Command Section
RTPRIO(2)                 FreeBSD System Calls Manual                RTPRIO(2)

     rtprio, rtprio_thread - examine or modify realtime or idle priority

     Standard C Library (libc, -lc)

     #include <sys/types.h>
     #include <sys/rtprio.h>

     rtprio(int function, pid_t pid, struct rtprio *rtp);

     rtprio_thread(int function, lwpid_t lwpid, struct rtprio *rtp);

     The rtprio() system call is used to lookup or change the realtime or idle
     priority of a process, or the calling thread.  The rtprio_thread() system
     call is used to lookup or change the realtime or idle priority of a

     The function argument specifies the operation to be performed.
     RTP_LOOKUP to lookup the current priority, and RTP_SET to set the

     For the rtprio() system call, the pid argument specifies the process to
     operate on, 0 for the calling thread.  When pid is non-zero, the system
     call reports the highest priority in the process, or sets all threads'
     priority in the process, depending on value of the function argument.

     For the rtprio_thread() system call, the lwpid specifies the thread to
     operate on, 0 for the calling thread.

     The *rtp argument is a pointer to a struct rtprio which is used to
     specify the priority and priority type.  This structure has the following

     struct rtprio {
             u_short type;
             u_short prio;

     The value of the type field may be RTP_PRIO_REALTIME for realtime
     priorities, RTP_PRIO_NORMAL for normal priorities, and RTP_PRIO_IDLE for
     idle priorities.  The priority specified by the prio field ranges between
     0 and RTP_PRIO_MAX (usually 31).  0 is the highest possible priority.

     Realtime and idle priority is inherited through fork() and exec().

     A realtime thread can only be preempted by a thread of equal or higher
     priority, or by an interrupt; idle priority threads will run only when no
     other real/normal priority thread is runnable.  Higher real/idle priority
     threads preempt lower real/idle priority threads.  Threads of equal
     real/idle priority are run round-robin.

     The rtprio() and rtprio_thread() functions return the value 0 if
     successful; otherwise the value -1 is returned and the global variable
     errno is set to indicate the error.

     The rtprio() and rtprio_thread() system calls will fail if:

     [EFAULT]           The rtp pointer passed to rtprio() or rtprio_thread()
                        was invalid.

     [EINVAL]           The specified prio was out of range.

     [EPERM]            The calling thread is not allowed to set the realtime
                        priority.  Only root is allowed to change the realtime
                        priority of any thread, and non-root may only change
                        the idle priority of threads the user owns, when the
                        sysctl(8) variable security.bsd.unprivileged_idprio is
                        set to non-zero.

     [ESRCH]            The specified process or thread was not found or

     nice(1), ps(1), rtprio(1), setpriority(2), nice(3), renice(8),

     The original author was Henrik Vestergaard Draboel <[email protected]>.
     This implementation in FreeBSD was substantially rewritten by David
     Greenman.  The rtprio_thread() system call was implemented by David Xu.

FreeBSD 11.1-RELEASE-p4        December 27, 2011       FreeBSD 11.1-RELEASE-p4
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