1IONICE(1) User Commands IONICE(1)
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6 ionice - set or get process I/O scheduling class and priority
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9 ionice [-c class] [-n level] [-t] -p PID...
10 ionice [-c class] [-n level] [-t] command [argument...]
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13 This program sets or gets the I/O scheduling class and priority for a
14 program. If no arguments or just -p is given, ionice will query the
15 current I/O scheduling class and priority for that process.
16 When command is given, ionice will run this command with the given
18 arguments. If no class is specified, then command will be executed
19 with the "best-effort" scheduling class. The default priority level is
20 4.
21 As of this writing, a process can be in one of three scheduling
23 classes:
24 Idle A program running with idle I/O priority will only get disk time
26 when no other program has asked for disk I/O for a defined grace
27 period. The impact of an idle I/O process on normal system
28 activity should be zero. This scheduling class does not take a
29 priority argument. Presently, this scheduling class is permit‐
30 ted for an ordinary user (since kernel 2.6.25).
31 Best-effort
33 This is the effective scheduling class for any process that has
34 not asked for a specific I/O priority. This class takes a pri‐
35 ority argument from 0-7, with a lower number being higher prior‐
36 ity. Programs running at the same best-effort priority are
37 served in a round-robin fashion.
38 Note that before kernel 2.6.26 a process that has not asked for
40 an I/O priority formally uses "none" as scheduling class, but
41 the I/O scheduler will treat such processes as if it were in the
42 best-effort class. The priority within the best-effort class
43 will be dynamically derived from the CPU nice level of the
44 process: io_priority = (cpu_nice + 20) / 5.
45 For kernels after 2.6.26 with the CFQ I/O scheduler, a process
47 that has not asked for an I/O priority inherits its CPU schedul‐
48 ing class. The I/O priority is derived from the CPU nice level
49 of the process (same as before kernel 2.6.26).
50 Realtime
53 The RT scheduling class is given first access to the disk,
54 regardless of what else is going on in the system. Thus the RT
55 class needs to be used with some care, as it can starve other
56 processes. As with the best-effort class, 8 priority levels are
57 defined denoting how big a time slice a given process will
58 receive on each scheduling window. This scheduling class is not
59 permitted for an ordinary (i.e., non-root) user.
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62 -c, --class class
63 Specify the name or number of the scheduling class to use; 0 for
64 none, 1 for realtime, 2 for best-effort, 3 for idle.
65 -n, --classdata level
67 Specify the scheduling class data. This only has an effect if
68 the class accepts an argument. For realtime and best-effort,
69 0-7 are valid data (priority levels).
70 -p, --pid PID...
72 Specify the process IDs of running processes for which to get or
73 set the scheduling parameters.
74 -t, --ignore
76 Ignore failure to set the requested priority. If command was
77 specified, run it even in case it was not possible to set the
78 desired scheduling priority, which can happen due to insuffi‐
79 cient privileges or an old kernel version.
80 -h, --help
82 Display help and exit.
83 -V, --version
85 Display version information and exit.
86
88 # ionice -c 3 -p 89
89 Sets process with PID 89 as an idle I/O process.
91 # ionice -c 2 -n 0 bash
93 Runs 'bash' as a best-effort program with highest priority.
95 # ionice -p 89 91
97 Prints the class and priority of the processes with PID 89 and 91.
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101 Linux supports I/O scheduling priorities and classes since 2.6.13 with
102 the CFQ I/O scheduler.
103
105 Jens Axboe <jens@axboe.dk>
106 Karel Zak <kzak@redhat.com>
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109 The ionice command is part of the util-linux package and is available
110 from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
111util-linux July 2011 IONICE(1)