BOOT(8)

NAME
boot - system bootstrapping procedures

DESCRIPTION
IA-32 computers ( the IBM PC and its clones) that can run NetBSD/i386 can use any of the following boot procedures, depending on what the hardware and BIOS support:

boot
    bootstrap NetBSD from the system BIOS

dosboot(8)
    bootstrap NetBSD from MS-DOS

w95boot(8)
    bootstrap NetBSD from Windows 95

pxeboot(8)
    network bootstrap NetBSD from a TCP/IP LAN with DHCP, TFTP, and NFS.

  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
The 386 PC AT clones attempt to boot the floppy disk drive A (otherwise known as drive 0) first, and failing that, attempt to boot the hard disk C (otherwise known as hard disk controller 1, drive 0). The NetBSD bootblocks are loaded and started either by the BIOS, or by a boot selector program (such as OS-BS, BOOTEASY, the OS/2 Boot Menu or NetBSD's boot-selecting master boot record - see mbr(8)).

  Normal Operation
Once running, a banner similar to the following will appear:

     NetBSD BIOS Boot, revision 3.0
     (user@buildhost, builddate)
     Memory: 637/15360 k
    Press return to boot now, any other key for boot menu
    booting hd0a:netbsd - starting in 5

After a countdown, the system image listed will be loaded. In the example above, it will be “hd0a:netbsd” which is the file netbsd on partition “a” of the NetBSD MBR partition of the first hard disk known to the BIOS ( which is an IDE or similar device - see the BUGS section).

Pressing a key within the time limit, or before the boot program starts, will enter interactive mode. When using a short or 0 timeout, it is often useful to interrupt the boot by holding down a shift key, as some BIOSes and BIOS extensions will drain the keystroke buffer at various points during POST.

  Diagnostic Output
If the first stage boot fails to load the boot, it will print a terse message indicating the reason for the failure. The possible error messages and their cause are listed in mbr(8).

If the first stage boot succeeds, the banner will be shown and the error messages should be self-explanatory.

  Interactive mode
In interactive mode, the boot loader will present a prompt, allowing input of these commands:

boot
    [device:] [filename] [-acdqsv] The default device will be set to the disk that the boot loader was loaded from. To boot from an alternate disk, the full name of the device should be given at the prompt. device is of the form xd [N[x]] where xd is the device from which to boot, N is the unit number, and x is the partition letter.

    The following list of supported devices may vary from installation to installation:

    hd  Hard disks as numbered by the BIOS. This includes ST506, IDE, ESDI, RLL disks on a WD100[2367] or lookalike controller(s), and SCSI disks on SCSI controllers recognized by the BIOS.
    fd  Floppy drives as numbered by the BIOS.

    The default filename is netbsd; if the boot loader fails to successfully open that image, it then tries netbsd.gz (expected to be a kernel image compressed by gzip), followed by netbsd.old, netbsd.old.gz, onetbsd, and finally onetbsd.gz. Alternate system images can be loaded by just specifying the name of the image.

    Options are:

    -a  Prompt for the root file system device, the system crash dump device, and the path to init(8).

    -c  Bring the system up into the device configuration manager. From here the device locators can be tuned to the hardware; see userconf(4).

    -d  Bring the system up in debug mode. Here it waits for a kernel debugger connect; see ddb(4).

    -q  Boot the system in quiet mode.

    -s  Bring the system up in single-user mode.

    -v  Boot the system in verbose mode.

consdev dev
    Immediately switch the console to the specified device dev and reprint the banner. dev must be one of pc, com0, com1, com2, com3, com0kbd, com1kbd, com2kbd, com3kbd, or auto. See Console Selection Policy in boot_console(8).

dev [device]
    Set the default drive and partition for subsequent filesystem operations. Without an argument, print the current setting. device is of the form specified in boot.

help
    Print an overview about commands and arguments.

ls [path]
    Print a directory listing of path, containing inode number, filename and file type. path can contain a device specification.

quit
    Reboot the system.

In an emergency, the bootstrap methods described in the NetBSD installation notes for the i386 architecture can be used to boot from floppy.

FILES
/boot
    boot program code loaded by the primary bootstrap
/netbsd
    system code
/netbsd.gz
    gzip-compressed system code
/usr/mdec/boot
    master copy of the boot program (copy to /boot)
/usr/mdec/bootxx_fstype
    primary bootstrap for filesystem type fstype, copied to the start of the netbsd partition by installboot(8).

SEE ALSO
ddb(4), userconf(4), boot_console(8), dosboot(8), halt(8), installboot(8), mbr(8), pxeboot(8), reboot(8), shutdown(8), w95boot(8)

BUGS
This manual page documents the boot interface, which is used by ports other than NetBSD/i386.

Any filename specified after the boot options, e.g.:

    boot -d netbsd.test

is ignored, and the default kernel is booted.

Hard disks are always accessed by BIOS functions. Unit numbers are BIOS device numbers which might differ from numbering in the NetBSD kernel or physical parameters ( e.g., SCSI slave numbers). There isn't any distinction between “sd” and “wd” devices at the bootloader level. This is less a bug of the bootloader code than a shortcoming of the PC architecture. The default disk device's name printed in the starting message is derived from the “type” field of the NetBSD disklabel (if it is a hard disk).