The program grub-set-default sets the default boot entry for GRUB. This automatically creates a file named default under your GRUB directory (i.e. /boot/grub), if it is not present. This file is used to determine the default boot entry when GRUB boots up your system when you use default saved' in your configuration file (see default), and to save next default boot entry when you use savedefault' in a boot entry (see savedefault).
Options
grub-set-default accepts the following options:
--help
Print a summary of the command-line options and exit.
--version
Print the version information and exit.
--root-directory=dir
Use the directory dir instead of the root directory (i.e. /) to define the location of the default file. This is useful when you mount a disk which is used for another system.
You must specify a single argument to grub-set-default. This argument is normally the number of a default boot entry. For example, if you have this configuration file:
default saved
timeout 10
title GNU/Hurd
root (hd0,0)
...
title GNU/Linux
root (hd0,1)
...
and if you want to set the next default boot entry to GNU/Linux, you may execute this command:
grub-set-default 1
Because the entry for GNU/Linux is `1'. Note that entries are counted from zero. So, if you want to specify GNU/Hurd here, then you should specify `0'.
This feature is very useful if you want to test a new kernel or to make your system quite robust. See Making your system robust, for more hints about how to set up a robust system.