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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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GETPRIORITY(3P) POSIX Programmer's Manual GETPRIORITY(3P)
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.
getpriority, setpriority — get and set the nice value
#include <sys/resource.h>
int getpriority(int which, id_t who);
int setpriority(int which, id_t who, int value);
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.
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.
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.
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);
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].
None.
None.
nice(3p), sched_get_priority_max(3p), sched_setscheduler(3p)
The Base Definitions volume of POSIX.1‐2017, sys_resource.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/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 .
IEEE/The Open Group 2017 GETPRIORITY(3P)
Pages that refer to this page: sys_resource.h(0p), nice(3p), setpriority(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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