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13.6 Data Problems
Data problems are when the machine might or might not boot properly but, in either case, it
is clear that there is data corruption on the system and that the system needs to be recovered.
These situations call for a backup of your critical data, enabling you to recover a system state
from before your system failed. openSUSE offers dedicated YaST modules for system backup
and restoration as well as a rescue system that can be used to recover a corrupted system from
the outside.
13.6.1 Backing Up Critical Data
System backups can be easily managed using the YaST System Backup module:
-
As root, start YaST and select .
-
Create a backup profile holding all details needed for the backup, filename of the
archive file, scope, and type of the backup:
-
Select .
-
Enter a name for the archive.
-
Enter the path to the location of the backup if you want to keep a local backup. For
your backup to be archived on a network server (via NFS), enter the IP address or name of
the server and the directory that should hold your archive.
-
Determine the archive type and click .
-
Determine the backup options to use, such as whether files not belonging to any
package should be backed up and whether a list of files should be displayed prior to
creating the archive. Also determine whether changed files should be identified using the
time-consuming MD5 mechanism.
Use to enter a dialog for the backup of entire hard disk
areas. Currently, this option only applies to the Ext2 file system.
-
Finally, set the search constraints to exclude certain system areas from the backup
area that do not need to be backed up, such as lock files or cache files. Add, edit, or
delete items until your needs are met and leave with .
-
Once you have finished the profile settings, you can start the backup right away with
or configure automatic backup. It is also possible to create
other profiles tailored for various other purposes.
To configure automatic backup for a given profile, proceed as follows:
-
Select from the menu.
-
Select .
-
Determine the backup frequency. Choose ,
, or .
-
Determine the backup start time. These settings depend on the backup frequency selected.
-
Decide whether to keep old backups and how many should be kept. To receive an
automatically generated status message of the backup process, check .
-
Click to apply your settings and have the first backup start at
the time specified.
13.6.2 Restoring a System Backup
Use the YaST System Restoration module to restore the system configuration from a
backup. Restore the entire backup or select specific components that were corrupted and need to
be reset to their old state.
-
Start .
-
Enter the location of the backup file. This could be a local file, a network mounted
file, or a file on a removable device, such as a floppy or a CD. Then click
.
The following dialog displays a summary of the archive properties, such as the filename,
date of creation, type of backup, and optional comments.
-
Review the archived content by clicking . Clicking
returns you to the dialog.
-
opens a dialog in which to fine-tune the restore process.
Return to the dialog by clicking .
-
Click to open the view of packages to restore. Press
to restore all files in the archive or use the various
, , and buttons to fine-tune your selection. Only use the option if the RPM database is corrupted or deleted and this file is
included in the backup.
-
After you click , the backup is restored. Click
to leave the module after the restore process is completed.
13.6.3 Recovering a Corrupted System
There are several reasons why a system could fail to come up and run
properly. A corrupted file system after a system crash, corrupted
configuration files, or a corrupted boot loader configuration are the most
common ones.
openSUSE offers two different methods to cope with this kind of situation.
You can either use the YaST System Repair functionality or boot the
rescue system. The following sections cover both flavors of system repair.
Using YaST System Repair
Before launching the YaST System Repair module, determine in which mode
to run it to best fit your needs. Depending on the severeness and cause of
your system failure and your expertise, there are three different modes to
choose from:
- Automatic Repair
-
If your system failed due to an unknown cause and you basically do not
know which part of the system is to blame for the failure, use
. An extensive automated check will
be performed on all components of your installed system. For a detailed
description of this procedure, refer to Automatic Repair.
- Customized Repair
-
If your system failed and you already know which component is to blame,
you can cut the lengthy system check with short by limiting the scope of the system analysis to
those components. For example, if the system messages prior to the
failure seem to indicate an error with the package database, you can
limit the analysis and repair procedure to checking and restoring this
aspect of your system. For a detailed description of this procedure,
refer to Customized Repair.
- Expert Tools
-
If you already have a clear idea of what component failed and how this
should be fixed, you can skip the analysis runs and directly apply the
tools necessary for the repair of the respective component. For details,
refer to Expert Tools.
Choose one of the repair modes as described above and proceed with the
system repair as outlined in the following sections.
Automatic Repair
To start the automatic repair mode of YaST System Repair, proceed as
follows:
-
Insert the first installation medium of openSUSE into your CD or DVD
drive.
-
Reboot the system.
-
At the boot screen, select .
-
Confirm the license agreement and click .
-
In , select
.
-
Select .
YaST now launches an extensive analysis of the installed system. The
progress of the procedure is displayed at the bottom of the screen with
two progress bars. The upper bar shows the progress of the currently
running test. The lower bar shows the overall progress of the
analysis. The log window in the top section tracks the currently
running test and its result. See Figure 13-2.
The following main test runs are performed with every run. They
contain, in turn, a number of individual subtests.
- Check Partition Tables
-
Checks the validity and coherence of the partition tables of all
detected hard disks.
- Check Swap Areas
-
The swap partitions of the installed system are detected, tested,
and offered for activation where applicable. This offer should be
accepted for the sake of a higher system repair speed.
- Check File Systems
-
All detected file systems are subjected to a file
system–specific check.
- Check fstab Entries
-
The entries in the file are checked for completeness and consistency.
All valid partitions are mounted.
- Check Package Database
-
This checks whether all packages necessary for the operation of a
minimal installation are present. While it is optionally possible
also to analyze the base packages, this takes a long time because of
their vast number.
- Check Boot Loader Configuration
-
The boot loader configuration of the installed system (GRUB or LILO)
is checked for completeness and coherence. Boot and root devices are
examined and the availability of the initrd modules is checked.
-
Whenever an error is encountered, the procedure stops and a dialog
opens outlining the details and possible solutions.
Read the screen messages carefully before accepting the proposed fix.
If you decide to decline a proposed solution, your system remains
unchanged.
-
After the repair process has been terminated successfully, click
and and remove the
installation media. The system automatically reboots.
Customized Repair
To launch the mode and selectively
check certain components of your installed system, proceed as follows:
-
Insert the first installation medium of openSUSE into your CD or DVD
drive.
-
Reboot the system.
-
At the boot screen, select .
-
Confirm the license agreement and click .
-
In , select
.
-
Select .
Choosing shows a list of test runs
that are all marked for execution at first. The total range of tests
matches that of automatic repair. If you already know where no damage
is present, unmark the corresponding tests. Clicking
starts a narrower test procedure that probably
has a significantly shorter running time.
Not all test groups can be applied individually. The analysis of the
fstab entries is always bound to an examination of the file systems,
including existing swap partitions. YaST automatically resolves such
dependencies by selecting the smallest number of necessary test runs.
-
Whenever an error is encountered, the procedure stops and a dialog
opens outlining the details and possible solutions.
Read the screen messages carefully before accepting the proposed fix.
If you decide to decline a proposed solution, your system remains
unchanged.
-
After the repair process has been terminated successfully, click
and and remove the
installation media. The system automatically reboots.
Expert Tools
If you are knowledgeable with openSUSE and already have a very clear
idea of what needs to be repaired in your system, directly apply the
tools skipping the system analysis.
To make use of the feature of the
YaST System Repair module, proceed as follows:
-
Insert the first installation medium of openSUSE into your CD or DVD
drive.
-
Reboot the system.
-
At the boot screen, select .
-
Confirm the license agreement and click .
-
In , select
.
-
Select and choose a repair option.
-
After the repair process has been terminated successfully, click
and and remove the
installation media. The system automatically reboots.
The provides the following options to
repair your faulty system:
-
-
This starts the YaST boot loader configuration module. Find details
in Section 13.3, Configuring the Boot Loader with YaST, (↑ Reference ).
-
-
This starts the expert partitioning tool in YaST.
-
-
This checks the file systems of your installed system. You are first
offered a selection of all detected partitions and can then choose the
ones to check.
-
-
It is possible to attempt to reconstruct damaged partition tables. A
list of detected hard disks is presented first for selection. Clicking
starts the examination. This can take a while
depending on the processing power and size of the hard disk.
IMPORTANT:
Reconstructing a Partition Table
The reconstruction of a partition table is tricky. YaST attempts to
recognize lost partitions by analyzing the data sectors of the hard
disk. The lost partitions are added to the rebuilt partition table
when recognized. This is, however, not successful in all imaginable
cases.
-
-
This option saves important system files to a floppy disk. If one of
these files becomes damaged, it can be restored from disk.
-
-
This checks the consistency of the package database and the
availability of the most important packages. Any damaged installed
packages can be reinstalled with this tool.
Using the Rescue System
openSUSE contains a rescue system. The rescue system is a small Linux
system that can be loaded into a RAM disk and mounted as root file system,
allowing you to access your Linux partitions from the outside. Using the
rescue system, you can recover or modify any important aspect of your
system:
-
Manipulate any type of configuration file.
-
Check the file system for defects and start automatic repair
processes.
-
Access the installed system in a change root environment
-
Check, modify, and reinstall the boot loader configuration
-
Resize partitions using the parted command. Find more information about
this tool at the Web site of GNU Parted (https://www.gnu.org/software/parted/parted.html).
The rescue system can be loaded from various sources and locations. The
simplest option is to boot the rescue system from the original
installation CD or DVD:
IMPORTANT: No rescue system on 64bit (x86-64) installation CDs
Due to lack of space, the installation CDs for 64bit (x86-64) do not
contain a rescue system. Either get a x86-64 network installation Mini CD
(44 MB) from https://software.opensuse.org/ or start the
rescue system from a network source as described below .
-
Insert the installation medium into your CD or DVD drive.
-
Reboot the system.
-
At the boot screen, press F4 and choose
. Then choose from the main menu.
-
Enter root at the Rescue: prompt.
A password is not required.
If your hardware setup does not include a CD or DVD drive, you can boot
the rescue system from a network source (including
the openSUSE FTP server). The following example applies to a
remote boot scenario—if using another boot medium, such as a floppy
disk, modify the info file accordingly and boot as
you would for a normal installation.
-
Enter the configuration of your PXE boot setup and replace
install=protocol://instsource
with
rescue=protocol://instsource.
As with a normal installation, protocol
stands for any of the supported network protocols (NFS, HTTP, FTP, etc.)
and instsource for the path to your network
installation source.
-
Boot the system using Wake on LAN , as described in
Section 1.3.7, Wake on LAN, (↑ Reference ).
-
Enter root at the Rescue:
prompt. A password is not required.
Once you have entered the rescue system, you can make use of the virtual
consoles that can be reached with
Alt+F1
to
Alt+F6.
A shell and many other useful utilities, such as the mount program, are
available in the /bin directory. The
sbin directory contains important file and network
utilities for reviewing and repairing the file system. This directory also
contains the most important binaries for system maintenance, such as
fdisk, mkfs, mkswap, mount, mount, init, and shutdown, and ifconfig, ip,
route, and netstat for maintaining the network. The directory
/usr/bin contains the vi editor, find, less, and ssh.
To see the system messages, either use the command dmesg
or view the file /var/log/messages.
Checking and Manipulating Configuration Files
As an example for a configuration that might be fixed using the rescue
system, imagine you have a broken configuration file that prevents the
system from booting properly. You can fix this using the rescue system.
To manipulate a configuration file, proceed as follows:
-
Start the rescue system using one of the methods described above.
-
To mount a root file system located under
/dev/sda6 to the rescue system, use the following
command:
mount /dev/sda6 /mnt
All directories of the system are now located under
/mnt
-
Change the directory to the mounted root file system: cd /mnt
-
Open the problematic configuration file in the vi editor. Adjust and
save the configuration.
-
Unmount the root file system from the rescue system: umount /mnt
-
Reboot the machine.
Repairing and Checking File Systems
Generally, file systems cannot be repaired on a running system. If you
encounter serious problems, you may not even be able to mount your root
file system and the system boot may end with a kernel
panic . In this case, the only way is to repair the system from
the outside. It is strongly recommended to use the YaST System Repair for
this task (see Using YaST System Repair for details). However, if you
need to do a manual file system check or repair, boot the rescue system.
It contains the utilities to check and repair the
ext2, ext3,
reiserfs, xfs,
dosfs, and vfat file systems.
Accessing the Installed System
If you need to access the installed system from the rescue system to, for
example, modify the boot loader configuration, or to execute a hardware
configuration utility, you need to do this in a change
root environment.
To set up a change root environment based on the
installed system, proceed as follows:
-
First mount the root partition from the installed system and the device
file system:
mount /dev/sda6 /mnt
mount --bind /dev /mnt/dev
-
Now you can change root into the new environment:
chroot /mnt
-
Then mount /proc and /sys:
mount /proc
mount /sys
-
Finally, mount the remaining partitions from the installed system:
mount -a
-
Now you have access to the installed system. Before rebooting the
system, unmount the partitions with umount
-a and leave the change root
environment with exit.
WARNING: Limitations
Although you have full access to the files and applications of the
installed system, there are some limitations. The kernel that is running
is the one that was booted with the rescue system. It only supports
essential hardware and it is not possible to add kernel modules from the
installed system unless the kernel versions are exactly the same (which
is unlikely). So you cannot access a sound card, for example. It is also
not possible to start a graphical user interface.
Also note that you leave the change root environment when
you switch the console with
Alt+F1 to
Alt+F6.
Modifying and Reinstalling the Boot Loader
Sometimes a system cannot boot because the boot loader configuration is
corrupted. The start-up routines cannot, for example, translate physical
drives to the actual locations in the Linux file system without a working
boot loader.
To check the boot loader configuration and reinstall the boot loader,
proceed as follows:
-
Perform the necessary steps to access the installed system as described
in Accessing the Installed System.
-
Check whether the following files are correctly configured according to
the GRUB configuration principles outlined in Section 13.0, The Boot Loader, (↑ Reference ).
-
/etc/grub.conf
-
/boot/grub/device.map
-
/boot/grub/menu.lst
Apply fixes to the device mapping (device.map)
or the location of the root partition and configuration files, if
necessary.
-
Reinstall the boot loader using the following command sequence:
grub --batch < /etc/grub.conf
-
Unmount the partitions, log out from the change root
environment, and reboot the system:
umount -a
exit
reboot
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