1IONICE(1)                        User Commands                       IONICE(1)
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NAME

6       ionice - set or get process I/O scheduling class and priority
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SYNOPSIS

9       ionice [-c class] [-n level] [-t] -p PID
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11       ionice [-c class] [-n level] [-t] -P PGID
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13       ionice [-c class] [-n level] [-t] -u UID
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15       ionice [-c class] [-n level] [-t] command [argument] ...
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DESCRIPTION

18       This program sets or gets the I/O scheduling class and priority for a
19       program. If no arguments or just -p is given, ionice will query the
20       current I/O scheduling class and priority for that process.
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22       When command is given, ionice will run this command with the given
23       arguments. If no class is specified, then command will be executed with
24       the "best-effort" scheduling class. The default priority level is 4.
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26       As of this writing, a process can be in one of three scheduling
27       classes:
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29       Idle
30           A program running with idle I/O priority will only get disk time
31           when no other program has asked for disk I/O for a defined grace
32           period. The impact of an idle I/O process on normal system activity
33           should be zero. This scheduling class does not take a priority
34           argument. Presently, this scheduling class is permitted for an
35           ordinary user (since kernel 2.6.25).
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37       Best-effort
38           This is the effective scheduling class for any process that has not
39           asked for a specific I/O priority. This class takes a priority
40           argument from 0-7, with a lower number being higher priority.
41           Programs running at the same best-effort priority are served in a
42           round-robin fashion.
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44           Note that before kernel 2.6.26 a process that has not asked for an
45           I/O priority formally uses "none" as scheduling class, but the I/O
46           scheduler will treat such processes as if it were in the
47           best-effort class. The priority within the best-effort class will
48           be dynamically derived from the CPU nice level of the process:
49           io_priority = (cpu_nice + 20) / 5.
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51           For kernels after 2.6.26 with the CFQ I/O scheduler, a process that
52           has not asked for an I/O priority inherits its CPU scheduling
53           class. The I/O priority is derived from the CPU nice level of the
54           process (same as before kernel 2.6.26).
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56       Realtime
57           The RT scheduling class is given first access to the disk,
58           regardless of what else is going on in the system. Thus the RT
59           class needs to be used with some care, as it can starve other
60           processes. As with the best-effort class, 8 priority levels are
61           defined denoting how big a time slice a given process will receive
62           on each scheduling window. This scheduling class is not permitted
63           for an ordinary (i.e., non-root) user.
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OPTIONS

66       -c, --class class
67           Specify the name or number of the scheduling class to use; 0 for
68           none, 1 for realtime, 2 for best-effort, 3 for idle.
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70       -n, --classdata level
71           Specify the scheduling class data. This only has an effect if the
72           class accepts an argument. For realtime and best-effort, 0-7 are
73           valid data (priority levels), and 0 represents the highest priority
74           level.
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76       -p, --pid PID...
77           Specify the process IDs of running processes for which to get or
78           set the scheduling parameters.
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80       -P, --pgid PGID...
81           Specify the process group IDs of running processes for which to get
82           or set the scheduling parameters.
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84       -t, --ignore
85           Ignore failure to set the requested priority. If command was
86           specified, run it even in case it was not possible to set the
87           desired scheduling priority, which can happen due to insufficient
88           privileges or an old kernel version.
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90       -u, --uid UID...
91           Specify the user IDs of running processes for which to get or set
92           the scheduling parameters.
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94       -h, --help
95           Display help text and exit.
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97       -V, --version
98           Print version and exit.
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NOTES

101       Linux supports I/O scheduling priorities and classes since 2.6.13 with
102       the CFQ I/O scheduler.
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EXAMPLES

105       •   # ionice -c 3 -p 89
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107       Sets process with PID 89 as an idle I/O process.
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109       •   # ionice -c 2 -n 0 bash
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111       Runs 'bash' as a best-effort program with highest priority.
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113       •   # ionice -p 89 91
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115       Prints the class and priority of the processes with PID 89 and 91.
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AUTHORS

118       Jens Axboe <jens@axboe.dk>, Karel Zak <kzak@redhat.com>
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SEE ALSO

121       ioprio_set(2)
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REPORTING BUGS

124       For bug reports, use the issue tracker at
125       https://github.com/util-linux/util-linux/issues.
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AVAILABILITY

128       The ionice command is part of the util-linux package which can be
129       downloaded from Linux Kernel Archive
130       <https://www.kernel.org/pub/linux/utils/util-linux/>.
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134util-linux 2.38                   2022-02-17                         IONICE(1)