AIX compatibility mode

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When migrating to the compatibility mode only the no and nfso commands apply because the vmtune and schedtune commands no longer exist. You can use the compatibility mode to migrate to the new tuning framework, but it is not recommended for use with AIX® releases.

The compatibility mode allows you to make permanent changes to tunable parameters by embedding calls to tuning commands in scripts called during the boot process. The only perceivable difference is that the /etc/tunables/lastboot and /etc/tunables/lastboot.log files are created during reboot. The lastboot.log file contains a warning that says that AIX is currently running in compatibility mode and that the nextboot file has not been applied.

Except for parameters of type Bosboot (see Replacements for the vmtune and schedtune commands), neither the new reboot and permanent options, the -r and -p flags respectively, of the tuning commands are meaningful because the content of the file is not applied at reboot time. The tuning commands are not controlling the reboot values of parameters like they would in non-compatibility mode. Parameters of type Bosboot are preserved during migration, stored in the /etc/tunables/nextboot file, and can be modified using the -r option, whether you are running in compatibility mode or not. Do not delete the /etc/tunables/nextboot file.

Compatibility mode is controlled by a new sys0 attribute called pre520tune, which is automatically set to enable during a migration installation. In the disable mode, embedded calls to tuning commands in scripts called during reboot are overwritten by the content of the nextboot file. The current setting of the pre520tune attribute can be viewed by running the following command: 
# lsattr -E -l sys0
and changed either by using the following command: 
# chdev -l sys0 -a pre520tune=disable

When the compatibility mode is disabled, the following no command parameters, which are all of type Reboot, which means that they can only be changed during reboot, cannot be changed without using the -r flag:

  • arptab_bsiz
  • arptab_nb
  • extendednetstats
  • ifsize
  • inet_stack_size
  • ipqmaxlen
  • nstrpush
  • pseintrstack
Switching to non-compatibility mode while preserving the current reboot settings can be done by first changing the pre520tune attribute, and then by running the following command: 
# tunrestore -r -f lastboot

This copies the content of the lastboot file to the nextboot file. For details about the tuning mode, see the Kernel tuning section in the Performance Tools Guide and Reference.