xref: /netbsd-src/share/man/man5/boot.cfg.5 (revision c10cd063e1c81200cab209deb115c478262fd172)

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.Dd November 24, 2020
.Dt BOOT.CFG 5
.Os
.Sh NAME
.Nm boot.cfg
.Nd configuration file for /boot
.Sh DESCRIPTION
The file
.Pa /boot.cfg
is used to alter the behaviour of the standard boot loader described in
.Xr boot 8 .
Configuration changes include setting the timeout, choosing a console device,
altering the banner text and displaying a menu allowing boot commands to be
easily chosen.
If a
.Nm
file is not present, the system will boot as normal.
.Ss FILE FORMAT
The format of the file is a series of lines containing keyword/value pairs
separated by an equals sign
.Pq Sq = .
There should be no whitespace surrounding the equals sign.
Lines beginning with a hash
.Pq Sq #
are comments and will be ignored.
.Pp
The
.Dq Ic banner ,
.Dq Ic load ,
.Dq Ic menu ,
and
.Dq Ic userconf
keywords can be present multiple times in the file to define additional
items.
See the description for each keyword for guidance and limitations on
using multiple entries.
.Bl -tag -width timeout
.It Sy banner
The text from banner lines is displayed instead of the standard welcome text
by the boot loader.
Up to 12 lines can be defined.
No special character sequences are recognised, so to specify a blank line, a
banner line with no value should be given.
.It Sy clear
If nonzero, clear the screen before printing the banner.
If zero, do not clear the screen (the default).
.It Sy consdev
Changes the console device to that specified in the value.
Valid values are any of those that could be specified at the normal boot
prompt with the consdev command.
.It Sy default
Used to specify the default menu item  which will be chosen in the case of
Return being pressed or the timeout timer reaching zero.
The value is the number of the menu item as displayed.
As described above, the menu items are counted from 1 in the order listed in
.Nm .
If not specified, the default value will be option 1, i.e. the first item.
.It Sy format
Changes how the menu options are displayed.
Should be set to one of
.Sq a
for automatic,
.Sq l
for letters and
.Sq n
for numbers.
If set to automatic (the default), menu options will be displayed numerically
unless there are more than 9 options and the timeout is greater than zero.
If there are more than 9 options with a timeout greater than zero and
the format is set to number, only the first 9 options will be available.
.It Sy load
Used to load kernel modules, which will be passed on to the kernel for
initialization during early boot.
The argument is either the complete path and file name of the module to be
loaded, or a symbolic module name.
When the argument is not an absolute path, the boot loader will first
attempt to load
.Pa /stand/<machine>/<kernel_version>/modules/<name>/<name>.kmod .
If that file does not exist, it will then attempt to load
.Pa /<name> .
May be used as many times as needed.
.It Sy menu
Used to define a menu item to be displayed to the end-user at boot time
which allows a series of boot commands to be run without further typing.
The value consists of the required menu text, followed by a colon
.Pq Sq \&:
and then the desired command(s).
Multiple commands can be specified separated by a semi-colon.
If the specified menu text is empty
(the colon appears immediately after the equals sign),
then the displayed menu text is the same as the command.
For example:
.Bd -literal
menu=Boot normally:boot
menu=Boot single-user:boot -s
menu=Boot with module foo:load /foo.kmod;boot
menu=Boot with serial console:consdev com0;boot
menu=:boot hd1a:netbsd -as
.Ed
.Pp
Each menu item will be prefixed by an ascending number when displayed,
i.e. the order in the
.Nm
file is important.
.Pp
Each command is executed just as though the user had typed it in
and so can be any valid command that would be accepted at the
normal boot prompt.
In addition,
.Dq Ic prompt
can be used to drop to the normal boot prompt.
.It Sy rndseed
Takes the path to a random-seed file as written by the
.Fl S
flag to
.Xr rndctl 8
as an argument.
This file is used to seed the kernel entropy pool
.Xr rnd 9
very early in kernel startup, so that high quality randomness is
available to all kernel modules.
This argument should be supplied
before any
.Dq Ic load
commands that may load executable modules.
.It Sy timeout
If the value is greater than zero, this specifies the time in seconds
that the boot loader will wait for the end-user to choose a menu item.
During the countdown period, they may press Return to choose the default
option or press a number key corresponding to a menu option.
If any other key is pressed, the countdown will stop and the user will be
prompted to choose a menu option with no further time limit.
If the timeout value is set to zero, the default option will be booted
immediately.
If the timeout value is negative or is not a number, there will be no
time limit for the user to choose an option.
.It Sy userconf
Passes a
.Xr userconf 4
command to the kernel at boot time.
May be used as many times as needed.
.El
.Sh EXAMPLES
Here is an example
.Nm
file:
.Bd -literal -offset indent
banner=Welcome to NetBSD
banner==================
banner=
banner=Please choose an option from the following menu:
menu=Boot normally:boot
menu=Boot single-user:boot -s
menu=Boot from second disk:boot hd1a:
menu=Boot with module foo:load /foo.kmod;boot
menu=Boot with modules foo and bar:load /foo.kmod;load /bar.kmod;boot
menu=Boot Xen with 256MB for dom0:load /netbsd-XEN3_DOM0 console=pc;multiboot /usr/pkg/xen3-kernel/xen.gz dom0_mem=256M
menu=Boot Xen with 256MB for dom0 (serial):load /netbsd-XEN3_DOM0 console=com0;multiboot /usr/pkg/xen3-kernel/xen.gz dom0_mem=256M console=com1 com1=115200,8n1
menu=Boot Xen with dom0 in single-user mode:load /netbsd-XEN3_DOM0 -s;multiboot /usr/pkg/xen3-kernel/xen.gz dom0_mem=256M
menu=Go to command line (advanced users only):prompt
clear=1
timeout=-1
default=1
# Disable Direct Rendering Manager (DRM) drivers
userconf=disable i915drmkms*
userconf=disable nouveau*
userconf=disable radeon*
# Always load ramdisk module
load=/miniroot.kmod
.Ed
.Pp
N.B. Xen counts serial ports from com1 upwards, but
.Nx
counts from com0, so the appropriate device name must be used.
Please see the Xen with serial console example above.
.Pp
This will clear the screen and display:
.Bd -literal -offset indent
Welcome to NetBSD
=================

Please choose an option from the following menu:

      1. Boot normally
      2. Boot single-user
      3. Boot from second disk
      4. Boot with module foo
      5. Boot with modules foo and bar
      6. Boot Xen with 256 MB for dom0
      7. Boot Xen with 256 MB for dom0 (serial)
      8. Boot Xen with dom0 in single-user mode
      9. Go to command line (advanced users only)

Option [1]:
.Ed
.Pp
It will then wait for the user to type 1, 2, 3, 4, 5, 6, 7, 8 or 9 followed by
Return.
Pressing Return by itself will run option 1.
There will be no timeout.
.Sh SEE ALSO
.Xr boot 8 ,
.Xr boothowto 9
.Sh HISTORY
The
.Nm
file appeared in
.Nx 5.0 .
.Sh AUTHORS
The
.Nm
extensions to
.Xr boot 8
were written by
.An Stephen Borrill
.Aq sborrill@NetBSD.org .
.Sh BUGS
Support for
.Nm
is currently for
.Nx Ns /i386
and
.Nx Ns /amd64
only.
It is hoped that its use will be extended to other appropriate ports that
use the
.Xr boot 8
interface.