freebsd-dev/sbin/reboot/nextboot.8

.\" Copyright (c) 2002 Gordon Tetlow
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.Dd April 9, 2016
.Dt NEXTBOOT 8
.Os
.Sh NAME
.Nm nextboot
.Nd "specify an alternate kernel and boot flags for the next reboot"
.Sh SYNOPSIS
.Nm
.Op Fl af
.Op Fl e Ar variable=value
.Op Fl k Ar kernel
.Op Fl o Ar options
.Nm
.Fl D
.Sh DESCRIPTION
The
.Nm
utility allows specifying some combination of an alternate kernel, boot flags
and kernel environment for the
next time the machine is booted.
Once the
.Xr loader 8
loads in the new kernel
information, it is deleted so in case the new kernel hangs the machine,
once it is rebooted, the machine will automatically revert to its previous
configuration.
.Pp
The options are as follows:
.Bl -tag -width ".Fl o Ar options"
.It Fl a
This option causes
.Nm
to append to an existing configuration in
.Pa /boot/nextboot.conf .
By default any existing configuration is overwritten.
.It Fl D
Invoking
.Nm
with this
option removes an existing
.Nm
configuration.
.It Fl e Ar variable=value
This option adds the provided variable and value to the kernel environment.
The value is quoted when written to the
.Nm
configuration.
.It Fl f
This
option disables the sanity checking which checks if the kernel really exists
before writing the
.Nm
configuration.
.It Fl k Ar kernel
This option specifies a kernel directory relative to
.Pa /boot
to load the kernel and any modules from.
.It Fl o Ar options
This option
allows the passing of kernel flags for the next boot.
.El
.Sh FILES
.Bl -tag -width ".Pa /boot/nextboot.conf" -compact
.It Pa /boot/nextboot.conf
The configuration file that the
.Nm
configuration is written into.
.El
.Sh EXAMPLES
To boot the
.Pa GENERIC
kernel with the
.Nm
command:
.Pp
.Dl "nextboot -k GENERIC"
.Pp
To enable into single user mode with the normal kernel:
.Pp
.Dl "nextboot -o ""-s"" -k kernel"
.Pp
To remove an existing nextboot configuration:
.Pp
.Dl "nextboot -D"
.Sh SEE ALSO
.Xr boot 8 ,
.Xr loader 8
.Sh HISTORY
The original
.Nm
manual page first appeared in
.Fx 2.2 .
It used a very different interface to achieve similar results.
.Pp
The current incarnation of
.Nm
appeared in
.Fx 5.0 .
.Sh AUTHORS
This manual page was written by
.An Gordon Tetlow Aq Mt gordon@FreeBSD.org .
.Sh BUGS
The
.Nm
code is implemented in the
.Xr loader 8 .
It is not the most thoroughly tested code.
It is also my first attempt to write in Forth.
.Pp
Finally, it does some evil things like writing to the file system before it
has been checked.
If it scrambles your file system, do not blame me.
.Pp
.Xr loader 8
is only able to read ZFS, not write to it.
.Pa nextboot.conf
will NOT be reset in case of a kernel boot failure.