getpriority(3p) — Linux manual page


GETPRIORITY(3P)         POSIX Programmer's Manual        GETPRIORITY(3P)

PROLOG         top

       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         top

       getpriority, setpriority — get and set the nice value

SYNOPSIS         top

       #include <sys/resource.h>

       int getpriority(int which, id_t who);
       int setpriority(int which, id_t who, int value);

DESCRIPTION         top

       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

       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

       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         top

       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

ERRORS         top

       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         top

   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].

RATIONALE         top




SEE ALSO         top

       nice(3p), sched_get_priority_max(3p), sched_setscheduler(3p)

       The Base Definitions volume of POSIX.1‐2017, sys_resource.h(0p)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group               2017                   GETPRIORITY(3P)

Pages that refer to this page: sys_resource.h(0p)nice(3p)setpriority(3p)