Recovering a Broken System
Sometimes, things go wrong, and the system you've carefully installed is no
longer bootable. Perhaps the boot loader configuration broke while trying
out a change, or perhaps a new kernel you installed won't boot, or perhaps
cosmic rays hit your disk and flipped a bit in
/sbin/init. Regardless of the cause, you'll need to
have a system to work from while you fix it, and rescue mode can be useful
for this.
To access rescue mode, type rescue at the
boot: prompt, or boot with the
rescue/enable=true boot parameter. You'll be shown
the first few screens of the installer, with a note in the corner of the
display to indicate that this is rescue mode, not a full installation. Don't
worry, your system is not about to be overwritten! Rescue mode simply takes
advantage of the hardware detection facilities available in the installer to
ensure that your disks, network devices, and so on are available to you
while repairing your system.
Instead of the partitioning tool, you should now be presented with a list of
the partitions on your system, and asked to select one of them. Normally,
you should select the partition containing the root file system that you
need to repair. You may select partitions on RAID and LVM devices as well as
those created directly on disks.
If possible, the installer will now present you with a shell prompt in the
file system you selected, which you can use to perform any necessary
repairs.
For example, if you need to reinstall the GRUB boot loader into the master
boot record of the first hard disk, you could enter the command
grub-install '(hd0)' to do so.
If the installer cannot run a usable shell in the root file system you
selected, perhaps because the file system is corrupt, then it will issue a
warning and offer to give you a shell in the installer environment instead.
You may not have as many tools available in this environment, but they will
often be enough to repair your system anyway. The root file system you
selected will be mounted on the /target directory.
In either case, after you exit the shell, the system will reboot.
Finally, note that repairing broken systems can be difficult, and this
manual does not attempt to go into all the things that might have gone wrong
or how to fix them. If you have problems, consult an expert.
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