Common Behavior for Kernel Configuration Commands

Because the kernel configuration commands are part of a unified suite, they share behavior whenever possible. Shared behaviors include command line options, output formats, exit status codes, security constraints, and persistence of changes.

Common Command Line Options

Table 10-1 lists the options shared by the kernel configuration commands kconfig, kcmodule, kctune, and kclog.

Table 10-1 Common Kernel Configuration Command Line Options

Option	Description	k c o n f i g	k c m o d u l e	k c t u n e	k c l o g
`-a`	(all) Include all information in the output that is normally omitted for brevity.	o	o	o
`-b`	(backup) Specify whether or not to update the automatic backup configuration before the requested change and specify the default backup behavior for future changes.	o	o	o
`-c`	(configuration) Specify the saved configuration to manage. If omitted, manage the currently running configuration.		o	o	o
`-C`	(comment) Include a comment in the kernel configuration log file entry associated with this command invocation.	o	o	o	o
`-d`	(description) Display descriptions of each item.	o	o	o
`-D`	(difference) Display only elements for which there is a change being held for next boot.	o	o	o
`-h`	(hold) Hold the requested changes for next boot.	o	o	o
`-P`	(parse) Use the special parsable output format.	o	o	o
`-S`	(set) Display only elements that have been set to something other than default.	o	o	o
`-v`	(verbose) Display items using verbose output format.	o	o	o

Common Output Formats

When retrieving information, the primary kernel configuration commands produce output in three basic output formats: table, verbose, and parsable.

By default, the commands produce a short table format. This is a format that gives one line for each item being described. Only the most commonly used information is included, in order to allow the output to fit on one line on most terminals.

With the-v (verbose) option, the commands produce a verbose output format. This format gives all available information for each item being described, taking multiple lines to do so. A blank line separates the items in the output.

With the -P (parse) option, the commands produce an output format designed to be parsed by scripts or applications. This format is described in “Parsing Command Output”. Scripts and applications must parse this output format, because HP supports release-to-release compatibility of output format only when the -P option is used.

The kernel configuration commands all use a common format for error, warning, note, and progress messages. It is the same format used by the Software Distributor package, and therefore already familiar to most administrators.

ERROR:: This is an error message. It explains why the requested operation cannot complete.
WARNING:: This is a warning message. The requested operation completed, but not smoothly. A situation may exist that needs correction.
NOTE:: This is a note. It provides information about how the operation completed, or other information of potential interest to the administrator.
*: This is a progress message. It displays the steps completed during the operation.

Common Exit Status Codes

All of the kernel configuration commands exit with one of the following status codes.

0: The operation was successful.
1: The requested changes could not be applied to the currently running system. They are being held and will be applied at next boot.
2: The operation could not complete successfully.

Common Security Constraints

Any user can run the kernel configuration commands to query configuration information. However, access to configuration information is subject to standard UNIX file system permissions on the relevant files.

Superuser privileges are required to make any configuration changes.

Persistence of Changes

By default, the kernel configuration tools will apply configuration changes to the currently running system, causing an immediate change in behavior. System administrators can override this default by specifying the -h (hold) option on any of the commands. This option causes the changes to be held until the system is rebooted. HP recommends that this option be used only when the next reboot is expected to happen soon. If the reboot doesn't happen for months after the change, the change could come as an unwelcome surprise to an administrator who has forgotten the request.

Some configuration changes cannot be applied without a reboot. These changes will be held until the system is rebooted even if the –h option is not specified. In these cases, a warning message is printed.

If multiple configuration changes are requested in a single invocation of one of the kernel configuration commands, and any one of those changes requires a reboot, all of the requested changes will be held until the system is rebooted. In particular, if a saved kernel configuration is loaded using kconfig –l (load), and that configuration cannot be used without a reboot, the state of the running system is not changed and the specified kernel configuration will be used at next boot instead.

Changes being held for next boot can be listed using the -D (differences) option on the kcmodule, kctune, or kconfig commands.

Changes being held for next boot are discarded as follows: when the currently running configuration is replaced using kconfig –i (import), kconfig –l (load), or kconfig –n (next boot); when explicitly discarded using kconfig –H (unhold); or when subsequent changes are made that override them. For example, if you run.

# kctune –h nproc=5000  # set to 5000, hold for next boot
# kctune nproc=6000     # set to 6000, now

the value of nproc at next boot will be 6000. The change to 5000 is discarded. A warning will be printed in these situations.

Changes that are made to the currently running system are retained when the system is rebooted. They remain in effect until changed.

Common Behavior for Kernel Configuration Commands

Technical documentation

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Common Command Line Options

Common Output Formats

Common Exit Status Codes

Common Security Constraints

Persistence of Changes