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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 differ (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 argu-
       ments.  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 effec-
       tive 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  sys-
       tem 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 speci-
       fied  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  sup-
       ported value.
       Only a process with appropriate privileges can lower its nice value.
       Any  processes  or  threads using SCHED_FIFO or SCHED_RR shall be unaf-
       fected 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 privi-
              leges.

       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  Defi-
       nitions 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 .

IEEE/The Open Group                  2003                      GETPRIORITY(3P)