Reboot tuning procedure

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Parameters of type Bosboot are set by the bosboot command, which retrieves their values from the nextboot file when creating a new boot image.

Parameters of type Reboot are set during the reboot process by the appropriate configuration methods, which also retrieve the necessary values from the nextboot file. In both cases, if there is no nextboot file, the parameters will be set to their default values. All other parameters are set using the following process:
  1. When tunrestore -R is called, any tunable changed from its default value is logged in the lastboot.log file. The parameters of type Reboot and Bosboot present in the nextboot file, and which should already have been changed by the time tunrestore -R is called, will be checked against the value in the file, and any difference will also be logged.
  2. The lastboot file will record all the tunable parameter settings, including default values, which will be flagged using # DEFAULT VALUE, and the AIX_level, Kernel_type, Last_validation, and Logfile_checksum fields will be set appropriately.
  3. If there is no /etc/tunables/nextboot file, all tunable parameters, except those of type Bosboot, will be set to their default value, a nextboot file with only an info stanza will be created, and the following warning: "cannot access the /etc/tunables/nextboot file" will be printed in the log file. The lastboot file will be created as described in step 2.
  4. If the desired value for a parameter is found to be out of range, the parameter will be left to its default value, and a message similar to the following: "Parameter A could not be set to X, which is out of range, and was left to its current value (Y) instead" will be printed in the log file. Similarly, if a set of interdependent parameters have values incompatible with each other, they will all be left at their default values and a message similar to the following: "Dependent parameter A, B and C could not be set to X, Y and Z because those values are incompatible with each other. Instead, they were left to their current values (T, U and V)" will be printed in the log file.

    All of these error conditions could exist if a user modified the /etc/tunables/nextboot file with an editor or copied it from another machine, possibly running a different version of AIX® with different valid ranges, and did not run tuncheck -r -f on the file. Alternatively, tuncheck -r -f prompted the user to run bosboot, but this was not done.