HP-UX Reference (11i v1 05/09) - 2 System Calls (vol 5)

s
settune(2) settune(2)
NAME
settune - set the value of a kernel tunable parameter
SYNOPSIS
#include <sys/dyntune.h>
int settune(const char *tunable,
uint64_t value,
unsigned int flags);
DESCRIPTION
This function sets the value of the kernel tunable parameter named tunable to the supplied value. This
new value will take effect immediately, except in the cases noted below.
Some parameters cannot be changed without rebuilding the OS kernel, and then booting that rebuilt ker-
nel.
settune() will return an error [ENOTSUP] if asked to change one of these parameters.
Some parameters represent limits on resources that can be consumed by individual processes. In general,
changes to these parameters do not affect processes that are running at the time the change is made; they
affect only new programs started (with exec(2) or an equivalent) after that time. (Some specific parameters
may be exceptions to this general rule; see the documentation for those parameters in the SAM online help
for details.)
If the STF_DEFAULT flag is set in the flags parameter, the value of the tunable parameter will be set to
its hard-coded default value. In this case, the value parameter to settune() will be ignored.
The tuneinfo(2) call can give information about whether or not changes to a parameter are allowed, or will
require a reboot. Some individual parameters may have specific notes regarding their behavior when
changed; consult the online help in SAM for details on each specific parameter.
Persistence of Changes
Changes to parameter values made with settune() will remain effective across reboots. Tunable param-
eter values are stored in the Kernel Registry database. Each time the system boots, it reads the parameter
values from the database and restores them.
There is a separate Kernel Registry database for each different kernel file name. For example,
/stand/vmunix has a different set of stored parameter values than
/stand/vmunix.other. set-
tune()
always changes the database corresponding to the kernel file from which the system was last
booted. Its changes do not affect any other database.
Whenever a kernel gets rebuilt, using SAM, mk_kernel(1M), or some other method, the Kernel Registry
database will be erased and replaced with the tunable parameter values compiled into the new kernel.
Therefore, parameter changes made using settune() do not persist across kernel rebuilds. To make a
parameter change which persists across kernel rebuilds, the system files read during the kernel build
process must be updated. Use SAM or kmtune(1M) to do this.
RETURN VALUE
This function returns one of the following values:
STR_OK The value of the specified parameter has been changed. The new value is effective
immediately.
STR_PARTIAL The value of the specified parameter has been changed. However, some processes
exceeded the resource limits implied by the new parameter value. The changed
parameter value does not affect those processes or any future children of them.
STR_ERROR The function did not complete successfully. The value of the specified parameter
has not been changed.
ERRORS
If this function returns STR_ERROR to indicate an error, the global variable errno will be set to one of
the following values, to indicate the error that occurred:
[ENOENT] The specified tunable parameter does not exist.
[EFAULT] tunable specifies an address that is inaccessible.
[EPERM] The caller does not have super-user privileges.
HP-UX 11i Version 1: September 2005 − 1 − Hewlett-Packard Company Section 2−−341