getpriority(3C)
getpriority, setpriority --
get or set program scheduling priority
Synopsis
#include <sys/time.h>
#include <sys/resource.h>
int getpriority(int which, id_t who);
int setpriority(int which, id_t who, int priority);
Description
The getpriority function obtains the current scheduling
priority of a process, process group, or user.
The setpriority function sets the scheduling priority of a
process, process group, or user.
Target processes are specified by the values of the which and
who arguments.
The which argument may be one of the following values:
PRIO_PROCESS, PRIO_PGRP, or PRIO_USER,
indicating that the who argument is to be interpreted as a process
ID, a process group ID, or a user ID, respectively.
A 0 value for the who argument specifies the current process,
process group, or user.
If more than one process is specified, getpriority returns
the highest priority (lowest numerical value) pertaining to
any of the specified processes, and setpriority sets
the priorities of all of the specified processes to the
specified priority value.
The default priority is 0; negative priorities cause more
favorable scheduling.
If priority is less than -20, a value of -20 is used;
if it is greater than 20, a value of 20 is used.
Only a process with appropriate privileges can raise its priority
(ie. assign a lower numerical priority value).
Return values
Upon successful completion, getpriority returns an
integer in the range from -20 to 20.
Otherwise, -1 is returned and errno is set to indicate the error.
Upon successful completion, setpriority returns 0.
Otherwise, -1 is returned and errno is set to indicate the error.
Since getpriority
can legitimately return the value -1, it is necessary
to clear the external variable errno prior to the
call, then check it afterward to determine
if a -1 return is an error or a legitimate value.
Errors
getpriority and setpriority
may return one of the following errors:
ESRCH-
No process could be located using the which and
who argument values specified.
EINVAL-
The value of the which argument was not recognized, or
the value of the who argument is not a valid process ID,
process group ID, or user ID.
In addition, setpriority may fail if:
EPERM-
A process was located, but neither the real nor effective user
ID of the executing process match the effective user
ID of the process whose priority is being changed.
EACCESS-
A request was made to change the priority to a lower numeric value
(that is, to a higher priority) and the current process does not have
appropriate privileges
References
fork(2),
nice(1),
renice(1),
renice(1Mbsd)
Notices
It is not possible for the process executing setpriority
to lower any other process down to its current priority,
without requiring privileged user privileges.
getpriority, setpriority
Standards conformance
These routines conform to X/Open System Interfaces and Headers,
Issue 4, Version 2.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004