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RTPRIO(2)		       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 op-
     erate 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  op-
     erate 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  priori-
     ties,  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 pri-
     ority,  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	success-
     ful;  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 pri-
			ority of any  thread.	Exceptional  privileges  can  be
			granted through the mac_priority(4) policy and the real-
			time  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  visi-
			ble.

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 ports 15.quarterly	December 8, 2021		       RTPRIO(2)

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