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getpriority(2) - getpriority, setpriority, getpriority, setpriority - get/set program scheduling priority - man 2 getpriority

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



NAME
       getpriority, setpriority - get/set(7,n,1 builtins) 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(7,n,1 builtins) 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(1,8) the range -20  to  20  (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  specified
       value.  Only the super-user may lower priorities.

RETURN VALUE
       Since getpriority can legitimately return the value -1, it is necessary
       to clear(1,3x,3x clrtobot) the external variable errno prior to the call, then  check  it
       afterwards to determine if(3,n) a -1 is an error(8,n) or a legitimate value.  The
       setpriority call returns 0 if(3,n) there is no error(8,n), or -1 if(3,n) 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  (on
              Linux systems) the caller did not have the CAP_SYS_NICE capabil-
              ity.

       EACCES A non super-user attempted to lower a process priority.

NOTES
       The details on the condition for EPERM depend on the system.  The above
       description  is  what SUSv3 says, and seems to be followed on all SYSV-
       like systems.  Linux requires the real or  effective  user  ID  of  the
       caller to match the real user of the process who (instead of its effec-
       tive user ID).  All BSD-like systems (SunOS 4.1.3, Ultrix 4.2, BSD 4.3,
       FreeBSD  4.3,  OpenBSD-2.5,  ...)  require the effective user ID of the
       caller to match the real or effective user ID of the process who.

       The actual priority range varies between kernel versions.  Linux before
       1.3.36  had -infinity..15. Linux since 1.3.43 has -20..19, and the sys-
       tem call getpriority returns 40..1 for  these  values  (since  negative
       numbers are error(8,n) codes).  The library call converts N into 20-N.

       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(1,8) <sys/time.h>.)

CONFORMING TO
       SVr4, 4.4BSD (these function calls first appeared in(1,8) 4.2BSD).

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



BSD Man Page                      2002-06-21                    GETPRIORITY(2)

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