diff --git a/en_US.ISO8859-1/books/handbook/boot/chapter.sgml b/en_US.ISO8859-1/books/handbook/boot/chapter.sgml index 1ed33153cd..5869a106ba 100644 --- a/en_US.ISO8859-1/books/handbook/boot/chapter.sgml +++ b/en_US.ISO8859-1/books/handbook/boot/chapter.sgml @@ -1,1004 +1,1004 @@ The FreeBSD Booting Process Synopsis booting bootstrap The process of starting a computer and loading the operating system is referred to as the bootstrap process, or simply booting. FreeBSD's boot process provides a great deal of flexibility in customizing what happens when you start the system, allowing you to select from different operating systems installed on the same computer, or even different versions of the same operating system or installed kernel. This chapter details the configuration options you can set and how to customize the FreeBSD boot process. This includes everything that happens until the FreeBSD kernel has started, probed for devices, and started &man.init.8;. If you are not quite sure when this happens, it occurs when the text color changes from bright white to grey. After reading this chapter, you will know: What the components of the FreeBSD bootstrap system are, and how they interact. The options you can give to the components in the FreeBSD bootstrap to control the boot process. The basics of &man.device.hints.5;. x86 Only This chapter only describes the boot process for FreeBSD running on Intel x86 systems. The Booting Problem Turning on a computer and starting the operating system poses an interesting dilemma. By definition, the computer does not know how to do anything until the operating system is started. This includes running programs from the disk. So if the computer can not run a program from the disk without the operating system, and the operating system programs are on the disk, how is the operating system started? This problem parallels one in the book The Adventures of Baron Munchausen. A character had fallen part way down a manhole, and pulled himself out by grabbing his bootstraps, and lifting. In the early days of computing the term bootstrap was applied to the mechanism used to load the operating system, which has become shortened to booting. BIOS Basic Input/Output SystemBIOS On x86 hardware the Basic Input/Output System (BIOS) is responsible for loading the operating system. To do this, the BIOS looks on the hard disk for the Master Boot Record (MBR), which must be located on a specific place on the disk. The BIOS has enough knowledge to load and run the MBR, and assumes that the MBR can then carry out the rest of the tasks involved in loading the operating system, possibly with the help of the BIOS. Master Boot Record (MBR) Boot Manager Boot Loader The code within the MBR is usually referred to as a boot manager, especially when it interacts with the user. In this case the boot manager usually has more code in the first track of the disk or within some OS's file system. (A boot manager is sometimes also called a boot loader, but FreeBSD uses that term for a later stage of booting.) Popular boot managers include boot0 (a.k.a. Boot Easy, the standard &os; boot manager), Grub, GAG, and LILO. (Only boot0 fits within the MBR.) If you have only one operating system installed on your disks then a standard PC MBR will suffice. This MBR searches for the first bootable (a.k.a. active) slice on the disk, and then runs the code on that slice to load the remainder of the operating system. The MBR installed by &man.fdisk.8;, by default, is such an MBR. It is based on /boot/mbr. If you have installed multiple operating systems on your disks then you can install a different boot manager, one that can display a list of different operating systems, and allows you to choose the one to boot from. Two of these are discussed in the next subsection. The remainder of the FreeBSD bootstrap system is divided into three stages. The first stage is run by the MBR, which knows just enough to get the computer into a specific state and run the second stage. The second stage can do a little bit more, before running the third stage. The third stage finishes the task of loading the operating system. The work is split into these three stages because the PC standards put limits on the size of the programs that can be run at stages one and two. Chaining the tasks together allows FreeBSD to provide a more flexible loader. kernel init The kernel is then started and it begins to probe for devices and initialize them for use. Once the kernel boot process is finished, the kernel passes control to the user process &man.init.8;, which then makes sure the disks are in a usable state. &man.init.8; then starts the user-level resource configuration which mounts file systems, sets up network cards to communicate on the network, and generally starts all the processes that usually are run on a FreeBSD system at startup. The Boot Manager and Boot Stages Boot Manager The Boot Manager Master Boot Record (MBR) The code in the MBR or boot manager is sometimes referred to as stage zero of the boot process. This subsection discusses two of the boot managers previously mentioned: boot0 and LILO. The <application>boot0</application> Boot Manager: The MBR installed by FreeBSD's installer or &man.boot0cfg.8;, by default, is based on /boot/boot0. (The boot0 program is very simple, since the program in the MBR can only be 446 bytes long because of the slice table and 0x55AA identifier at the end of the MBR.) If you have installed boot0 and multiple operating systems on your hard disks, then you will see a display similar to this one at boot time: <filename>boot0</filename> Screenshot F1 DOS F2 FreeBSD F3 Linux F4 ?? F5 Drive 1 Default: F2 Other operating systems, in particular &windows;, have been known to overwrite an existing MBR with their own. If this happens to you, or you want to replace your existing MBR with the FreeBSD MBR then use the following command: &prompt.root; fdisk -B -b /boot/boot0 device where device is the device that you boot from, such as ad0 for the first IDE disk, ad2 for the first IDE disk on a second IDE controller, da0 for the first SCSI disk, and so on. Or, if you want a custom configuration of the MBR, use &man.boot0cfg.8;. The LILO Boot Manager: To install this boot manager so it will also boot FreeBSD, first start Linux and add the following to your existing /etc/lilo.conf configuration file: other=/dev/hdXY table=/dev/hdX loader=/boot/chain.b label=FreeBSD In the above, specify FreeBSD's primary partition and drive using Linux specifiers, replacing X with the Linux drive letter and Y with the Linux primary partition number. If you are using a SCSI drive, you will need to change /dev/hd to read something similar to /dev/sd. The line can be omitted if you have both operating systems on the same drive. Now run /sbin/lilo -v to commit your new changes to the system; this should be verified by checking its screen messages. Stage One, <filename>/boot/boot1</filename>, and Stage Two, <filename>/boot/boot2</filename> Conceptually the first and second stages are part of the same program, on the same area of the disk. Because of space constraints they have been split into two, but you would always install them together. They are copied from the combined file /boot/boot by the installer or bsdlabel (see below). They are located outside file systems, in the first track of the boot slice, starting with the first sector. This is where boot0, or any other boot manager, expects to find a program to run which will continue the boot process. The number of sectors used is easily determined from the size of /boot/boot. boot1 is very simple, since it can only be 512 bytes in size, and knows just enough about the FreeBSD bsdlabel, which stores information about the slice, to find and execute boot2. boot2 is slightly more sophisticated, and understands the FreeBSD file system enough to find files on it, and can provide a simple interface to choose the kernel or loader to run. Since the loader is much more sophisticated, and provides a nice easy-to-use boot configuration, boot2 usually runs it, but previously it was tasked to run the kernel directly. <filename>boot2</filename> Screenshot >> FreeBSD/i386 BOOT Default: 0:ad(0,a)/boot/loader boot: If you ever need to replace the installed boot1 and boot2 use &man.bsdlabel.8;: &prompt.root; bsdlabel -B diskslice where diskslice is the disk and slice you boot from, such as ad0s1 for the first slice on the first IDE disk. Dangerously Dedicated Mode If you use just the disk name, such as ad0, in the &man.bsdlabel.8; command you will create a dangerously dedicated disk, without slices. This is almost certainly not what you want to do, so make sure you double check the &man.bsdlabel.8; command before you press Return. Stage Three, <filename>/boot/loader</filename> boot-loader The loader is the final stage of the three-stage bootstrap, and is located on the file system, usually as /boot/loader. The loader is intended as a user-friendly method for configuration, using an easy-to-use built-in command set, backed up by a more powerful interpreter, with a more complex command set. Loader Program Flow During initialization, the loader will probe for a console and for disks, and figure out what disk it is booting from. It will set variables accordingly, and an interpreter is started where user commands can be passed from a script or interactively. loader loader configuration The loader will then read /boot/loader.rc, which by default reads in /boot/defaults/loader.conf which sets reasonable defaults for variables and reads /boot/loader.conf for local changes to those variables. loader.rc then acts on these variables, loading whichever modules and kernel are selected. Finally, by default, the loader issues a 10 second wait for key presses, and boots the kernel if it is not interrupted. If interrupted, the user is presented with a prompt which understands the easy-to-use command set, where the user may adjust variables, unload all modules, load modules, and then finally boot or reboot. Loader Built-In Commands These are the most commonly used loader commands. For a complete discussion of all available commands, please see &man.loader.8;. autoboot seconds Proceeds to boot the kernel if not interrupted within the time span given, in seconds. It displays a countdown, and the default time span is 10 seconds. boot -options kernelname Immediately proceeds to boot the kernel, with the given options, if any, and with the kernel name given, if it is. Providing a kernel name on the command-line is only applicable after an unload command has been issued, otherwise the previously-loaded kernel will be used. boot-conf Goes through the same automatic configuration of modules based on variables as what happens at boot. This only makes sense if you use unload first, and change some variables, most commonly kernel. help topic Shows help messages read from /boot/loader.help. If the topic given is index, then the list of available topics is given. include filename … Processes the file with the given filename. The file is read in, and interpreted line by line. An error immediately stops the include command. load type filename Loads the kernel, kernel module, or file of the type given, with the filename given. Any arguments after filename are passed to the file. ls path Displays a listing of files in the given path, or the root directory, if the path is not specified. If is specified, file sizes will be shown too. lsdev Lists all of the devices from which it may be possible to load modules. If is specified, more details are printed. lsmod Displays loaded modules. If is specified, more details are shown. more filename Displays the files specified, with a pause at each LINES displayed. reboot Immediately reboots the system. set variable set variable=value Sets the loader's environment variables. unload Removes all loaded modules. Loader Examples Here are some practical examples of loader usage: single-user mode To simply boot your usual kernel, but in single-user mode: boot -s To unload your usual kernel and modules, and then load just your old (or another) kernel: kernel.old unload load kernel.old You can use kernel.GENERIC to refer to the generic kernel that comes on the install disk, or kernel.old to refer to your previously installed kernel (when you have upgraded or configured your own kernel, for example). Use the following to load your usual modules with another kernel: unload set kernel="kernel.old" boot-conf To load a kernel configuration script (an automated script which does the things you would normally do in the kernel boot-time configurator): load -t userconfig_script /boot/kernel.conf Joseph J. Barbish Contributed by Boot Time Splash Screens The splash screen creates a more visually appealing boot screen compared to the original boot messages. This screen will be displayed until a console login prompt or an X display manager offers a login prompt. There are two basic environments available in &os;. The first is the default legacy virtual console command line environment. After the system finishes booting, a console login prompt is presented. The second environment is the X11 Desktop graphical environment. After X11 and one of the graphical desktop environments, such as GNOME, KDE, or XFce are installed, the X11 desktop can be launched by using the startx command. Some users prefer the X11 graphical login screen over the traditional text based login prompt. Display managers like XDM for &xorg;, gdm for GNOME, and kdm for KDE (and any other from the Ports Collection) basically provide a graphical login screen in place of the console login prompt. After a successful login, they present the user with a graphical desktop. In the command line environment, the splash screen would hide all the boot probe messages and task startup messages before displaying the login prompt. In X11 environment, the users would get a visually clearer system start up experience resembling something closer to what a (µsoft; &windows; or non-unix type system) user would experience. Splash Screen Function The splash screen function only supports 256-color bitmap (.bmp) or ZSoft PCX (.pcx) files. In addition, the splash image files must have a resolution of 320 by 200 pixels or less to work on standard VGA adapters. To use larger images, up to the maximum resolution of 1024 by 768 pixels, activate the VESA support included in &os;. This can be enabled by loading the VESA module during system boot, or adding a VESA kernel configuration option and building a custom kernel (see ). The VESA support gives users the ability to display a splash screen image that fills the whole display screen. While the splash screen is being displayed during the booting process, it can be turned off any time by hitting any key on the keyboard. The splash screen also defaults to being a screen saver outside of X11. After a time period of non-use the screen will change to the splash screen and cycle through steps of changing intensity of the image, from bright to a very dark and over again. This default splash screen (screen saver) behavior could be overridden by adding a saver= line to /etc/rc.conf. Option saver= has several built-in screen savers to choose from, the full list can be found in the &man.splash.4; manual page. The default screen saver is called warp. Note that the saver= option specified in /etc/rc.conf only applies to virtual consoles. It has no effect on X11 display managers. A few boot loader messages, including the boot options menu and a timed wait count down prompt are displayed at boot time, even when the splash screen is enabled. Sample splash screen files can be downloaded from the gallery at . By + url="http://artwork.freebsdgr.org/node/3/">http://artwork.freebsdgr.org. By installing the sysutils/bsd-splash-changer port, splash images can be chosen from a collection randomly at each boot. Enabling the Splash Screen Function The splash screen (.bmp) or (.pcx) file has to be placed on the root partition, for example in the /boot directory. For default boot display resolution (256-color, 320 by 200 pixels, or less), edit /boot/loader.conf, so it contains the following: splash_bmp_load="YES" bitmap_load="YES" bitmap_name="/boot/splash.bmp" For larger video resolutions up to the maximum of 1024 by 768 pixels, edit /boot/loader.conf, so it contains the following: vesa_load="YES" splash_bmp_load="YES" bitmap_load="YES" bitmap_name="/boot/splash.bmp" The above assumes that /boot/splash.bmp is used for splash screen. When a PCX file is desired, use the following statements, plus the vesa_load="YES" line depending on the resolution. splash_pcx_load="YES" bitmap_load="YES" bitmap_name="/boot/splash.pcx" The file name is not restricted to splash as shown in the above example. It can be anything as long as it has type of BMP or PCX, such as splash_640x400.bmp or blue_wave.pcx. Some other interesting loader.conf options: beastie_disable="YES" This will stop the boot options menu from being displayed, but the timed wait count down prompt will still be present. Even with the display of the boot options menu disabled, entering an option selection at the timed wait count down prompt will enact the corresponding boot option. loader_logo="beastie" This will replace the default words &os;, which are displayed to the right of the boot options menu with the colored beastie logo like releases in the past had. For more information, please see the &man.splash.4;, &man.loader.conf.5;, and &man.vga.4; manual pages. Kernel Interaction During Boot kernel boot interaction Once the kernel is loaded by either loader (as usual) or boot2 (bypassing the loader), it examines its boot flags, if any, and adjusts its behavior as necessary. kernel bootflags Kernel Boot Flags Here are the more common boot flags: during kernel initialization, ask for the device to mount as the root file system. boot from CDROM. run UserConfig, the boot-time kernel configurator boot into single-user mode be more verbose during kernel startup There are other boot flags, read &man.boot.8; for more information on them. Tom Rhodes Contributed by device.hints Device Hints This is a FreeBSD 5.0 and later feature which does not exist in earlier versions. During initial system startup, the boot &man.loader.8; will read the &man.device.hints.5; file. This file stores kernel boot information known as variables, sometimes referred to as device hints. These device hints are used by device drivers for device configuration. Device hints may also be specified at the Stage 3 boot loader prompt. Variables can be added using set, removed with unset, and viewed with the show commands. Variables set in the /boot/device.hints file can be overridden here also. Device hints entered at the boot loader are not permanent and will be forgotten on the next reboot. Once the system is booted, the &man.kenv.1; command can be used to dump all of the variables. The syntax for the /boot/device.hints file is one variable per line, using the standard hash # as comment markers. Lines are constructed as follows: hint.driver.unit.keyword="value" The syntax for the Stage 3 boot loader is: set hint.driver.unit.keyword=value driver is the device driver name, unit is the device driver unit number, and keyword is the hint keyword. The keyword may consist of the following options: at: specifies the bus which the device is attached to. port: specifies the start address of the I/O to be used. irq: specifies the interrupt request number to be used. drq: specifies the DMA channel number. maddr: specifies the physical memory address occupied by the device. flags: sets various flag bits for the device. disabled: if set to 1 the device is disabled. Device drivers may accept (or require) more hints not listed here, viewing their manual page is recommended. For more information, consult the &man.device.hints.5;, &man.kenv.1;, &man.loader.conf.5;, and &man.loader.8; manual pages. init Init: Process Control Initialization Once the kernel has finished booting, it passes control to the user process &man.init.8;, which is located at /sbin/init, or the program path specified in the init_path variable in loader. Automatic Reboot Sequence The automatic reboot sequence makes sure that the file systems available on the system are consistent. If they are not, and &man.fsck.8; cannot fix the inconsistencies, &man.init.8; drops the system into single-user mode for the system administrator to take care of the problems directly. Single-User Mode single-user mode console This mode can be reached through the automatic reboot sequence, or by the user booting with the option or setting the boot_single variable in loader. It can also be reached by calling &man.shutdown.8; without the reboot () or halt () options, from multi-user mode. If the system console is set to insecure in /etc/ttys, then the system prompts for the root password before initiating single-user mode. An Insecure Console in <filename>/etc/ttys</filename> # name getty type status comments # # If console is marked "insecure", then init will ask for the root password # when going to single-user mode. console none unknown off insecure An insecure console means that you consider your physical security to the console to be insecure, and want to make sure only someone who knows the root password may use single-user mode, and it does not mean that you want to run your console insecurely. Thus, if you want security, choose insecure, not secure. Multi-User Mode multi-user mode If &man.init.8; finds your file systems to be in order, or once the user has finished in single-user mode, the system enters multi-user mode, in which it starts the resource configuration of the system. rc files Resource Configuration (rc) The resource configuration system reads in configuration defaults from /etc/defaults/rc.conf, and system-specific details from /etc/rc.conf, and then proceeds to mount the system file systems mentioned in /etc/fstab, start up networking services, start up miscellaneous system daemons, and finally runs the startup scripts of locally installed packages. The &man.rc.8; manual page is a good reference to the resource configuration system, as is examining the scripts themselves. Shutdown Sequence shutdown Upon controlled shutdown, via &man.shutdown.8;, &man.init.8; will attempt to run the script /etc/rc.shutdown, and then proceed to send all processes the TERM signal, and subsequently the KILL signal to any that do not terminate timely. To power down a FreeBSD machine on architectures and systems that support power management, simply use the command shutdown -p now to turn the power off immediately. To just reboot a FreeBSD system, just use shutdown -r now. You need to be root or a member of operator group to run &man.shutdown.8;. The &man.halt.8; and &man.reboot.8; commands can also be used, please refer to their manual pages and to &man.shutdown.8;'s one for more information. Power management requires &man.acpi.4; support in the kernel or loaded as module for.