Dynamically Tunable Parameters in HP-UX 11i

Figure 2: Determining whether a tunable parameter can be

changed without rebooting

Information about each tunable can be found in the online help system for SAM. This

data is also available on docs.hp.com. (Go to your current HP-UX release and then

search for “Configurable Kernel Parameters.”)

changing tunable

parameters with

kmtune and

mk_kernel

The kmtune(1M) command is HP-UX’s supported method for changing the values of

tunable parameters from the command line. kmtune will update the proper system file

to define a new value for a specified tunable. The next time the kernel is compiled, it will

incorporate the new value of the tunable. The administrator can compile the kernel using

mk_kernel(1M), and then reboot the system with the new kernel to complete the

change.

When kmtune is invoked with the –u flag, in addition to changing the system file,

kmtune will also change the value of the tunable being used by the currently running

kernel. In this case, no kernel rebuild or reboot is required.

using dynamic

tunable APIs

Software developers can write software which changes tunable parameters using the

settune(2) API. Such changes will remain effective only until the next time the kernel

is rebuilt, since settune() does not modify the system files like kmtune(1M) does.

The gettune(2) and tuneinfo(2) APIs can be used to retrieve information about

tunables and their current values.

persistence of

kernel tuning

Two mechanisms are used to ensure that tunable value changes remain persistent: the

system files and the Kernel Registry Service. These mechanisms keep tunable value

changes persistent across reboots, as long as the kernel is neither rebuilt nor renamed.

Depending on the method used, they may also remain persistent across kernel rebuilds.

In general, however, tunable value changes do not remain persistent when a kernel is

renamed, or when switching between two kernels with different names. The sections

below give more details.

kmtune(1M) is also capable of tuning the tunables defined by Dynamically Loadable Kernel Modules (DLKM). When changing a DLKM tunable,

the DLKM must be unloaded, recompiled, and reloaded to incorporate the new tunable value.