BOOT(8)

NAME
boot - system bootstrapping procedures

DESCRIPTION
Power fail and crash recovery. Normally, the system will reboot itself at power-up or after crashes. An automatic consistency check of the file systems will be performed, and unless this fails, the system will resume multi-user operations.

Cold starts. Most PCs attempt to boot first from hard disk drive 0 (sometimes known as drive C:) and, failing that, from various other mass storage devices. Usually, BIOSes allow you to change this default sequence, and typically also include a CD-ROM drive as a boot device.

Newer PCs boot using UEFI firmware, not legacy BIOS. That process is described in uefi(8).

By default, a three-stage bootstrap is employed, and control is automatically passed from the boot blocks (bootstrap stages one and two) to a separate third-stage bootstrap program, loader(8). This third stage provides more sophisticated control over the booting process than it is possible to achieve in the boot blocks, which are constrained by occupying limited fixed space on a given disk or slice.

However, it is possible to dispense with the third stage altogether, either by specifying a kernel name in the boot block parameter file, /boot.config, or, unless option -n is set, by hitting a key during a brief pause (while one of the characters -, \, |, or / is displayed) before loader(8) is invoked. Booting will also be attempted at stage two, if the third stage cannot be loaded.

The remainder of this subsection deals only with the boot blocks. The loader(8) program is documented separately.

After the boot blocks have been loaded, you should see a prompt similar to the following:

    DragonFly boot
    0:ad(0,a)/boot/loader:

The automatic boot will attempt to load /boot/loader and if that fails /loader from partition ‘a’ of either the floppy or the hard disk. This boot may be aborted by typing any character on the keyboard at the ‘boot:’ prompt. At this time, the following input will be accepted:

?   Give a short listing of the files in the root directory of the default boot device, as a hint about available boot files. (A? may also be specified as the last segment of a path, in which case the listing will be of the relevant subdirectory.)

    bios_drive:interface( unit,part) filename [-aCcDdghmnPprsVv] Specify boot file and flags.

    bios_drive
        The drive number as recognized by the BIOS. 0 for the first drive, 1 for the second drive, etc.

    interface
        The type of controller to boot from. Note that the controller is required to have BIOS support since the BIOS services are used to load the boot file image.

        The supported interfaces are:

        ad  ST506, IDE, ESDI, RLL disks on a WD100[2367] or lookalike controller
        fd  5 ¼" or 3 ½" High density floppies
        da  SCSI disk on any supported SCSI controller

    unit
        The unit number of the drive on the interface being used. 0 for the first drive, 1 for the second drive, etc.

    part
        The partition letter inside the BSD portion of the disk. See disklabel(8). By convention, only partition ‘a’ contains a bootable image. If sliced disks are used (“fdisk partitions”), any slice can be booted from, with the default being the active slice or, otherwise, the first DragonFly slice.

    filename
        The pathname of the file to boot (relative to the root directory on the specified partition). Defaults to /boot/kernel. Symbolic links are not supported (hard links are).

    -aCcDdghmnPprsVv
        Boot flags:

        -a  during kernel initialization, ask for the device to mount as the root file system.
        -C  boot from CDROM.
        -D  Use all available consoles as the system console. Input will be accepted on any console and output will be routed to all of them. This is the default.
        -h  Use the serial console as the system console.
        -V  Use the video console as the system console.
        -m  Mute the system console. None of the console devices will be used for the system console.
        -d  enter the DDB kernel debugger (see ddb(4)) as early as possible in kernel initialization.
        -g  use the GDB remote debugging protocol.
        -n  ignore key press to interrupt boot before loader(8) is invoked.
        -P  probe the keyboard. If no keyboard is found, the -D and -h options are automatically set.
        -p  pause after each attached device during the device probing phase.
        -r  use the statically configured default for the device containing the root file system (see ‘options ROOTDEVNAME’ in the LINT64 kernel configuration file). Normally, the root file system is on the device that the kernel was loaded from.
        -s  boot into single-user mode; if the console is marked as “insecure” (see ttys(5)), the root password must be entered.
        -v  be verbose during device probing (and later).

You may put a BIOS drive number, a controller type, a unit number, a partition, a kernel file name, and any valid option in /boot.config to set defaults. Enter them in one line just as you type at the ‘boot:’ prompt.

FILES
/boot.config
    parameters for the boot blocks (optional)
/boot/boot1
    first stage bootstrap file
/boot/boot2
    second stage bootstrap file
/boot/loader
    third stage bootstrap
/boot/kernel
    default kernel
/boot/kernel.old
    typical non-default kernel (optional)

DIAGNOSTICS
When disk-related errors occur, these are reported by the second-stage bootstrap using the same error codes returned by the BIOS, for example “Disk error 0x1 (lba=0x12345678)”. Here is a partial list of these error codes:

0x1 Invalid argument
0x2 Address mark not found
0x4 Sector not found
0x8 DMA overrun
0x9 DMA attempt across 64K boundary
0xc Invalid media
0x10
    Uncorrectable CRC/ECC error
0x20
    Controller failure
0x40
    Seek failed
0x80
    Timeout

NOTE: On older machines, or otherwise where EDD support (disk packet interface support) is not available, all boot-related files and structures (including the kernel) that need to be accessed during the boot phase must reside on the disk at or below cylinder 1023 (as the BIOS understands the geometry). When a “Disk error 0x1” is reported by the second-stage bootstrap, it generally means that this requirement has not been adhered to.

SEE ALSO
ddb(4), ttys(5), boot0cfg(8), disklabel(8), efibootmgr(8), halt(8), loader(8), reboot(8), shutdown(8), uefi(8)

BUGS
The disklabel(5) format used by this version of BSD is quite different from that of other architectures.

Due to space constraints, the keyboard probe initiated by the -P option is simply a test that the BIOS has detected an “extended” keyboard. If an “XT/AT” keyboard (with no F11 and F12 keys, etc.) is attached, the probe will fail.

Some features are not yet documented.