Dynamically Tunable Parameters in HP-UX 11i
4
which tunables
are dynamic?
A tunable may be either static, dynamic, or automatic:
• A static tunable is one whose value cannot be changed without rebooting the system.
Usually a kernel rebuild is also required.
• A dynamic tunable is one whose value can be changed without a reboot.
• An automatic tunable is one that is constantly being tuned by the kernel itself, in
response to changing system conditions. However, the administrator has the option
of setting a fixed value for it, like a dynamic tunable, and thus disabling the automatic
tuning algorithm.
Historically, all tunables have been static, but starting with HP-UX 11i, some tunables
are now dynamic. The list of dynamic and automatic tunables is continually growing. To
determine which tunables are dynamic on your HP-UX 11i system, use the kmtune(1M)
command, or visit the Kernel Configuration portion of SAM.
More tunables are being made dynamic as time goes by. If you want to change the value
of a tunable that is static, look to see if a kernel patch is available that makes that tunable
dynamic.
changing
tunable values
There are a number of different methods available for changing tunables. This section
describes them, arranged from the most user-friendly method (SAM) to the lowest level
method (kernel system-call APIs).
changing tunable
parameters with
SAM
SAM is HP’s System Administration Manager, a tool supplied with all HP-UX systems.
Many system administrators have used this tool for changing tunable values. SAM
handles all the necessary file changes, rebuilds the kernel, and reboots automatically.
In HP-UX 11i, SAM can be used in exactly the same way to change tunable values. Any
time a tunable is changed using SAM, it will inform the administrator whether or not that
tunable change requires a reboot. If no reboot is required, SAM will then proceed to
make the tunable change immediately.
Figure 1: SAM allows dynamic tunable parameter changes
In SAM’s Configurable Parameters screen, administrators can tell at a glance whether or
not the value of a particular tunable can be changed without a reboot. Those that can be
changed without a reboot are marked “Dynamic;” those that require a reboot are marked
“Static.”