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This manual page is part of the POSIX Programmer's Manual. The Linux implementation of
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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 .