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] -P PGID...
11 ionice [-c class] [-n level] [-t] -u UID...
12 ionice [-c class] [-n level] [-t] command [argument...]
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15 This program sets or gets the I/O scheduling class and priority for a
16 program. If no arguments or just -p is given, ionice will query the
17 current I/O scheduling class and priority for that process.
18 When command is given, ionice will run this command with the given
20 arguments. If no class is specified, then command will be executed
21 with the "best-effort" scheduling class. The default priority level is
22 4.
23 As of this writing, a process can be in one of three scheduling
25 classes:
26 Idle A program running with idle I/O priority will only get disk time
28 when no other program has asked for disk I/O for a defined grace
29 period. The impact of an idle I/O process on normal system
30 activity should be zero. This scheduling class does not take a
31 priority argument. Presently, this scheduling class is permit‐
32 ted for an ordinary user (since kernel 2.6.25).
33 Best-effort
35 This is the effective scheduling class for any process that has
36 not asked for a specific I/O priority. This class takes a pri‐
37 ority argument from 0-7, with a lower number being higher prior‐
38 ity. Programs running at the same best-effort priority are
39 served in a round-robin fashion.
40 Note that before kernel 2.6.26 a process that has not asked for
42 an I/O priority formally uses "none" as scheduling class, but
43 the I/O scheduler will treat such processes as if it were in the
44 best-effort class. The priority within the best-effort class
45 will be dynamically derived from the CPU nice level of the
46 process: io_priority = (cpu_nice + 20) / 5.
47 For kernels after 2.6.26 with the CFQ I/O scheduler, a process
49 that has not asked for an I/O priority inherits its CPU schedul‐
50 ing class. The I/O priority is derived from the CPU nice level
51 of the process (same as before kernel 2.6.26).
52 Realtime
55 The RT scheduling class is given first access to the disk,
56 regardless of what else is going on in the system. Thus the RT
57 class needs to be used with some care, as it can starve other
58 processes. As with the best-effort class, 8 priority levels are
59 defined denoting how big a time slice a given process will
60 receive on each scheduling window. This scheduling class is not
61 permitted for an ordinary (i.e., non-root) user.
62
64 -c, --class class
65 Specify the name or number of the scheduling class to use; 0 for
66 none, 1 for realtime, 2 for best-effort, 3 for idle.
67 -n, --classdata level
69 Specify the scheduling class data. This only has an effect if
70 the class accepts an argument. For realtime and best-effort,
71 0-7 are valid data (priority levels), and 0 represents the high‐
72 est priority level.
73 -p, --pid PID...
75 Specify the process IDs of running processes for which to get or
76 set the scheduling parameters.
77 -P, --pgid PGID...
79 Specify the process group IDs of running processes for which to
80 get or set the scheduling parameters.
81 -t, --ignore
83 Ignore failure to set the requested priority. If command was
84 specified, run it even in case it was not possible to set the
85 desired scheduling priority, which can happen due to insuffi‐
86 cient privileges or an old kernel version.
87 -h, --help
89 Display help text and exit.
90 -u, --uid UID...
92 Specify the user IDs of running processes for which to get or
93 set the scheduling parameters.
94 -V, --version
96 Display version information and exit.
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99 # ionice -c 3 -p 89
100 Sets process with PID 89 as an idle I/O process.
102 # ionice -c 2 -n 0 bash
104 Runs 'bash' as a best-effort program with highest priority.
106 # ionice -p 89 91
108 Prints the class and priority of the processes with PID 89 and 91.
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112 Linux supports I/O scheduling priorities and classes since 2.6.13 with
113 the CFQ I/O scheduler.
114
116 Jens Axboe <jens@axboe.dk>
117 Karel Zak <kzak@redhat.com>
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120 ioprio_set(2)
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123 The ionice command is part of the util-linux package and is available
124 from https://www.kernel.org/pub/linux/utils/util-linux/.
125util-linux July 2011 IONICE(1)