Installing system backups

You can install the Base Operating System (BOS) using a system backup image, also called an mksysb image.

You can use a system backup to restore a corrupted operating system. Installing a system from a backup can also reduce (or even eliminate) repetitive installation and configuration tasks. For example, you can use a backup to transfer optional software installed on the source system (the machine from which you created the backup copy), in addition to the basic operating system. Also, the backup image can transfer many user configuration settings to the target system (a different machine on which you are installing the system backup).

You can install a system from a backup image that is stored on tape, CD, or DVD, or in a file.

Note: You can boot from a DVD and use a tape for the installation. However, during a tape boot, you cannot use the CD and DVD drives to supply customized information.

The procedures to install from backup operate either in prompted or nonprompted mode, depending on conditions set in the /bosinst.data file and on compatibility between the backup image and the installed machine.

When installing the backup image, the system checks whether the target system has enough disk space to create all the logical volumes stored on the backup. If there is enough space, the entire backup is recovered. Otherwise, the installation halts and the system prompts you to choose additional destination hard disks.

File systems are created on the target system at the same size as they were on the source system, unless the backup image was created with SHRINK set to yes in the image.data file, or you selected yes in the BOS Install menus. An exception is the /tmp directory, which can be increased to allocate enough space for the bosboot command. If you are installing the AIX® operating system from a system backup that uses the JFS file system, you cannot use a disk with 4K sector sizes.

When you install a system backup on the source machine, the installation program restores the Object Data Manager (ODM) on that machine. Restoring the ODM allows devices to keep the same number they had on the original system. For example, if you install two Ethernet cards in your source machine, first en0 in slot 3 and then en1 in slot 1, the cards are not renumbered if they are detected in reverse order when you install a system backup. When you clone a system backup, the installation program rebuilds the ODM on the target system after installing the image, so devices are renumbered. In both cases, the rootvg and all logical volumes have different IDs.

If you reinstall a system backup on the source machine, and the target system does not have exactly the same hardware configuration as the source system, the program might modify device attributes in the following target system files:

All files in the /etc/objrepos directory beginning with "Cu"
All files in the /dev directory

The settings in the bootlist are not restored. After a system backup restore, the bootlist is reset to the primary boot device.

Shared volume groups have AUTO ON set to no. Only user volume groups that have AUTO ON set to yes are imported. The reason for this is that shared volume groups might lock out other systems' access to the volume group because of installation queries on the shared volume group at the time of a mksysb restore operation.