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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 dif-
       fer (consult 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  following  values: PRIO_PROCESS, PRIO_PGRP, or PRIO_USER, indicating that the who argument is to be inter-
       preted as a process ID, a process group ID, or an effective user ID, respectively.  A 0 value for the who argu-
       ment 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 speci-
       fied 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.  Other-
       wise, -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 pro-
              cess 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 get-
       pid().


              #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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  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 .



IEEE/The Open Group                  2003                      GETPRIORITY(3P)