rtprio man page on HP-UX

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rtprio(2)							     rtprio(2)

       rtprio - change or read real-time priority

       The system call sets or reads the real-time priority of a process.

       If  pid is zero, it specifies the calling process; otherwise, it speci‐
       fies the process ID of a process.

       If the process pid contains more	 than  one  thread  or	a  lightweight
       process	(that  is, the process is multi-threaded), this function shall
       only change the process scheduling  policy  and	priority.   Individual
       threads	or  lightweight processes in the target process shall not have
       their scheduling policies and priorities modified.

       Note that if the target process is multi-threaded, this process	sched‐
       uling  policy and priority change will only affect a child process that
       is created later and inherits its parent's scheduling policy and prior‐
       ity.   The priority returned is the value of the target's old priority,
       though individual threads or lightweight processes may have a different
       value if some other interface is used to change an individual thread or
       lightweight processes priority.

       When setting the real-time priority of another  process,	 the  real  or
       effective  user	ID of the calling process must match the real or saved
       user ID of the process to be modified, or the effective user ID of  the
       calling	process	 must be that of a user having appropriate privileges.
       The calling process must also be a member of a privilege group allowing
       (see  getprivgrp(2))  or	 the  effective user ID of the calling process
       must be a user having appropriate privileges.

       Simply reading real-time priorities requires no special privilege.

       Real-time scheduling policies differ from normal	 timesharing  policies
       in  that	 the  real-time priority is used to absolutely order all real-
       time processes.	This priority is not degraded over  time.   All	 real-
       time  processes are of higher priority than normal user and system pro‐
       cesses, although some system processes may run at real-time priorities.
       If  there  are  several	eligible processes at the same priority level,
       they are run in a round robin fashion as long  as  no  process  with  a
       higher  priority	 intervenes.  A real-time process receives CPU service
       until it either voluntarily gives up the	 CPU  or  is  preempted	 by  a
       process	of  equal  or  higher priority.	 Interrupts can also preempt a
       real-time process.

       Valid real-time priorities run from zero to 127.	 Zero is  the  highest
       (most important) priority.  This real-time priority is inherited across
       forks (see fork(2)) and execs (see exec(2)).

       prio can have the following values:

	      Set the process to this real-time priority.

	      Do not change the real-time priority.
				  This is used to read the  process  real-time

	      Set the process to no longer have a real-time priority.
				  It resumes a normal timesharing priority.

				  Any  process,	 regardless  of	 privilege, is
				  allowed to turn off its own real-time prior‐
				  ity using a pid of zero.

   Security Restrictions
       Some or all of the actions associated with this system call are subject
       to compartmental restrictions. See compartments(5) for more information
       about  compartmentalization on systems that support that feature.  Com‐
       partmental restrictions can be overridden if the process possesses  the
       privilege Processes owned by the superuser may not have this privilege.
       Processes owned by any user may have this privilege, depending on  sys‐
       tem configuration.

       Some or all of the actions associated with this system call require one
       or more privileges.  Processes owned by the superuser have many, though
       not  all,  privileges.	Processes owned by other users may have privi‐
       lege(s), depending on system configuration.  See privileges(5) for more
       information  about  privileged  access  on  systems  that support fine-
       grained privileges.

       returns the following values:

	      The process was a real-time process.
				  The value is the  process's  former  (before
				  the call) real-time priority.

	      The process was not a real-time process.

	      An error occurred.  is set to indicate the error.

       If fails, is set to one of the following values:

	      The target process could not be accessed due to compartmental

	      prio	     is not or in the range 0 to 127.

	      The calling process is not a user
			     having  appropriate  privileges,  and neither its
			     real nor effective user  ID  match	 the  real  or
			     saved user ID of the process indicated by pid.

	      The group access list of the calling process
			     does  not	contain	 a group having capability and
			     prio is not or with a pid of zero.

	      No process can be found corresponding to that specified by

       The following call to sets the calling process to a real-time  priority
       of 90:

       Normally, compute-bound programs should not be run at real-time priori‐
       ties, because all timesharing work on the CPU would come to a  complete

       Because	processes  executing  at  real-time  priorities get scheduling
       preference over a system process executing at a lower  priority,	 unex‐
       pected  system behavior can occur after a power failure on systems that
       support power-fail recovery.  For example, when (see init(1M)) receives
       the  powerfail signal it normally reloads programmable hardware such as
       terminal multiplexers.  If a higher-priority real-time process is  eli‐
       gible  to run after the power failure, the running of is delayed.  This
       condition temporarily prevents terminal input to any process, including
       real-time  shells  of  higher  priority	than  the  eligible  real-time
       process.	 To avoid this situation, a real-time process should catch and
       suspend itself until has finished its powerfail processing.

       was developed by HP.

       rtprio(1), getprivgrp(2), nice(2), plock(2), privileges(5).


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