xref: /freebsd/sbin/reboot/boot_i386.8 (revision 51e16cb8fc536913f490ac6bc9c17e92ebd0411b)

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.Dd July 11, 2020
.Dt BOOT 8 i386
.Os
.Sh NAME
.Nm boot
.Nd system bootstrapping procedures
.Sh DESCRIPTION
.Sy 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.
.Pp
.Sy Cold starts .
Most i386 PCs attempt to boot first from floppy disk drive 0 (sometimes
known as drive A:) and, failing that, from hard disk drive 0 (sometimes
known as drive C:, or as drive 0x80 to the BIOS).
Some BIOSes allow
you to change this default sequence, and may also include a CD-ROM
drive as a boot device.
.Pp
Some newer PCs boot using UEFI firmware, not BIOS.
That process is described
in
.Xr uefi 8 .
.Pp
A three-stage bootstrap is employed.
Control is passed from the boot blocks (bootstrap stages one and two) to a
third-stage bootstrap program,
.Xr 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.
.Pp
The remainder of this subsection deals only with the boot blocks.
The
.Xr loader 8
program is documented separately.
.Pp
After the boot blocks have been loaded,
you should see a prompt similar to the following:
.Bd -literal
>> FreeBSD/x86 BOOT
Default: 0:ad(0,a)/boot/loader
boot:
.Ed
.Pp
The automatic boot will attempt to load
.Pa /boot/loader
from partition
.Ql a
of either the floppy or the hard disk.
This boot may be aborted by typing any character on the keyboard
at the
.Ql boot\&:
prompt.
At this time, the following input will be accepted:
.Bl -tag -width indent
.It Ic \&?
Give a short listing of the files in the root directory of the default
boot device, as a hint about available boot files.
(A
.Ic ?\&
may also be specified as the last segment of a path, in which case
the listing will be of the relevant subdirectory.)
.It Xo
.Sm off
.Ar bios_drive : interface ( unit , Oo Ar slice , Oc Ar part )
.Ar filename
.Sm on
.Op Fl aCcDdghmnPprsv
.Op Fl S Ns Ar speed
.Xc
Specify boot file and flags.
.Bl -tag -width indent
.It Ar bios_drive
The drive number as recognized by the BIOS.
0 for the first drive, 1 for the second drive, etc.
.It Ar 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.
.Pp
The supported interfaces are:
.Pp
.Bl -tag -width "adXX" -compact
.It ad
ST506, IDE, ESDI, RLL disks on a WD100[2367] or lookalike
controller
.It fd
5 1/4" or 3 1/2" High density floppies
.It da
SCSI disk on any supported SCSI controller
.\".It cd
.\"boot from CDROM
.El
.It Ar unit
The unit number of the drive on the interface being used.
0 for the first drive, 1 for the second drive, etc.
.It Oo Ar slice , Oc Ns Ar part
The partition letter inside the
.Bx
portion of the disk.
See
.Xr bsdlabel 8 .
By convention, only partition
.Ql a
contains a bootable image.
If sliced disks are used
.Pq Dq fdisk partitions ,
any
.Ar slice
(1 for the first slice, 2 for the second slice, etc.\&)
can be booted from, with the default (if not specified) being the active slice
or, otherwise, the first
.Fx
slice.
If
.Ar slice
is specified as 0, the first
.Fx
slice (also known as
.Dq compatibility
slice) is booted from.
.It Ar filename
The pathname of the file to boot (relative to the root directory
on the specified partition).
Defaults to
.Pa /boot/kernel/kernel .
Symbolic links are not supported (hard links are).
.It Xo Op Fl aCcDdghmnPpqrsv
.Op Fl S Ns Ar speed
.Xc
Boot flags:
.Pp
.Bl -tag -width "-CXX" -compact
.It Fl a
during kernel initialization,
ask for the device to mount as the root file system.
.It Fl C
try to mount root file system from a CD-ROM.
.It Fl c
this flag is currently a no-op.
.It Fl D
boot with the dual console configuration.
In the single
configuration, the console will be either the internal display
or the serial port, depending on the state of the
.Fl h
option below.
In the dual console configuration,
both the internal display and the serial port will become the console
at the same time, regardless of the state of the
.Fl h
option.
.It Fl d
enter the DDB kernel debugger
(see
.Xr ddb 4 )
as early as possible in kernel initialization.
.It Fl g
use the GDB remote debugging protocol.
.It Fl h
force the serial console.
For instance, if you boot from the internal console,
you can use the
.Fl h
option to force the kernel to use the serial port as its
console device.
.It Fl m
mute the console to suppress all kernel console input and output during the
boot.
.It Fl n
ignore key press to interrupt boot before
.Xr loader 8
is invoked.
.It Fl P
probe the keyboard.
If no keyboard is found, the
.Fl D
and
.Fl h
options are automatically set.
.It Fl p
pause after each attached device during the device probing phase.
.It Fl q
be quiet,
do not write anything to the console unless automatic boot fails or
is disabled.
This option only affects second-stage bootstrap,
to prevent next stages from writing to the console use in
combination with the
.Fl m
option.
.It Fl r
use the statically configured default for the device containing the
root file system
(see
.Xr config 8 ) .
Normally, the root file system is on the device
that the kernel was loaded from.
.It Fl s
boot into single-user mode; if the console is marked as
.Dq insecure
(see
.Xr ttys 5 ) ,
the root password must be entered.
.It Fl S Ns Ar speed
set the speed of the serial console to
.Ar speed .
The default is 115200 unless it has been overridden by setting
.Va BOOT_COMCONSOLE_SPEED
in
.Xr make.conf 5
and recompiling and reinstalling the boot blocks.
.It Fl v
be verbose during device probing (and later).
.El
.El
.El
.Pp
Use the
.Pa /boot.config
file to set the default configuration options for the boot block code.
See
.Xr boot.config 5
for more information about the
.Pa /boot.config
file.
.Sh FILES
.Bl -tag -width /boot/loader -compact
.It Pa /boot.config
parameters for the boot blocks (optional)
.It Pa /boot/boot1
first stage bootstrap file
.It Pa /boot/boot2
second stage bootstrap file
.It Pa /boot/loader
third stage bootstrap
.It Pa /boot/kernel/kernel
default kernel
.It Pa /boot/kernel.old/kernel
typical non-default kernel (optional)
.El
.Sh 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
.Dq Disk error 0x1 (lba=0x12345678) .
Here is a partial list of these error codes:
.Pp
.Bl -tag -width "0x80" -compact
.It 0x1
Invalid argument
.It 0x2
Address mark not found
.It 0x4
Sector not found
.It 0x8
DMA overrun
.It 0x9
DMA attempt across 64K boundary
.It 0xc
Invalid media
.It 0x10
Uncorrectable CRC/ECC error
.It 0x20
Controller failure
.It 0x40
Seek failed
.It 0x80
Timeout
.El
.Pp
.Sy "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
.Dq Disk error 0x1
is reported by the second-stage bootstrap, it generally means that this
requirement has not been adhered to.
.Sh SEE ALSO
.Xr ddb 4 ,
.Xr boot.config 5 ,
.Xr make.conf 5 ,
.Xr mount.conf 5 ,
.Xr ttys 5 ,
.Xr boot0cfg 8 ,
.Xr btxld 8 ,
.Xr config 8 ,
.Xr efibootmgr 8 ,
.Xr efivar 8 ,
.Xr gpart 8 ,
.Xr gptboot 8 ,
.Xr gptzfsboot 8 ,
.Xr halt 8 ,
.Xr loader 8 ,
.Xr nextboot 8 ,
.Xr reboot 8 ,
.Xr shutdown 8 ,
.Xr uefi 8 ,
.Xr zfsbootcfg 8
.Sh BUGS
The bsdlabel format used by this version of
.Bx
is quite
different from that of other architectures.
.Pp
Due to space constraints, the keyboard probe initiated by the
.Fl P
option is simply a test that the BIOS has detected an
.Dq extended
keyboard.
If an
.Dq XT/AT
keyboard (with no F11 and F12 keys, etc.) is attached, the probe will
fail.