost high-speed modems provide commands to view the modem's
current operating parameters in a somewhat human-readable fashion.
On the &usrobotics; &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 modem'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.TroubleshootingHere are a few steps you can follow to check out the dial-up modem
on your system.Checking Out the FreeBSD SystemHook 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 ttyu0
115 ?? I 0:00.10 /usr/libexec/getty V19200 ttyu1If you see something different, like this: 114 d0 I 0:00.10 /usr/libexec/getty V19200 ttyu0and 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
ttyuN 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/ttyuN, for any
mistakes, missing entries, or missing device special files.Try Dialing InTry 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 &usrobotics;
&sportster; modem, for example).If you still cannot get a login: prompt, check
/etc/gettytab again and double-check
thatThe initial capability name specified in
/etc/ttys for the line matches a name of a
capability in /etc/gettytabEach nx= entry matches another
gettytab capability nameEach tc= entry matches another
gettytab capability nameIf 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 ServiceAs of &os; 8.0, device nodes for serial ports have been
renamed from
/dev/cuadN to
/dev/cuauN.
&os; 7.X users will have to adapt the following
documentation according to these changes.dial-out serviceThe following are tips for 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.How Am I Expected to Enter These AT Commands?/etc/remoteMake 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/cuau0,
then put in the following line:cuau0:dv=/dev/cuau0:br#19200:pa=noneUse the highest bps rate your modem supports in the br capability.
Then, type tip cuau0 and you will be connected to
your modem.Or use cu as root with the
following command:&prompt.root; cu -lline -sspeedline is the serial port
(e.g./dev/cuau0) and
speed is the speed
(e.g.57600). When you are done entering the AT
commands type ~. to exit.The @ 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/cuau0:br#115200:at=hayes:pa=none:du:
tip57600|Dial any phone number at 57600 bps:\
:dv=/dev/cuau0:br#57600:at=hayes:pa=none:du:Then you can do things like:&prompt.root; tip -115200 5551234If you prefer cu over tip,
use a generic cu entry:cu115200|Use cu to dial any number at 115200bps:\
:dv=/dev/cuau1:br#57600:at=hayes:pa=none:du:and type:&prompt.root; cu 5551234 -s 115200Do 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, though.I Access a Number of Hosts Through a Terminal ServerRather 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/cuau2: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/cuau3: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 5551114tip 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
CtrlP
Twice to Send
CtrlP
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
ShiftCtrl6, 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-charSuddenly Everything I Type Is in Upper Case??You must have pressed
CtrlA, 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 tip?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:~plocal-fileremote-file~tremote-filelocal-fileThere is no error checking, so you probably should use another
protocol, like zmodem.How Can I Run zmodem with tip?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.KazutakaYOKOTAContributed by BillPaulBased on a document by Setting Up the Serial ConsoleAs of &os; 8.0, device nodes for serial ports have been
renamed from
/dev/ttydN to
/dev/ttyuN.
&os; 7.X users will have to adapt the following
documentation according to these changes.serial consoleIntroductionFreeBSD 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, Terse VersionThis section assumes that you are using the default setup
and just want a fast overview of setting up the serial
console.Connect the serial cable to COM1 and
the controlling terminal.To see all boot messages on the serial console, issue
the following command while logged in as the superuser:&prompt.root; echo 'console="comconsole"' >> /boot/loader.confEdit /etc/ttys and change
off to on and
dialup to vt100 for the
ttyu0 entry. Otherwise a password will
not be required to connect via the serial console, resulting in a
potential security hole.Reboot the system to see if the changes took effect.If a different configuration is required, a more in depth
configuration explanation exists in
.Serial Console ConfigurationPrepare a serial cable.null-modem cableYou 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.Set the keyboard to Not installed in the
BIOS setup. You will still
be able to use your keyboard. All this does is tell the BIOS
not to probe for a keyboard at power-on. Your BIOS should not
complain if the keyboard is absent. You can leave the
keyboard plugged in even with this flag set to Not
installed and the keyboard will still work. If the
above option is not present in the BIOS, look for an
Halt on Error option instead. Setting this to
All but Keyboard or even to
No Errors, will have the same effect.If your system has a &ps2; mouse, chances are very good that
you may have to unplug your mouse as well as your keyboard.
This is because &ps2; 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 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:0x10Enables 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.0x20Forces this unit to be the console (unless there is
another higher priority console), regardless of the
option discussed below.
The flag 0x20 must be used
together with the flag.0x40Reserves 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.Example:device sio0 flags 0x10See 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: noThe 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.OptionsMessage goes tononeinternal consoleserial consoleserial and internal consolesserial and internal consoles, keyboard presentinternal console, keyboard absentserial consoleAfter 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:ad(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 or 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 .SummaryHere is the summary of various settings discussed in this section
and the console eventually selected.Case 1: You Set the Flags to 0x10 for
sio0device sio0 flags 0x10Options in /boot.configConsole during boot blocksConsole during boot loaderConsole in kernelnothinginternalinternalinternalserialserialserialserial and internalinternalinternalserial and internalserialserial, keyboard presentinternalinternalinternal, keyboard absentserial and internalserialserialCase 2: You Set the Flags to 0x30 for sio0device sio0 flags 0x30Options in /boot.configConsole during boot blocksConsole during boot loaderConsole in kernelnothinginternalinternalserialserialserialserialserial and internalinternalserialserial and internalserialserial, keyboard presentinternalinternalserial, keyboard absentserial and internalserialserialTips for the Serial ConsoleSetting a Faster Serial Port SpeedBy default, the serial port settings are: 9600 baud, 8
bits, no parity, and 1 stop bit. If you wish to change the default
console speed, you have the following options:Recompile the boot blocks
with BOOT_COMCONSOLE_SPEED set to the new
console speed. See for
detailed instructions about building and installing new boot
blocks.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=19200Use the boot option of the kernel.
The command line option can be added
to /boot.config. See the &man.boot.8;
manual page for a description of how to add options
to /boot.config and a list of the supported
options.Enable the comconsole_speed
option in your /boot/loader.conf
file.This option depends on console,
boot_serial, and
boot_multicons being set in
/boot/loader.conf too. An example of using
comconsole_speed to change the serial console
speed is:boot_multicons="YES"
boot_serial="YES"
comconsole_speed="115200"
console="comconsole,vidconsole"Using Serial Port Other Than sio0 for
the ConsoleUsing 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 flags 0x10ordevice sio1 flags 0x30The 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 clean
&prompt.root; make
&prompt.root; make installRebuild and install the kernel.Write the boot blocks to the boot disk with
&man.bsdlabel.8; and boot from the new kernel.Entering the DDB Debugger from the Serial LineIf 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 DDBGetting a Login Prompt on the Serial ConsoleWhile 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:ttyu0 "/usr/libexec/getty std.9600" unknown off secure
ttyu1 "/usr/libexec/getty std.9600" unknown off secure
ttyu2 "/usr/libexec/getty std.9600" unknown off secure
ttyu3 "/usr/libexec/getty std.9600" unknown off securettyu0 through
ttyu3 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 LoaderPrevious 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 ConsoleYou can easily specify the boot loader and the kernel to use the
serial console by writing just one line in
/boot/loader.conf: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.conf 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.The console can be specified in
/boot/loader.conf.local or in
/boot/loader.conf.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 a Serial Port Other Than sio0 for
the ConsoleYou need to recompile the boot loader to use a serial port other
than sio0 for the serial console. Follow the
procedure described in .CaveatsThe 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. You might also try installing an AMI
BIOS.