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This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface
may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface
may not be implemented on Linux.
NAME
getpriority, setpriority — get and set the nice value
SYNOPSIS
#include <sys/resource.h>
int getpriority(int which, id_t who);
int setpriority(int which, id_t who, int value);
DESCRIPTION
The getpriority() function shall obtain the nice value of a process, process group, or user. The
setpriority() function shall set the nice value of a process, process group, or user to value+{NZERO}.
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 an effective user ID, respectively. A 0 value
for the who argument specifies the current process, process group, or user.
The nice value set with setpriority() shall be applied to the process. If the process is multi-threaded,
the nice value shall affect all system scope threads in the process.
If more than one process is specified, getpriority() shall return value {NZERO} less than the lowest nice
value pertaining to any of the specified processes, and setpriority() shall set the nice values of all of
the specified processes to value+{NZERO}.
The default nice value is {NZERO}; lower nice values shall cause more favorable scheduling. While the
range of valid nice values is [0,{NZERO}*2−1], implementations may enforce more restrictive limits. If
value+{NZERO} is less than the system's lowest supported nice value, setpriority() shall set the nice
value to the lowest supported value; if value+{NZERO} is greater than the system's highest supported nice
value, setpriority() shall set the nice value to the highest supported value.
Only a process with appropriate privileges can lower its nice value.
Any processes or threads using SCHED_FIFO or SCHED_RR shall be unaffected by a call to setpriority().
This is not considered an error. A process which subsequently reverts to SCHED_OTHER need not have its
priority affected by such a setpriority() call.
The effect of changing the nice value may vary depending on the process-scheduling algorithm in effect.
Since getpriority() can return the value −1 upon successful completion, it is necessary to set errno to 0
prior to a call to getpriority(). If getpriority() returns the value −1, then errno can be checked to
see if an error occurred or if the value is a legitimate nice value.
RETURN VALUE
Upon successful completion, getpriority() shall return an integer in the range −{NZERO} to {NZERO}−1.
Otherwise, −1 shall be returned and errno set to indicate the error.
Upon successful completion, setpriority() shall return 0; otherwise, −1 shall be returned and errno set
to indicate the error.
ERRORS
The getpriority() and setpriority() functions shall fail if:
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 nice value is being changed.
EACCES A request was made to change the nice value to a lower numeric value and the current process does
not have appropriate privileges.
The following sections are informative.
EXAMPLES
Using getpriority()
The following example returns the current scheduling priority for the process ID returned by the call to
getpid().
#include <sys/resource.h>
...
int which = PRIO_PROCESS;
id_t pid;
int ret;
pid = getpid();
ret = getpriority(which, pid);
Using setpriority()
The following example sets the priority for the current process ID to −20.
#include <sys/resource.h>
...
int which = PRIO_PROCESS;
id_t pid;
int priority = -20;
int ret;
pid = getpid();
ret = setpriority(which, pid, priority);
APPLICATION USAGE
The getpriority() and setpriority() functions work with an offset nice value (nice value −{NZERO}). The
nice value is in the range [0,2*{NZERO} −1], while the return value for getpriority() and the third
parameter for setpriority() are in the range [−{NZERO},{NZERO} −1].
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
nice(), sched_get_priority_max(), sched_setscheduler()
The Base Definitions volume of POSIX.1‐2008, <sys_resource.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc
and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event
of any discrepancy between this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at
http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced
during the conversion of the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .