rtprio(2) [freebsd man page]

RTPRIO(2)						      BSD 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 sys-
     tem call reports the highest priority in the process, or sets all threads' priority in the process, depending on value of the function argu-
     ment.

     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 prior-
     ity.

     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 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 visible.

SEE ALSO

     nice(1), ps(1), rtprio(1), setpriority(2), nice(3), 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.

BSD
								 December 27, 2011							       BSD

RTPRIO(1)						    BSD General Commands Manual 						 RTPRIO(1)

NAME

     rtprio, idprio -- execute, examine or modify a utility's or process's realtime or idletime scheduling priority

SYNOPSIS

     [id|rt]prio
     [id|rt]prio [-]pid
     [id|rt]prio priority command [args]
     [id|rt]prio priority -pid
     [id|rt]prio -t command [args]
     [id|rt]prio -t -pid

DESCRIPTION

     The rtprio utility is used for controlling realtime process scheduling.

     The idprio utility is used for controlling idletime process scheduling, and can be called with the same options as rtprio.

     A process with a realtime priority is not subject to priority degradation, and will only be preempted by another process of equal or higher
     realtime priority.

     A process with an idle priority will run only when no other process is runnable and then only if its idle priority is equal or greater than
     all other runnable idle priority processes.

     Both rtprio or idprio when called without arguments will return the realtime priority of the current process.

     If rtprio is called with 1 argument, it will return the realtime priority of the process with the specified pid.

     If priority is specified, the process or program is run at that realtime priority.  If -t is specified, the process or program is run as a
     normal (non-realtime) process.

     If -pid is specified, the process with the process identifier pid will be modified, else if command is specified, that program is run with
     its arguments.

     Priority is an integer between 0 and RTP_PRIO_MAX (usually 31).  0 is the highest priority

     Pid of 0 means "the current process".

     Only root is allowed to set realtime or idle priority for a process.  A user may modify the idle priority of their own processes if the
     sysctl(8) variable security.bsd.unprivileged_idprio is set to non-zero.  Note that this increases the chance that a deadlock can occur if a
     process locks a required resource and then does not get to run.

EXIT STATUS

     If rtprio execute a command, the exit value is that of the command executed.  In all other cases, rtprio exits 0 on success, and 1 for all
     other errors.

EXAMPLES

     To see which realtime priority the current process is at:
	   rtprio

     To see which realtime priority of process 1423:
	   rtprio 1423

     To run cron(8) at the lowest realtime priority:
	   rtprio 31 cron

     To change the realtime priority of process 1423 to 16:
	   rtprio 16 -1423

     To run tcpdump(1) without realtime priority:
	   rtprio -t tcpdump

     To change the realtime priority of process 1423 to RTP_PRIO_NORMAL (non-realtime/normal priority):
	   rtprio -t -1423

     To make depend while not disturbing other machine usage:
	   idprio 31 make depend

SEE ALSO

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

HISTORY

     The rtprio utility appeared in FreeBSD 2.0, but is similar to the HP-UX version.

AUTHORS

     Henrik Vestergaard Draboel <hvd@terry.ping.dk> is the original author.  This implementation in FreeBSD was substantially rewritten by David
     Greenman.

CAVEATS

     You can lock yourself out of the system by placing a cpu-heavy process in a realtime priority.

BUGS

     There is no way to set/view the realtime priority of process 0 (swapper) (see ps(1)).

     There is in FreeBSD no way to ensure that a process page is present in memory therefore the process may be stopped for pagein (see
     mprotect(2), madvise(2)).

     Under FreeBSD system calls are currently never preempted, therefore non-realtime processes can starve realtime processes, or idletime pro-
     cesses can starve normal priority processes.

BSD
								September 29, 2012							       BSD