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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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.1-2017, <sys_resource.h>

COPYRIGHT
       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(3)
