1 .TH ionice "1" "August 2005" ionice
3 ionice \- get/set program io scheduling class and priority
20 .IR COMMAND\ [ ARG ]...
22 This program sets or gets the io scheduling class and priority for a program.
23 If no arguments or just \fB\-p\fR is given, \fBionice\fR will query the current
24 io scheduling class and priority for that process.
26 As of this writing, a process can be in one of three scheduling classes:
28 A program running with idle io priority will only get disk time when no other
29 program has asked for disk io for a defined grace period. The impact of idle
30 io processes on normal system activity should be zero. This scheduling
31 class does not take a priority argument. Presently, this scheduling class
32 is permitted for an ordinary user (since kernel 2.6.25).
33 .IP "\fBBest effort\fP"
34 This is the effective scheduling class for any process that has not asked for
35 a specific io priority.
36 This class takes a priority argument from \fI0-7\fR, with lower
37 number being higher priority. Programs running at the same best effort
38 priority are served in a round-robin fashion.
40 A process that has not asked for an io priority formally uses "\fBnone\fP" as
41 scheduling class, but the io scheduler will treat such processes as if it
42 were in the best effort class. The priority within the best effort class will
43 be dynamically derived from the cpu nice level of the process: io_priority =
46 The RT scheduling class is given first access to the disk, regardless of
47 what else is going on in the system. Thus the RT class needs to be used with
48 some care, as it can starve other processes. As with the best effort class,
49 8 priority levels are defined denoting how big a time slice a given process
50 will receive on each scheduling window. This scheduling class is not
51 permitted for an ordinary (i.e., non-root) user.
53 .IP "\fB-c \fIclass\fP"
54 The scheduling class. \fI0\fR for none, \fI1\fR for real time, \fI2\fR for
55 best-effort, \fI3\fR for idle.
56 .IP "\fB-n \fIclassdata\fP"
57 The scheduling class data. This defines the class data, if the class
58 accepts an argument. For real time and best-effort, \fI0-7\fR is valid
61 Pass in process PID(s) to view or change already running processes. If this argument
62 is not given, \fBionice\fP will run the listed program with the given
65 Ignore failure to set requested priority. If COMMAND or PID(s) is specified, run it
66 even in case it was not possible to set desired scheduling priority, what
67 can happen due to insufficient privilegies or old kernel version.
71 # \fBionice\fP -c 3 -p 89
73 Sets process with PID 89 as an idle io process.
75 # \fBionice\fP -c 2 -n 0 bash
77 Runs 'bash' as a best-effort program with highest priority.
79 # \fBionice\fP -p 89 91
81 Prints the class and priority of the processes with PID 89 and 91.
83 Linux supports io scheduling priorities and classes since 2.6.13 with the CFQ
86 Jens Axboe <jens@axboe.dk>
88 The ionice command is part of the util-linux-ng package and is available from
89 ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.