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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.1‐2008, sys_resource.h(0p)
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 .
IEEE/The Open Group 2013 GETPRIORITY(3P)
Pages that refer to this page: sys_resource.h(0p), nice(3p), setpriority(3p)
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