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Very often less experienced Linux users counter system
problems with the troubleshooting technique they've learned on other operating
systems: they reinstall the whole operating system.
This of course does not only cost quite a massive account of time, it also
prevents them to feel really secure with the system, all the more since these
users usually do not keep backups.
There are very few compelling reasons to ever
reinstall Linux, like massive file system corruption or a hard drive failure.
You can repair everything else either from within the system or from outside
(via a network connection or a boot disk/CD). In contrast to other operating
systems all configuration files are in plain text and can be edited with
the most simple text editor. Furthermore you can reinstall, upgrade or downgrade
every part of the system, since Linux only needs a minimal set of files to
provide the basic functions of an operating system.
Being able to repair a system is what makes you an administrator,
it is arguably the most important step from being controlled by your system
to take control of it.
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There is nothing wrong with using graphical tools to
configure and administer your system. These tools often make it easier to
handle complex tasks and to get things working.
In a case of emergency, however, you will most likely not be able to access
them. That's why Linux administration requires at least some rudimentary knowledge
of using the 'traditional' command line Unix tools.
vi
The most basic rescue tool, like it or not, is the text
editor. In most cases, and on the Mandrake Linux rescue system, that's the
'vi' editor, a minimal version of 'vim'.
You open a file with 'vi' thus:
vi file
If the file isn't in the current directory, you have
to put the path to that file in front of the file name:
vi /some/path/file
'vi' now displays the file. To edit the displayed file,
press the<i> key. You can then move around with cursor keys
insert and delete text with the usual keys.
To save an edited file, press the <ESC> key and then press
<Z> twice. Notice that 'vi' makes a difference
between capital and small letters, so make sure you press a capital
'Z' twice here.
To quit editing a file without saving the changes you made to it, press these
keys one after the other <ESC> <:> <q> <!> <ENTER>.
Of course there's much more to 'vi' and 'vim'. Even
if you do not adopt it as your favorite editor, you should get comfortable
with using its basic functions, since this training will be of use
to you some day. You might want to read Vikram Vaswani's Vi
101 for an entertaining introduction into the Vi editor and print out
Krissy J's Vi short command
reference.
Notice:
-
The 'vi' command does not work on Mandrake Linux
when the 'vim-enhanced' package is installed and you are working on a partition
which only contains the root directory with no other partitions mounted.
Use vim-minimal instead or run
# update-alternatives --config vi
to set the name of the executed binary back to '/bin/vim-minimal'.
mount
Although the current Mandrake Linux rescue system mounts
your Linux partition automatically when started, there might be circumstances
when you have to mount or unmount partitions or external media by hand, e.g.
when your are using an older release or when your machine doesn't have a
bootable CD drive, if you need to do a file system check or need access to
external media.
Mounting is discussed in depth in another article in this section, but here are the
basics.
In order to mount a medium, you need to know its device
file name. If it is a partition on a hard disk, it's pretty easy to find
out:
fdisk -l /dev/device
device stands for the device file name of
the hard disk. In most case, it will be 'hda', the first IDE hard disk on
the first IDE channel:
fdisk -l /dev/hda
This will list all partitions on that disk along with
their device names. The second hard disk ('slave' on the first IDE channel)
would be 'hdb', the first disk on the second channel 'hdc' etc. Notice that
if you've got your hard disk connected to an UDMA-100 controller (on-board
or card), the name of the first hard disk is 'hde'.
For more device file names read the article linked to above.
To mount a medium, you type
mount /dev/device mount_directory
mount_directory can be any existing directory
on the current medium, preferably an empty one. To unmount a medium, a simple
umount mount_directory
suffices.
fsck
'fsck' a utility for performing file system checks and
repairs. You start a file system check this way:
fsck -t file_system device_file
file_system has to be substituted by the
file system on the partition you want to check. In contrast to 'mount', 'fsck'
can't figure out the file system type on its own.
Instead of using the '-t file_system' option, you can also call
the file system specific variants of 'fsck' directly: 'fsck.ext2', 'fsck.jfs',
'fsck.xfs' and 'reiserfsck'. This is actually the preferred way, since it
eliminates the chance of getting options to 'fsck' and 'fsck.fs'
mixed up.
Thus, to check the second primary partition on the first IDE hard drive which
has the file system 'ext2':
fsck.ext2 /dev/hdb
Notice:
- 'fsck' should only be run on unmounted
file systems.
- 'fsck.ext2' will also work on 'ext3' file systems.
- By default 'fsck.ext2' will not check a file system
which has been cleanly unmounted. To force it to do a check, use the '-f'
option.
- The man page to 'fsck.ext2' is man e2fsck.
- 'fsck.xfs' doesn't do anything. To repair an XFS,
use 'xfs_repair'.
- Please be aware that the man pages to these tools
might not be available in case of an emergency.
By default, a file system check will be run interactively,
that is every time the checker encounters an error, it asks you if to fix
it. If you find this annoying, you can turn off these questions with the
'-a' option in all checkers (although 'fsck.ext2' prefers '-p').
Others
Make yourself familiar with these commands: 'mv', 'cp',
'rm', 'ls', 'cd', 'grep' and 'less'. This doesn't mean you should learn their
man pages by heart, but you should know what they do and how to handle them.
Youwill need them some day, believe me ;-).
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Mandrake Linux comes with a rescue system on the first
CD (list of contents), introduced
in release 7.1. In case your CD-R drive isn't bootable, boot from a boot
floppy (images are in the '/images' directory of the first CD).
To start this rescue system, press the <F1> key and type
rescue on the prompt at the bottom of the screen.
Press the<ENTER> key. The rescue system will now boot from
the CD, loading itself into system memory (at least 32 MB RAM needed).
In Mandrake Linux 8.2 and later, you will be presented
with a text menu listing the most common tasks you'd use the rescue system
for:
-
Re-install Boot Loader. This is useful if you've
recently (re-)installed another operating system which erased the boot loader
installed by Mandrake Linux. This operation will revert this so that you
can start every configured operating system from the boot loader menu again.
-
Restore Windows Boot Loader. Upon installing the
boot loader, Mandrake Linux makes a backup copy of the previous boot code.
This operation writes this backup copy back to the boot sector, thus erasing
the boot loader installed by Mandrake Linux.
-
Mount your partitions under /mnt. Use this if you
want to access your Linux partitions on the hard drive from the console.
The rescue system will make an educated guess which partitions to mount to
what directories.
-
Go to console. Starts a console without mounting
any partitions. Might be useful if the rescue system can't figure out your
partition scheme or if you have several Linux installations.
-
Reboot. Well ...
-
Doc. Read some good advice on using the rescue system.
Upon booting, the rescue system will automatically try
to mount any available Linux hard disk partitions, which can then be accessed
via the '/mnt' directory.
The rescue needs only system memory to work, which means you can remove the
CD after boot (e.g. to use the drive to mount another CD).
The software contained in the rescue system allows you
to
- delete, move, copy, (un)archive, (de)compress and
create files, directories and symlinks to files;
- display, edit and create text files (including hex
files);
- check and repair every file system available with
Mandrake Linux;
- create, delete, resize (ext2 only) and repair partitions,
partition tables and boot sectors;
- mount any kind of medium;
- establish an Ethernet network connection and telnet
or ftp into another machine;
- install RPM packages;
- load and unload kernel modules and
- do all that with a keyboard map and console font
of your choice.
You see there's hardly an accident you can't fix with
this system, provided you know how these tools work. And there's the catch:
the rescue system does not contain any form of documentation, apart from
the '--help' option which just displays an overview on the command's syntax,
if at all.
You are not supposed to learn the options of these programs by heart, instead
get a good and short command reference, like Hekman's 'Linux in a Nutshell'
or Petron's 'Essential Reference'. If you can't spare the money, print out
the man pages to the most important commands. There's also an online man page repository with a search
interface.
Notice:
- USB-only keyboards do not work. If your USB keyboard
comes with a second PS/2 plug, put that in.
- No mouse support.
- If you have more than one Linux installation, use
the 'mount' command to make sure that the rescue system has mounted the right
partitions.
- You are root during your entire 'rescue' session.
Be careful.
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 Other rescue
systems
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