Tunables file directory
Information about tunable parameter values is located in the /etc/tunables directory. Except for a log file created during each reboot, this directory only contains ASCII stanza files with sets of tunable parameters.
These files contain parameter=value pairs specifying tunable parameter changes, classified in six stanzas corresponding to the six tuning commands : schedo, vmo, ioo, no, raso, and nfso. Additional information about the level of AIX®, when the file was created, and a user-provided description of file usage is stored in a special stanza in the file. For detailed information on the file's format, see the tunables file.
The main file in the tunables directory is called nextboot. It contains all the tunable parameter values to be applied at the next reboot. The lastboot file in the tunables directory contains all the tunable values that were set at the last machine reboot, a timestamp for the last reboot, and checksum information about the matching lastboot.log file, which is used to log any changes made, or any error messages encountered, during the last rebooting. The lastboot and lastboot.log files are set to be read-only and are owned by the root user, as are the directory and all of the other files.
Users can create as many /etc/tunables files as needed, but only the nextboot file
is ever automatically applied. Manually created files must be validated using the tuncheck
command. Parameters and stanzas can be missing from a file. Only tunable parameters present in the
file will be changed when the file is applied with the tunrestore command. Missing tunables
will simply be left at their current or default values. To force resetting of a tunable to its
default value with tunrestore (presumably to force other tunables to known values, otherwise
tundefault, which sets all parameters to their default value, could have been used),
DEFAULT can be specified. Specifying DEFAULT for a tunable in the
nextboot file is the same as not having it listed in the file at all because the reboot
tuning procedure enforces default values for missing parameters. This will guarantee to have all
tunables parameters set to the values specified in the nextboot file after each reboot.
Tunable files can have a special stanza named info containing the parameters AIX_level, Kernel_type and Last_validation. Those parameters are automatically set to the level of AIX and to the type of kernel (MP64) running when the tuncheck or tunsave is run on the file. Both commands automatically update those fields. However, the tuncheck command will only update if no error was detected.
The lastboot file always contains values for every tunable parameters. Tunables set to
their default value will be marked with the comment DEFAULT VALUE. Restricted
tunables modified from their default value are marked, after the value, with an additional comment
# RESTRICTED not at default value. The Logfile_checksum parameter only
exists in that file and is set by the tuning reboot process (which also sets the rest of the info
stanza) after closing the log file.
- Using SMIT to modify the next reboot value for tunable parameters, or to ask to save all current values for next boot, or to ask to use an existing tunable file at the next reboot. All those actions will update the /etc/tunables/nextboot file. A new file in the /etc/tunables directory can also be created to save all current or all nextboot values.
- Using the tuning commands (ioo, raso, vmo, schedo, no or nfso) with the -p or -r options, which will update the /etc/tunables/nexboot file.
- A new file can also be created directly with an editor or copied from another machine. Running tuncheck [-r | -p] -f must then be done on that file.
- Using the tunsave command to create or overwrite files in the /etc/tunables directory
- Using the tunrestore -r command to update the nextboot file.