getpriority(2) - Linux manual page (original) (raw)

getpriority(2) System Calls Manual getpriority(2)

NAME top

   getpriority, setpriority - get/set program scheduling priority

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <sys/resource.h>**

   **int getpriority(int** _which_**, id_t** _who_**);**
   **int setpriority(int** _which_**, id_t** _who_**, int** _prio_**);**

DESCRIPTION top

   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)](../man2/nice.2.html).

   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)](../man2/getrlimit.2.html) for details.

RETURN VALUE top

   On success, **getpriority**() returns the calling thread's nice value,
   which may be a negative number.  On error, it returns -1 and sets
   _[errno](../man3/errno.3.html)_ to indicate the error.

   Since a successful call to **getpriority**() can legitimately return
   the value -1, it is necessary to clear _[errno](../man3/errno.3.html)_ prior to the call,
   then check _[errno](../man3/errno.3.html)_ 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](../man3/errno.3.html)_ to indicate the error.

ERRORS top

   **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 HISTORY below.

   **ESRCH** No process was located using the _which_ and _who_ values
          specified.

STANDARDS top

   POSIX.1-2008.

HISTORY top

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

   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.

NOTES top

   For further details on the nice value, see [sched(7)](../man7/sched.7.html).

   _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)](../man7/sched.7.html).

   A child created by [fork(2)](../man2/fork.2.html) inherits its parent's nice value.  The
   nice value is preserved across [execve(2)](../man2/execve.2.html).

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 top

   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 top

   [nice(1)](../man1/nice.1.html), [renice(1)](../man1/renice.1.html), [fork(2)](../man2/fork.2.html), [capabilities(7)](../man7/capabilities.7.html), [sched(7)](../man7/sched.7.html)

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

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Linux man-pages 6.10 2024-07-23 getpriority(2)

Pages that refer to this page:renice(1), getrlimit(2), ioprio_set(2), nice(2), sched_rr_get_interval(2), sched_setaffinity(2), sched_setattr(2), sched_setparam(2), sched_setscheduler(2), syscalls(2), errno(3), id_t(3type), proc_pid_stat(5), systemd.exec(5), capabilities(7), credentials(7), pid_namespaces(7), pthreads(7), sched(7)