BOOT(8)               NetBSD/i386 System Manager's Manual              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 boot-
     blocks 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 exam-
     ple above, it will be ``hd0a:netbsd'' which is the file netbsd on parti-
     tion ``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 mes-
     sages 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 installa-
               tion to installation:

               hd      Hard disks as numbered by the BIOS. This includes
                       ST506, IDE, ESDI, RLL disks on a WD100[2367] or looka-
                       like 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 sys-
                    tem crash dump device, and the path to init(8).

               -b   Sets the RB_HALT flag in boothowto.  This causes subse-
                    quent 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 man-
                    ager 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 num-
                    bers) 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 ker-
                    nel 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 specifica-
               tion.

         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 ker-
                       nel (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 installa-
     tion 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 boot-
                              strap
     /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 distinc-
     tion between ``sd'' and ``wd'' devices at the bootloader level.  This is
     less a bug of the bootloader code than a shortcoming of the PC architec-
     ture.  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).

NetBSD 5.0_STABLE              October 30, 2008              NetBSD 5.0_STABLE
