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GETPRIORITY(2)		   Linux Programmer's Manual		GETPRIORITY(2)

NAME
       getpriority, setpriority - get/set program scheduling priority

SYNOPSIS
       #include <sys/time.h>
       #include <sys/resource.h>

       int getpriority(int which, int who);
       int setpriority(int which, int who, int prio);

DESCRIPTION
       The  scheduling	priority  of  the  process, process group, or user, as
       indicated by which and who is obtained with the getpriority() call  and
       set with the setpriority() call.

       The  value  which  is one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER, and
       who  is	interpreted  relative  to  which  (a  process  identifier  for
       PRIO_PROCESS, process group identifier for PRIO_PGRP, and a user ID for
       PRIO_USER).  A zero value for who denotes  (respectively)  the  calling
       process,	 the process group of the calling process, or the real user ID
       of the calling process.	Prio is a value in the range -20  to  19  (but
       see  the	 Notes	below).	  The  default priority is 0; lower priorities
       cause more favorable scheduling.

       The getpriority() call returns the highest priority  (lowest  numerical
       value)  enjoyed	by  any of the specified processes.  The setpriority()
       call sets the priorities of all of the specified processes to the spec‐
       ified value.  Only the superuser may lower priorities.

RETURN VALUE
       Since  getpriority() can legitimately return the value -1, it is neces‐
       sary to clear the external variable errno prior to the call, then check
       it  afterwards  to determine if a -1 is an error or a legitimate value.
       The setpriority() call returns 0 if there is no error, or -1  if	 there
       is.

ERRORS
       EINVAL which was not one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER.

       ESRCH  No process was located using the which and who values specified.

       In addition to the errors indicated above, setpriority() may fail if:

       EPERM  A	 process  was located, but its effective user ID did not match
	      either the effective or the real user ID of the caller, and  was
	      not privileged (on Linux: did not have the CAP_SYS_NICE capabil‐
	      ity).  But see NOTES below.

       EACCES The caller attempted to lower a process priority,	 but  did  not
	      have  the	 required  privilege  (on  Linux:  did	not  have  the
	      CAP_SYS_NICE capability).	 Since Linux 2.6.12, this  error  only
	      occurs  if the caller attempts to set a process priority outside
	      the range of the RLIMIT_NICE soft resource limit of  the	target
	      process; see getrlimit(2) for details.

NOTES
       A  child created by fork(2) inherits its parent's nice value.  The nice
       value is preserved across execve(2).

       The details on the condition for EPERM depend on the system.  The above
       description  is what POSIX.1-2001 says, and seems to be followed on all
       System V-like systems.  Linux kernels before 2.6.12 required  the  real
       or  effective  user  ID	of  the	 caller	 to match the real user of the
       process who (instead of its effective user ID).	Linux 2.6.12 and later
       require the effective user ID of the caller to match the real or effec‐
       tive user ID of the process who.	 All BSD-like  systems	(SunOS	4.1.3,
       Ultrix  4.2,  4.3BSD, FreeBSD 4.3, OpenBSD-2.5, ...) behave in the same
       manner as Linux >= 2.6.12.

       The actual priority range varies between kernel versions.  Linux before
       1.3.36  had  -infinity..15.   Since  kernel  1.3.43 Linux has the range
       -20..19.	 Within the kernel, nice values are actually represented using
       the  corresponding range 40..1 (since negative numbers are error codes)
       and these are the values employed by the	 setpriority()	and  getprior‐
       ity() system calls.  The glibc wrapper functions for these system calls
       handle the translations between the user-land  and  kernel  representa‐
       tions of the nice value according to the formula unice = 20 - knice.

       On some systems, the range of nice values is -20..20.

       Including <sys/time.h> is not required these days, but increases porta‐
       bility.	(Indeed, <sys/resource.h> defines the  rusage  structure  with
       fields of type struct timeval defined in <sys/time.h>.)

CONFORMING TO
       SVr4,   4.4BSD	(these	function  calls	 first	appeared  in  4.2BSD),
       POSIX.1-2001.

SEE ALSO
       nice(1), fork(2), capabilities(7), renice(8)

BSD Man Page			  2002-09-20			GETPRIORITY(2)
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