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Linux 2.6 - man page for getpriority (linux section 3posix)

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

       getpriority, setpriority - get and set the nice value

       #include <sys/resource.h>

       int getpriority(int which, id_t who);
       int setpriority(int which, id_t who, int value);

       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,  indi-
       cating  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  schedul-
       ing.  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 algo-
       rithm 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

       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.

       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 argu-
	      ment 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

       EACCES A request was made to change the nice value to a lower numeric value and	the  cur-
	      rent process does not have appropriate privileges.

       The following sections are informative.

   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);

       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}



       nice()  , sched_get_priority_max() , sched_setscheduler() , the Base Definitions volume of
       IEEE Std 1003.1-2001, <sys/resource.h>

       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				   GETPRIORITY(P)

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