NAME

       getpriority, setpriority - get/set program scheduling priority

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <sys/resource.h>

       int getpriority(int which, id_t who);
       int setpriority(int which, id_t 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 process attribute dealt with by
       these system calls is the same attribute (also known as the "nice" value) that is dealt with by nice(2).

       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.

       The prio argument is a value in the range -20 to 19 (but see NOTES below), with  -20  being  the  highest
       priority  and  19  being the lowest priority.  Attempts to set a priority outside this range are silently
       clamped to the range.  The default priority is 0;  lower  values  give  a  process  a  higher  scheduling
       priority.

       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.

       Traditionally, only a privileged process could lower the  nice  value  (i.e.,  set  a  higher  priority).
       However, since Linux 2.6.12, an unprivileged process can decrease the nice value of a target process that
       has a suitable RLIMIT_NICE soft limit; see getrlimit(2) for details.

RETURN VALUE

       On  success,  getpriority()  returns the calling thread's nice value, which may be a negative number.  On
       error, it returns -1 and sets errno to indicate the error.

       Since a successful call to getpriority() can legitimately return the value -1, it is necessary  to  clear
       errno prior to the call, then check errno afterward to determine if -1 is an error or a legitimate value.

       setpriority() returns 0 on success.  On failure, it returns -1 and sets errno to indicate the error.

ERRORS

       EACCES The caller attempted to set a lower nice value (i.e., a higher process priority), but did not have
              the required privilege (on Linux: did not have the CAP_SYS_NICE capability).

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

       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
              capability).  But see NOTES below.

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

STANDARDS

       POSIX.1-2008.

HISTORY

       POSIX.1-2001, SVr4, 4.4BSD (these interfaces first appeared in 4.2BSD).

NOTES

       For further details on the nice value, see sched(7).

       Note: the addition of the "autogroup" feature in Linux 2.6.38 means that the nice value no longer has its
       traditional effect in many circumstances.  For details, see sched(7).

       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 Linux 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  effective 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 and later.

   C library/kernel differences
       The getpriority system call returns nice values translated to the range 40..1, since  a  negative  return
       value  would  be  interpreted  as  an error.  The glibc wrapper function for getpriority() translates the
       value back according to the formula unice = 20 - knice (thus, the 40..1  range  returned  by  the  kernel
       corresponds to the range -20..19 as seen by user space).

BUGS

       According  to  POSIX,  the  nice  value  is a per-process setting.  However, under the current Linux/NPTL
       implementation of POSIX threads, the nice value is a per-thread attribute: different threads in the  same
       process  can  have  different  nice  values.   Portable  applications  should  avoid relying on the Linux
       behavior, which may be made standards conformant in the future.

SEE ALSO

       nice(1), renice(1), fork(2), capabilities(7), sched(7)

       Documentation/scheduler/sched-nice-design.txt in the Linux kernel source tree (since Linux 2.6.23)

Linux man-pages 6.7                                2023-10-31                                     getpriority(2)