NEXTBOOT(8) FreeBSD System Manager's Manual NEXTBOOT(8)


nextbootspecify an alternate kernel and boot flags for the next reboot


nextboot [ -e variable=value][ -f][ -k kernel][ -o options]

nextboot -D


The nextboot utility allows specifying some combination of an alternate kernel, boot flags and kernel environment for the next time the machine is booted. Once the 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.

The options are as follows:

Invoking nextboot with this option removes an existing nextboot configuration.
-e variable=value
This option adds the provided variable and value to the kernel environment. The value is quoted when written to the nextboot configuration.
This option disables the sanity checking which checks if the kernel really exists before writing the nextboot configuration.
-k kernel
This option specifies a kernel directory relative to /boot to load the kernel and any modules from.
-o options
This option allows the passing of kernel flags for the next boot.


The configuration file that the nextboot configuration is written into.


To boot the GENERIC kernel with the nextboot command:

nextboot -k GENERIC

To enable into single user mode with the normal kernel:

nextboot -o "-s" -k kernel

To remove an existing nextboot configuration:

nextboot -D


boot(8), loader(8)


The original nextboot manual page first appeared in FreeBSD 2.2. It used a very different interface to achieve similar results.

The current incarnation of nextboot appeared in FreeBSD 5.0.


This manual page was written by Gordon Tetlow <gordon@FreeBSD.org>.


The nextboot code is implemented in the loader(8). It is not the most thoroughly tested code. It is also my first attempt to write in Forth.

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.

January 31, 2012 FreeBSD