[ Bottom of Page | Previous Page | Next Page | Contents | Index | Library Home | Legal | Search ]

Files Reference

tunables File Format


Centralizes tunable parameter values.


Tunables files contain one or more sections, called "stanzas". A stanza is started by a line containing the stanza name followed by a colon (:). There is no marking for the end of a stanza. It simply continues until another stanza starts. Each stanza contains a set of parameter/value pairs; one pair per line. The values are surrounded by double quotes ("), and an equal sign (=) separates the parameter name from its value. A parameter/value pair must necessarily belong to a stanza. It has no meaning outside of a stanza. Two parameters sharing the same name but belonging to different stanzas are considered to be different parameters. If a parameter appears several times in a stanza, only its first occurence is used. Following occurences are simply ignored. Similarly, if a stanza appears multiple times in the file, only the first occurrence is used. Everything following a number sign (#) is considered a comment and ignored. Heading and trailing blanks are also ignored.

A tunable file uses the following syntax:

# first stanza
    param1 = "value1"
    param2 = "value2"
    param2 = "value3" # ignored, since already defined

# another stanza
    param1 = "value4" # not the same parameter as param1 in stanza1

# the first stanza again
stanza1: # ignored since already defined

Tunables files currently support 6 different stanzas: one for each of the tunable command (schedo, vmo, ioo, no and nfso), plus a special info stanza. The five stanzas schedo, vmo, ioo, no and nfso contain tunable parameters managed by the corresponding command (see the command's man pages for the complete parameter lists).

The value can either be a numerical value or the litteral word DEFAULT, which is interpreted as this tunable's default value. It is possible that some stanza contains values for non-existent parameters (in the case a tunable file was copied from a machine running an older version of AIX and one or more tunables do not exist anymore). Both the tunrestore and the tuncheck commands will print warnings about such parameters.

The info stanza is used to store information about the purpose of the tunable file and the level of AIX on which it was validated. Any parameter is acceptable in this stanza, however, some fields have a special meaning:

Description A character string describing the tunable file. SMIT displays this field in the file selection box.
AIX_level AIX version. This field is automatically updated by tunsave and tuncheck (on success only).
Kernel_type: "UP" this is a uniprocessor kernel.
"MP" this is a multiprocessor kernel.
"MP64" this is a 64 bits multiprocessor kernel.
This field is automatically updated by tunsave and tuncheck (on success only).
Last_validation The date this file was validated for the last time, and the type of validation:
"current" the file has been validated against the current context.
"reboot" the file has been validated against the nextboot context.
This field is automatically updated by tunsave and tuncheck (on success only).
Logfile_checksum The checksum of the lastboot.log file matching this tunables file. This field is present only in the lastboot file.

Other stanzas like info, schedo, vmo, ioo, no and nfso may be present. These stanzas are simply ignored by the tunrestore command, but flagged by the tuncheck command.

Three files under /etc/tunables have special names and meaning:

nextboot This file is automatically applied at boot time. The bosboot command also get the value of Bosboot types tunables from this file. It contains all tunable settings made permanent.
lastboot This file is automatically generated at boot time. It contains the full set of tunable parameters, with their values after the last boot. Default values are marked with # DEFAULT VALUE.
lastboot.log This should be the only file in /etc/tunables that is not in the stanza format described here. It is automatically generated at boot time, and contains the logging of the creation of the lastboot file, i.e. any parameter change made is logged. Any change which could not be made (possible if the nextboot file was created manually and not validated with tuncheck) is also logged.


The following is a sample tunables file:

    Description = "Set of tunables for departmental server"
    AIX_level = "" 
    Kernel_type = "UP" 
    Last_validation = "2002-06-16 12:11:11 CDT current"

    timeslice = "2" # set timeslice to 30ms
    sched_D = "DEFAULT"

    minperm = "48538"

    iotunable = "value" 

    ipforwarding = "1"
    ipsrcrouteforward = "1"

    nfs_allow_all_signals = "0" # DEFAULT VALUE
    nfs_device_specific_bufs = "0"


All the tunable files are located in the /etc/tunables directory.

/etc/tunables/nextboot Contains the values to be applied at the next rebooting of the machine.
/etc/tunables/lastboot Contains the values for all tuning parameters after the last rebooting of the machine.
/etc/tunables/lastboot.log Contains logging information about changes made and errors encountered during the last rebooting of the machine.

Related Information

The schedo, vmo, ioo, no, tundefault, tunsave, tunrestore, tuncheck, and nfso commands.


Tuning the AIX kernel in Performance Tools and APIs Reference Guide.

[ Top of Page | Previous Page | Next Page | Contents | Index | Library Home | Legal | Search ]