Tunable Kernel Parameters

Overview
Tunable Kernel Parameters
Chapter 1
11
Tunable Kernel Parameters
Tunables (or configurable kernel parameters) are kernel variables that allow the
operating system to be configured to fit specific system needs, resulting in better
performance and/or more efficient allocation of resources. The ideal value for each
parameter is often determined by the system's particular hardware configuration, the
specific mix of applications the system runs, and the trustworthiness of system users;
factors that vary widely from system to system.
HP attempts to provide reasonable default parameter settings, but it may be necessary
or beneficial to modify these settings to better suit the needs of your particular system's
users. Refer to the individual manpage to obtain detailed information about any
configurable kernel parameter.
Individual parameters usually pertain to a specific subsystem; some are independent,
but others are interrelated or interact with each other. The parameter descriptions are
grouped according to subsystem in “Tunables by Subsystem” on page 10.
IMPORTANT All HP-UX tunable kernel parameters are release-specific. They may be added, removed,
or have their meanings changed in future releases of HP-UX.
The tunable parameters described in this manual are specific to HP-UX Release 11i
Version 1.6. Though most of the names are the same as those in the previous releases,
the behavior of specific tunables may differ significantly from previous releases.
As technological advances expand system size and capabilities, it is not uncommon for
maximum and/or default values of certain parameters to change between releases or to
vary between 32-bit and 64-bit processors. The information provided in this manual is
believed to be accurate as of the time it was written. However, system changes may
occasionally result in differences between this manual and what is actually present on
your system.
CAUTION Changing kernel parameters to improper or inappropriate values or combinations of
values can cause data loss, system panics, and other (possibly very obscure and/or
difficult to diagnose) operating anomalies.
• Read the documentation. Before altering the value of any configurable kernel
parameter, be sure you know the implications of making the change.
• Keep records. Write down the parameter name and its old value as well as the new
value in case you need to restore the old value.
• Check ranges. Never set any system parameter to a value outside the allowable
range for the parameter. (SAM refuses to store values outside the allowable range.)
• Be aware of side effects. Many parameters interact, and their values must be selected
in a balanced way.