mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-29 12:03:03 +00:00
116 lines
3.4 KiB
Groff
116 lines
3.4 KiB
Groff
.\" $FreeBSD$
|
|
.Dd July 9, 1996
|
|
.Dt NEXTBOOT 8
|
|
.Os
|
|
.Sh NAME
|
|
.Nm nextboot
|
|
.Nd install a default bootstring block on the boot disk
|
|
.Sh SYNOPSIS
|
|
.Nm
|
|
.Op Fl b
|
|
.Ar filename bootstring
|
|
.Ar
|
|
.Nm
|
|
.Op Fl ed
|
|
.Ar filename
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fx
|
|
program
|
|
.Nm
|
|
controls the actions of the boot blocks at the time of the next boot.
|
|
If compiled with the correct option,
|
|
the boot blocks will check the nameblock for a magic number and a
|
|
default name to use for booting.
|
|
If compiled to do so they will also
|
|
delete the name from the block, ensuring that if the boot should fail,
|
|
then it will not be tried again.
|
|
It is the job of
|
|
.Pa /etc/rc
|
|
to use
|
|
.Nm
|
|
to re-install the string if that boot is found to have succeeded.
|
|
This allows a one-time only boot string to be used for such applications
|
|
as remote debugging, and installation of new, untrusted kernels.
|
|
The nameblock is defined at compile time to be the second physical block
|
|
on the disk.
|
|
.Pp
|
|
The following options are available:
|
|
.Bl -tag -width indent
|
|
.It Fl b
|
|
Is used for bootstrapping (initially configuring) the nameblock.
|
|
Without
|
|
this,
|
|
.Nm
|
|
will refuse to write to a block that does not already contain the magic
|
|
number.
|
|
.It Fl d
|
|
Disable (temporarily) an existing name block by changing a bit
|
|
in the magic number.
|
|
.It Fl e
|
|
Restore the good magic number on a block disabled by
|
|
.Fl d .
|
|
.El
|
|
.Pp
|
|
The
|
|
.Fl e
|
|
and
|
|
.Fl d
|
|
flags are mutually exclusive.
|
|
.Sh DESCRIPTION
|
|
.Nm Nextboot
|
|
first checks that the disk has an fdisk table and checks that none of the
|
|
partitions defined in that table include the nameblock.
|
|
If the name block is
|
|
shown to be unused, it will install the bootstrings given as arguments,
|
|
one after the other, each preceded by a small magic number, and NULL
|
|
terminated.
|
|
The end of the list of strings is delimited by a sequence of
|
|
0xff bytes.
|
|
If the boot blocks are compiled to write back the nameblock
|
|
after each boot, it will zero out the supplied names as it uses them,
|
|
one per boot,
|
|
until it reaches the 0xff, at which time it will revert to the compiled in
|
|
boot string.
|
|
At this time the nameblock will contain only zeroed out names.
|
|
.Pp
|
|
An example of usage might be:
|
|
.Bd -literal
|
|
nextboot -b /dev/rwd0 1:sd(0,a)/kernel.experimental wd(0,a)/kernel.old
|
|
.Ed
|
|
.Pp
|
|
Which would instruct the boot blocks at the next boot,
|
|
to try boot the experimental kernel off the SCSI disk.
|
|
If for any reason this failed, the next boot attempt would
|
|
boot the kernel
|
|
.Pa /kernel.old
|
|
off the IDE drive. (Assuming the write-back option were enabled) If this
|
|
in turn failed.
|
|
The compiled in default would be used.
|
|
.Pp
|
|
If the write-back feature is disabled, the nextboot program is a convenient way
|
|
to change the default boot string.
|
|
Note, that should the file specified in
|
|
the nameblock be non-existent, then the name compiled into the boot blocks
|
|
will be used for the boot rather than the next name in the nameblock.
|
|
The
|
|
nameblock is only consulted
|
|
.Em once
|
|
per boot.
|
|
.Sh SEE ALSO
|
|
.Xr boot 8 ,
|
|
.Xr disklabel 8 ,
|
|
.Xr fdisk 8
|
|
.Sh BUGS
|
|
This program works only in conjunction with the legacy boot code.
|
|
.Pp
|
|
The entire program should be made more user-friendly.
|
|
The option of whether to write back or not should be stored on the
|
|
disk and not a compile time option.
|
|
I want to rethink this at some
|
|
later stage to make it co-exist with disks that do not have
|
|
a fdisk partitioning table (i.e. purely disklabel'd systems).
|
|
.Pp
|
|
Whether to write back or not should be specified at run-time in the nameblock
|
|
so that the boot blocks need not be altered to get this feature.
|