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 on 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
       IEEE Std 1003.1-2001, <sys/resource.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications Issue 6, Copyright (C) 2001-2003 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 .