freebsd/usr.sbin/rtprio/rtprio.1

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.Dd July 23, 1994
.Dt RTPRIO 1
.Os 
.Sh NAME
.Nm rtprio ,
.Nm idprio
.Nd execute, examine or modify a utility's or process's realtime 
or idletime scheduling priority
.Sh SYNOPSIS
.Nm [id|rt]prio
.Nm [id|rt]prio 
.Ar [-]pid
.Nm [id|rt]prio 
.Ar priority
.Ar command
.Op args
.Nm [id|rt]prio 
.Ar priority
.Ar -pid
.Nm [id|rt]prio 
.Fl t
.Ar command
.Op args
.Nm [id|rt]prio 
.Fl t
.Ar -pid
.Sh DESCRIPTION
.Nm Rtprio
is used for controlling realtime process scheduling. 
.Pp
.Nm Idprio
is used for controlling idletime process scheduling, and can be called
with the same options as 
.Nm .
.Pp
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.
.Pp
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.
.Pp
.Nm Rtprio 
or
.Nm idprio 
when called without arguments will return the realtime priority
of the current process.
.Pp
If
.Nm
is called with 1 argument, it will return the realtime priority
of the process with the specified
.Ar pid .
.Pp
If 
.Ar priority
is specified, the process or program is run at that realtime priority.
If 
.Fl t
is specified, the process or program is run as a normal (non-realtime)
process. 
.Pp
If
.Ar -pid
is specified, the process with the process identifier
.Ar pid
will be modified, else if
.Ar command 
is specified, that program is run with its arguments.
.Pp
.Ar Priority
is an integer between 0 and RTP_PRIO_MAX (usually 31). 0 is the
highest priority
.Pp
.Ar Pid
of 0 means "the current process".
.Pp
Only root is allowed to set realtime or idle priority for a process.
.Sh DIAGNOSTICS
If
.Nm
execute a command, the exit value is that of the command executed.
In all other cases,
.Nm
exits 0 on success, and 1 for all other errors.
.Sh EXAMPLES
To see which realtime priority the current process is at:
.Bd -literal -offset indent -compact
.Sy "rtprio"
.Ed
.Pp
To see which realtime priority of process
.Em 1423 :
.Bd -literal -offset indent -compact
.Sy "rtprio 1423"
.Ed
.Pp
To run
.Xr cron 8
at the lowest realtime priority:
.Bd -literal -offset indent -compact
.Sy "rtprio 31 cron"
.Ed
.Pp
To change the realtime priority of process
.Em 1423
to
.Em 16 :
.Bd -literal -offset indent -compact
.Sy "rtprio 16 -1423"
.Ed
.Pp
To run
.Xr tcpdump 1
without realtime priority:
.Bd -literal -offset indent -compact
.Sy "rtprio -t tcpdump"
.Ed
.Pp
To change the realtime priority of process
.Em 1423
to
.Dv RTP_PRIO_NORMAL
(non-realtime/normal priority):
.Bd -literal -offset indent -compact
.Sy "rtprio -t -1423"
.Ed
.Pp
To make depend while not disturbing other machine usage:
.Bd -literal -offset indent -compact
.Sy "idprio 31 make depend"
.Ed
.Sh SEE ALSO
.Xr nice 1 ,
.Xr ps 1 ,
.Xr rtprio 2 ,
.Xr setpriority 2 ,
.Xr nice 3 ,
.Xr renice 8
.Sh HISTORY
The
.Nm
utility appeared in
.Fx 2.0 ,
but is similar to the HP-UX version.
.Sh CAVEATS
You can lock yourself out of the system by placing a cpu-heavy
process in a realtime priority.
.Sh BUGS
There is no way to set/view the realtime priority of process 0
(swapper) (see
.Xr ps 1 ) .
.Pp
There is in
.Fx
no way to ensure that a process page is present in memory therefore
the process may be stopped for pagein (see
.Xr mprotect 2 ,
.Xr madvise 2 ) .
.Pp
Under
.Fx
system calls are currently never preempted, therefore non-realtime
processes can starve realtime processes, or idletime processes can
starve normal priority processes.
.Sh AUTHORS
.An -nosplit
.An Henrik Vestergaard Draboel Aq hvd@terry.ping.dk
is the original author.
This
implementation in
.Fx
was substantially rewritten by
.An David Greenman .