-.TH ionice "1" "August 2005" ionice
+.TH IONICE 1 "July 2011" "util-linux" "User Commands"
.SH NAME
-ionice \- get/set program io scheduling class and priority
+ionice \- set or get process I/O scheduling class and priority
.SH SYNOPSIS
.B ionice
-.RB [[ \-c
+.RB [ \-c
.IR class ]
.RB [ \-n
-.IR classdata ]
-.RB [ \-t ]]
-.BI \-p \ PID
-.RI [ PID ]...
+.IR level ]
+.RB [ \-t ]
+.B \-p
+.IR PID ...
.br
.B ionice
.RB [ \-c
.IR class ]
.RB [ \-n
-.IR classdata ]
+.IR level ]
.RB [ \-t ]
-.IR COMMAND\ [ ARG ]...
+.IR "command " [ argument ...]
.SH DESCRIPTION
-This program sets or gets the io scheduling class and priority for a program.
+This program sets or gets the I/O scheduling class and priority for a program.
If no arguments or just \fB\-p\fR is given, \fBionice\fR will query the current
-io scheduling class and priority for that process.
+I/O scheduling class and priority for that process.
+
+When \fIcommand\fR is given,
+.B ionice
+will run this command with the given arguments.
+If no \fIclass\fR is specified, then
+.I command
+will be executed with the "best-effort" scheduling class. The default
+priority level is 4.
As of this writing, a process can be in one of three scheduling classes:
.IP "\fBIdle\fP"
-A program running with idle io priority will only get disk time when no other
-program has asked for disk io for a defined grace period. The impact of idle
-io processes on normal system activity should be zero. This scheduling
-class does not take a priority argument. Presently, this scheduling class
+A program running with idle I/O priority will only get disk time when no other
+program has asked for disk I/O for a defined grace period. The impact of an
+idle I/O process on normal system activity should be zero. This scheduling
+class does not take a priority argument. Presently, this scheduling class
is permitted for an ordinary user (since kernel 2.6.25).
-.IP "\fBBest effort\fP"
+.IP "\fBBest-effort\fP"
This is the effective scheduling class for any process that has not asked for
-a specific io priority.
-This class takes a priority argument from \fI0-7\fR, with lower
-number being higher priority. Programs running at the same best effort
+a specific I/O priority.
+This class takes a priority argument from \fI0-7\fR, with a lower
+number being higher priority. Programs running at the same best-effort
priority are served in a round-robin fashion.
-A process that has not asked for an io priority formally uses "\fBnone\fP" as
-scheduling class, but the io scheduler will treat such processes as if it
-were in the best effort class. The priority within the best effort class will
-be dynamically derived from the cpu nice level of the process: io_priority =
-(cpu_nice + 20) / 5.
-.IP "\fBReal time\fP"
+Note that before kernel 2.6.26 a process that has not asked for an I/O priority
+formally uses "\fBnone\fP" as scheduling class, but the I/O scheduler will treat
+such processes as if it were in the best-effort class. The priority within the
+best-effort class will be dynamically derived from the CPU nice level of the
+process: io_priority = (cpu_nice + 20) / 5.
+
+For kernels after 2.6.26 with the CFQ I/O scheduler, a process that has not asked
+for an I/O priority inherits its CPU scheduling class. The I/O priority is derived
+from the CPU nice level of the process (same as before kernel 2.6.26).
+
+.IP "\fBRealtime\fP"
The RT scheduling class is given first access to the disk, regardless of
-what else is going on in the system. Thus the RT class needs to be used with
-some care, as it can starve other processes. As with the best effort class,
+what else is going on in the system. Thus the RT class needs to be used with
+some care, as it can starve other processes. As with the best-effort class,
8 priority levels are defined denoting how big a time slice a given process
-will receive on each scheduling window. This scheduling class is not
+will receive on each scheduling window. This scheduling class is not
permitted for an ordinary (i.e., non-root) user.
.SH OPTIONS
-.IP "\fB-c \fIclass\fP"
-The scheduling class. \fI0\fR for none, \fI1\fR for real time, \fI2\fR for
-best-effort, \fI3\fR for idle.
-.IP "\fB-n \fIclassdata\fP"
-The scheduling class data. This defines the class data, if the class
-accepts an argument. For real time and best-effort, \fI0-7\fR is valid
-data.
-.IP "\fB-p \fIpid\fP"
-Pass in process PID(s) to view or change already running processes. If this argument
-is not given, \fBionice\fP will run the listed program with the given
-parameters.
-.IP "\fB-t\fP"
-Ignore failure to set requested priority. If COMMAND or PID(s) is specified, run it
-even in case it was not possible to set desired scheduling priority, what
-can happen due to insufficient privilegies or old kernel version.
+.TP
+.BR \-c , " \-\-class " \fIclass\fR
+Specify the name or number of the scheduling class to use; \fI0\fR for none,
+\fI1\fR for realtime, \fI2\fR for best-effort, \fI3\fR for idle.
+.TP
+.BR \-n , " \-\-classdata " \fIlevel\fR
+Specify the scheduling class data. This only has an effect if the class
+accepts an argument. For realtime and best-effort, \fI0-7\fR are valid data
+(priority levels).
+.TP
+.BR \-p , " \-\-pid " \fIPID\fR...
+Specify the process IDs of running processes for which to get or set the
+scheduling parameters.
+.TP
+.BR \-t , " \-\-ignore"
+Ignore failure to set the requested priority. If \fIcommand\fR was specified,
+run it even in case it was not possible to set the desired scheduling priority,
+which can happen due to insufficient privileges or an old kernel version.
+.TP
+.BR \-h , " \-\-help"
+Display help and exit.
+.TP
+.BR \-V , " \-\-version"
+Display version information and exit.
.SH EXAMPLES
.LP
.TP 7
# \fBionice\fP -c 3 -p 89
.TP 7
-Sets process with PID 89 as an idle io process.
+Sets process with PID 89 as an idle I/O process.
.TP 7
# \fBionice\fP -c 2 -n 0 bash
.TP 7
.TP 7
Prints the class and priority of the processes with PID 89 and 91.
.SH NOTES
-Linux supports io scheduling priorities and classes since 2.6.13 with the CFQ
-io scheduler.
+Linux supports I/O scheduling priorities and classes since 2.6.13 with the CFQ
+I/O scheduler.
.SH AUTHORS
+.nf
Jens Axboe <jens@axboe.dk>
+Karel Zak <kzak@redhat.com>
+.fi
.SH AVAILABILITY
-The ionice command is part of the util-linux-ng package and is available from
-ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
+The ionice command is part of the util-linux package and is available from
+ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
projects / framework / base / util-linux-ng.git / blobdiff