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

NAME
     rtprio, rtprio_thread - examine or modify realtime or idle priority

LIBRARY
     Standard C Library (libc, -lc)

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

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

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

DESCRIPTION
     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
     thread.

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

     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
     form:

     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.

RETURN VALUES
     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.

ERRORS
     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 priority.
                        Only root is allowed to change the realtime or idle
                        priority of any thread.  Exceptional privileges can be
                        granted through the mac_priority(4) policy and the
                        realtime and idletime user groups.  The sysctl(8)
                        variable security.bsd.unprivileged_idprio is
                        deprecated.  If set to non-zero, it lets any user
                        change the idle priority of threads they own.

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

SEE ALSO
     nice(1), ps(1), rtprio(1), setpriority(2), nice(3), mac_priority(4),
     renice(8), p_cansee(9)

AUTHORS
     The original author was Henrik Vestergaard Draboel <hvd@terry.ping.dk>.
     This implementation in FreeBSD was substantially rewritten by David
     Greenman.  The rtprio_thread() system call was implemented by David Xu.

FreeBSD 13.1-RELEASE-p6        December 8, 2021        FreeBSD 13.1-RELEASE-p6