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.

If present, the file /boot.cfg will be used to configure the behaviour of the boot loader including setting the timeout, choosing a console device, altering the banner text and displaying a menu allowing boot commands to be easily chosen. See boot.cfg(5).

The NetBSD/i386 boot loader can boot a kernel using either the native NetBSD boot protocol, or the “multiboot” protocol (which is compatible with some other operating systems). In the native NetBSD boot protocol, options are passed from the boot loader to the kernel via flag bits in the boothowto variable, which is interpreted by the kernel in much the same way as the howto argument passed to the reboot(2) system call. In the multiboot protocol, options are passed from the boot loader to the kernel as strings.

  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] [-1234abcdmqsvxz] 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:

    -1  Sets the machine-dependent flag RB_MD1 in boothowto. In NetBSD/i386, this disables multiprocessor boot; the kernel will boot in uniprocessor mode.

    -2  Sets the machine-dependent flag RB_MD2 in boothowto. In NetBSD/i386, this disables ACPI.

    -3  Sets the machine-dependent flag RB_MD3 in boothowto. In NetBSD/i386, this has no effect.

    -4  Sets the machine-dependent flag RB_MD4 in boothowto. In NetBSD/i386, this has no effect.

    -a  Sets the RB_ASKNAME flag in boothowto. This causes the kernel to prompt for the root file system device, the system crash dump device, and the path to init(8).

    -b  Sets the RB_HALT flag in boothowto. This causes subsequent reboot attempts to halt instead of rebooting.

    -c  Sets the RB_USERCONF flag in boothowto. This causes the kernel to enter the userconf(4) device configuration manager as soon as possible during the boot. userconf(4) allows devices to be enabled or disabled, and allows device locators (such as hardware addresses or bus numbers) to be modified before the kernel attempts to attach the devices.

    -d  Sets the RB_KDB flag in boothowto. Requests the kernel to enter debug mode, in which it waits for a connection from a kernel debugger; see ddb(4).

    -m  Sets the RB_MINIROOT flag in boothowto. Informs the kernel that a mini-root file system is present in memory.

    -q  Sets the AB_QUIET flag in boothowto. Boot the system in quiet mode.

    -s  Sets the RB_SINGLE flag in boothowto. Boot the system in single-user mode.

    -v  Sets the AB_VERBOSE flag in boothowto. Boot the system in verbose mode.

    -x  Sets the AB_DEBUG flag in boothowto. Boot the system with debug messages enabled.

    -z  Sets the AB_SILENT flag in boothowto. Boot the system in silent 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.

load module [arguments]
    Load the specified kernel module, and pass it the specified arguments. If the module name is not an absolute path, /stand/ <arch> / <osversion> /modules/ <module> / <module> .kmod is used. Possible used of the load command include loading a memory disk image before booting a kernel, or loading a Xen DOM0 kernel before booting the Xen hypervisor.

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

multiboot kernel [arguments]
    Boot the specified kernel, using the “multiboot” protocol instead of the native NetBSD boot protocol. The kernel is specified in the same way as with the boot command.

    The multiboot protocol may be used in the following cases:

    NetBSD/Xen kernels
        The Xen DOM0 kernel must be loaded as a module using the load command, and the Xen hypervisor must be booted using the multiboot command. Options for the DOM0 kernel (such as “-s” for single user mode) must be passed as options to the load command. Options for the hypervisor (such as “dom0_mem=256M” to reserve 256 MB of memory for DOM0) must be passed as options to the multiboot command. See boot.cfg(5) for examples of how to boot NetBSD/Xen.

    NetBSD multiboot kernels
        A NetBSD kernel that was built with options MULTIBOOT (see multiboot(8)) may be booted with either the boot or multiboot command, passing the same arguments in either case.

    Non-NetBSD kernels
        A kernel for a non-NetBSD operating system that expects to be booted using the multiboot protocol (such as by the GNU “GRUB” boot loader) may be booted using the multiboot command. See the foreign operating system's documentation for the available arguments.

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 or other media, or over the network.

FILES
/boot
    boot program code loaded by the primary bootstrap
/boot.cfg
    optional configuration file
/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.cfg(5), boot_console(8), dosboot(8), halt(8), installboot(8), mbr(8), multiboot(8), pxeboot(8), reboot(8), shutdown(8), w95boot(8)

BUGS
The kernel file name must be specified before, not after, the boot options. 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).