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



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

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 follow-
       ing 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  pertain-
       ing  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 sys-
       tem'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 consid-
       ered  an error. A process which subsequently reverts to SCHED_OTHER need not have its priority affected by such a setpri-
       ority() 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  appro-
              priate 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, Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                               GETPRIORITY(3P)