Source:Troubleshooting Disaster Recovery: Difference between revisions

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==Disaster recovery on Linux==  
==Disaster recovery on Linux==  
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Revision as of 11:15, 16 June 2020


Template:Copyright SEP AG en

Docs latest icon.png Welcome to the latest SEP sesam documentation version 4.4.3/4.4.3 Beefalo V2. For previous documentation version(s), check documentation archive.


Disaster recovery on Linux

The recovered system does not boot

Problem

  • The system does not boot because /root/dev/console cannot be found.

Possible causes

  • Certain distributions rely on the existence of the directory /dev/ while booting
  • Certain static devices must exist before the udev daemon creates them.

Solution

  • Include the /dev/ file system in your backup.
  • If the restore cannot restore /dev/:
  1. Boot from the SEP sesam LIVE CD
  2. Mount the ROOT partition of the restored system
  3. Manually create the /dev/ directory
  4. Manually create the /dev/console entry with:
mknod /path/to/target/mount//dev/console c 0 0

No bootable operating system can be found

Problem

  • The system is not able to find a bootable OS instance after the restore.

Possible causes

  • There may have been problems during the installation of the GRUB boot loader.

Solution

  • The restore protocol includes a statement whether or not the installation of the boot loader was successful:
2009-12-14 14:48:27: sbc-3500: Info:     Reinstall boot manager
[/sesam/bin/sesam//sbc_grub_auto /mnt/disk/ AUTO]

  • It is also possible to boot the system again from the live-CD, mount the target partitions and use grub-install to install the boot loader correctly.

The device does not have a corresponding BIOS drive

Problem

  • During the restore, the following error occurs:
/dev/sda1 does not have any corresponding BIOS drive

Possible causes

  • Check the file /boot/grub/device.map on the target system. If there are entries referring to the disk through /dev/by-disk/... as shown in the example below, the entry is most likely the reference to the hard disk partition of the broken system. GRUB will not find the proper device:
hd(0) /dev/disk/by-id/ata-SAMSUNG_SP2504C_S09QJ1GLA14263-part1

Solution

  • Reboot from the live-CD
  • Mount the root and boot partitions to /mnt/disk (and /mnt/disk/boot, if necessary)
  • Restart grub-install with the following options:
grub-install --root-directory=/mnt/disk --recheck hd0

Output:

grub-probe: error: Cannot open `/boot/grub/device.map'
/usr/sbin/grub-install: line 374: [: =: unary operator expected
Installation finished. No error reported.
This is the contents of the device map /mnt/disk/boot/grub/device.map.
Check if this is correct or not. If any of the lines is incorrect,
fix it and re-run the script `grub-install'.

(hd0)   /dev/hda
(hd1)   /dev/hdb

You can ignore the error line 374: [: =: unary operator expected.
More important is the result Installation finished. No error reported.

No corresponding BIOS drive for /dev/cciss/c0d0p2

Problem

  • You receive the message: /dev/cciss/c0d0p2 does not have any corresponding BIOS drive in restore log.

Solution

fsck.ext3: File system has unsupported features

Problem

  • During a restore of a system with kernel version 2.4 the system may not boot because the Live-CD creates a file system with features which are not supported by kernel 2.4.

Possible causes

  • Most likely the file system options resize_inode,dir_index,large_file,ext_attr are causing the problem and making the system unbootable.

Solution

  • Reboot from the Live-CD image, which includes the tool debugfs.
  • Show the file system features with debugfs:
root@recover#: debugfs -w /dev/sda2
debugfs 1.41.1 (01-Sep-2008)
debugfs:  features
Filesystem features: has_journal ext_attr resize_inode dir_index filetype needs_recovery sparse_super large_file
quit

Replace /dev/sda2 with the corresponding partition names on your system.

  • To remove file system features:
root@recover#: debugfs -w /dev/sda2
debugfs:  features -resize_inode -ext_attr -dir_index -large_file -needs_recovery -sparse_super
Filesystem features: has_journal filetype
quit

After removing the options, the system should boot correctly.

Incorrect inode size (256)

Problem

  • After a successful restore the boot process stops with incorrect inode size (256).

Possible causes

  • Older kernel versions (2.4) may use a different inode size than the one the file system's created through the Live-CD (which includes kernel 2.6). For example, this happens during the restore of SLES8 based systems which use an inode size of 128k.

Solution

  • This can only be solved by formatting the devices manually from the Live-CD, using the proper mkfs options:
mkfs.ext3 -I 128 /dev/sda1

After this step, remount the partition to /mnt/disk and repeat the restore operations. Changing the inode size is only possible by reformatting the devices.

Missing root file system

Problem

  • The restored system can't find a root file system and fails during resume.

Possible causes

  • The /etc/fstab file was configured with the root file system as UUID.

Solution

  • Specify the root file system device name in conventional device names if you are using a different physical disk. After booting, use YAST to reconfigure your boot loader or edit your /boot/grub/menu.lst manually:
root=/dev/sda2

Missing network cards

Problem

  • The restored system does not find any network cards.

Possible causes

  • If the restore was done to dissimilar hardware, SLES-based distributions may not configure the network devices correctly. SLES-based systems save their network configuration by using the system's MAC address. Most likely the system will not use eht0 as a device name, but eth1, as it has another MAC address.

Solution

  • Use YaST and reconfigure your network interfaces.

See also

SEP sesam Disaster Recovery