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

schedsetscheduler(2) System Calls Manual schedsetscheduler(2)

NAME top

   sched_setscheduler, sched_getscheduler - set and get scheduling
   policy/parameters

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <sched.h>**

   **int sched_setscheduler(pid_t** _pid_**, int** _policy_**,**
                          **const struct sched_param ***_param_**);**
   **int sched_getscheduler(pid_t** _pid_**);**

DESCRIPTION top

   The **sched_setscheduler**() system call sets both the scheduling
   policy and parameters for the thread whose ID is specified in _pid_.
   If _pid_ equals zero, the scheduling policy and parameters of the
   calling thread will be set.

   The scheduling parameters are specified in the _param_ argument,
   which is a pointer to a structure of the following form:

       struct sched_param {
           ...
           int sched_priority;
           ...
       };

   In the current implementation, the structure contains only one
   field, _schedpriority_.  The interpretation of _param_ depends on the
   selected policy.

   Currently, Linux supports the following "normal" (i.e., non-real-
   time) scheduling policies as values that may be specified in
   _policy_:

   **SCHED_OTHER**
          the standard round-robin time-sharing policy;

   **SCHED_BATCH**
          for "batch" style execution of processes; and

   **SCHED_IDLE**
          for running _very_ low priority background jobs.

   For each of the above policies, _param->schedpriority_ must be 0.

   Various "real-time" policies are also supported, for special time-
   critical applications that need precise control over the way in
   which runnable threads are selected for execution.  For the rules
   governing when a process may use these policies, see [sched(7)](../man7/sched.7.html).
   The real-time policies that may be specified in _policy_ are:

   **SCHED_FIFO**
          a first-in, first-out policy; and

   **SCHED_RR**
          a round-robin policy.

   For each of the above policies, _param->schedpriority_ specifies a
   scheduling priority for the thread.  This is a number in the range
   returned by calling [sched_get_priority_min(2)](../man2/sched%5Fget%5Fpriority%5Fmin.2.html) and
   [sched_get_priority_max(2)](../man2/sched%5Fget%5Fpriority%5Fmax.2.html) with the specified _policy_.  On Linux,
   these system calls return, respectively, 1 and 99.

   Since Linux 2.6.32, the **SCHED_RESET_ON_FORK** flag can be ORed in
   _policy_ when calling **sched_setscheduler**().  As a result of
   including this flag, children created by [fork(2)](../man2/fork.2.html) do not inherit
   privileged scheduling policies.  See [sched(7)](../man7/sched.7.html) for details.

   **sched_getscheduler**() returns the current scheduling policy of the
   thread identified by _pid_.  If _pid_ equals zero, the policy of the
   calling thread will be retrieved.

RETURN VALUE top

   On success, **sched_setscheduler**() returns zero.  On success,
   **sched_getscheduler**() returns the policy for the thread (a
   nonnegative integer).  On error, both calls return -1, and _[errno](../man3/errno.3.html)_
   is set to indicate the error.

ERRORS top

   **EINVAL** Invalid arguments: _pid_ is negative or _param_ is NULL.

   **EINVAL** (**sched_setscheduler**()) _policy_ is not one of the recognized
          policies.

   **EINVAL** (**sched_setscheduler**()) _param_ does not make sense for the
          specified _policy_.

   **EPERM** The calling thread does not have appropriate privileges.

   **ESRCH** The thread whose ID is _pid_ could not be found.

VERSIONS top

   POSIX.1 does not detail the permissions that an unprivileged
   thread requires in order to call **sched_setscheduler**(), and details
   vary across systems.  For example, the Solaris 7 manual page says
   that the real or effective user ID of the caller must match the
   real user ID or the save set-user-ID of the target.

   The scheduling policy and parameters are in fact per-thread
   attributes on Linux.  The value returned from a call to [gettid(2)](../man2/gettid.2.html)
   can be passed in the argument _pid_.  Specifying _pid_ as 0 will
   operate on the attributes of the calling thread, and passing the
   value returned from a call to [getpid(2)](../man2/getpid.2.html) will operate on the
   attributes of the main thread of the thread group.  (If you are
   using the POSIX threads API, then use [pthread_setschedparam(3)](../man3/pthread%5Fsetschedparam.3.html),
   [pthread_getschedparam(3)](../man3/pthread%5Fgetschedparam.3.html), and [pthread_setschedprio(3)](../man3/pthread%5Fsetschedprio.3.html), instead of
   the **sched_***(2) system calls.)

STANDARDS top

   POSIX.1-2008 (but see BUGS below).

   **SCHED_BATCH** and **SCHED_IDLE** are Linux-specific.

HISTORY top

   POSIX.1-2001.

NOTES top

   Further details of the semantics of all of the above "normal" and
   "real-time" scheduling policies can be found in the [sched(7)](../man7/sched.7.html)
   manual page.  That page also describes an additional policy,
   **SCHED_DEADLINE**, which is settable only via [sched_setattr(2)](../man2/sched%5Fsetattr.2.html).

   POSIX systems on which **sched_setscheduler**() and
   **sched_getscheduler**() are available define
   **_POSIX_PRIORITY_SCHEDULING** in _<unistd.h>_.

BUGS top

   POSIX.1 says that on success, **sched_setscheduler**() should return
   the previous scheduling policy.  Linux **sched_setscheduler**() does
   not conform to this requirement, since it always returns 0 on
   success.

SEE ALSO top

   [chrt(1)](../man1/chrt.1.html), [nice(2)](../man2/nice.2.html), [sched_get_priority_max(2)](../man2/sched%5Fget%5Fpriority%5Fmax.2.html),
   [sched_get_priority_min(2)](../man2/sched%5Fget%5Fpriority%5Fmin.2.html), [sched_getaffinity(2)](../man2/sched%5Fgetaffinity.2.html), [sched_getattr(2)](../man2/sched%5Fgetattr.2.html),
   [sched_getparam(2)](../man2/sched%5Fgetparam.2.html), [sched_rr_get_interval(2)](../man2/sched%5Frr%5Fget%5Finterval.2.html), [sched_setaffinity(2)](../man2/sched%5Fsetaffinity.2.html),
   [sched_setattr(2)](../man2/sched%5Fsetattr.2.html), [sched_setparam(2)](../man2/sched%5Fsetparam.2.html), [sched_yield(2)](../man2/sched%5Fyield.2.html),
   [setpriority(2)](../man2/setpriority.2.html), [capabilities(7)](../man7/capabilities.7.html), [cpuset(7)](../man7/cpuset.7.html), [sched(7)](../man7/sched.7.html)

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

Pages that refer to this page:chrt(1), uclampset(1), getrlimit(2), gettid(2), mlock(2), nanosleep(2), PR_SET_TIMERSLACK(2const), sched_get_priority_max(2), sched_setaffinity(2), sched_setattr(2), sched_setparam(2), syscalls(2), id_t(3type), posix_spawn(3), proc_pid_stat(5), systemd.exec(5), capabilities(7), cpuset(7), credentials(7), sched(7)