Installing an alternate mksysb disk
Alternate mksysb installation involves installing a mksysb image that has already been created from a system, onto an alternate disk of the target system. The alternate disk or disks cannot contain a volume group.
When the alt_disk_mksysb command is run, the image.data file
from the mksysb image is used by default (unless a customized image.data is
given) to create the logical volumes and file systems. The prefix alt_ is
added to the logical volume names, and the file systems are created
with a prefix of /alt_inst. For example,
be created as alt_hd2, and its file system, 1,
would be created as /alt_inst/usr. These names
are changed back to their original names at the end of the alternate
disk installation process.
The mksysb image is then restored into the alternate file system. A prepopulated boot image is then copied to the boot logical volume of the altinst_rootvg, and the boot record of the boot disk is modified to allow booting from the disk.
At this point, a script can be run to allow for any customization before the system is rebooted. The alternate file systems are still mounted as /alt_inst/real_file_system (for example: /alt_inst/usr, /alt_inst/home). Files can be accessed at this point, but nothing can be installed into the alternate file system because the kernels and libraries of the mksysb image may not match those of the running system.
After the optional script is run, the file systems are unmounted,
and the logical volume and file system names are changed to match
the image.data file's names (for example, alt_inst_hd6 is
hd6 in the volume group descriptor area).
The logical volumes are exported from the Object Data Manager (ODM),
but the altinst_rootvg is only varied off. It is left in the
ODM as a placeholder so the disk is not accidentally overwritten.
The default action of the alt_disk_mksysb command
is to set the bootlist so that the next time the system boots, it
boots from this newly installed volume group. This default action
can be turned off. If specified, the system reboots at this point,
and the system reboots from the new rootvg. The boot process
proceeds to a certain point, with the new rootvg's file systems
mounted, and the bosboot command is called to rebuild
a "normal" boot logical volume. The system then reboots.
old_rootvg, and includes all disk(s) in the original rootvg. This former rootvg volume group is set to
not varyonat reboot and should only be removed with the -X flag. For example:
alt_rootvg_op -X old_rootvg
If a return to the original rootvg is necessary, the bootlist command is used to change the bootlist to reboot from the original rootvg.
If it is unclear which disk is the boot disk for a specific volume group, use the -q flag to determine the boot disk. This flag can be useful when a volume group comprises multiple disks and a change in the bootlist is necessary.