IONICE(1) User Commands IONICE(1)
NAME
ionice - set or get process I/O scheduling class and priority
SYNOPSIS
ionice [-c class] [-n level] [-t] -p PID
ionice [-c class] [-n level] [-t] -P PGID
ionice [-c class] [-n level] [-t] -u UID
ionice [-c class] [-n level] [-t] command [argument] ...
DESCRIPTION
This program sets or gets the I/O scheduling class and priority for a
program. If no arguments or just -p is given, ionice will query the
current I/O scheduling class and priority for that process.
When command is given, ionice will run this command with the given
arguments. If no class is specified, then 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:
Idle
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).
Best-effort
This is the effective scheduling class for any process that has not
asked for a specific I/O priority. This class takes a priority
argument from 0-7, with a lower number being higher priority.
Programs running at the same best-effort priority are served in a
round-robin fashion.
Note that before kernel 2.6.26 a process that has not asked for an
I/O priority formally uses "none" 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).
Realtime
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, 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 permitted
for an ordinary (i.e., non-root) user.
OPTIONS
-c, --class class
Specify the name or number of the scheduling class to use; 0 for
none, 1 for realtime, 2 for best-effort, 3 for idle.
-n, --classdata level
Specify the scheduling class data. This only has an effect if the
class accepts an argument. For realtime and best-effort, 0-7 are
valid data (priority levels), and 0 represents the highest priority
level.
-p, --pid PID...
Specify the process IDs of running processes for which to get or
set the scheduling parameters.
-P, --pgid PGID...
Specify the process group IDs of running processes for which to get
or set the scheduling parameters.
-t, --ignore
Ignore failure to set the requested priority. If command 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.
-u, --uid UID...
Specify the user IDs of running processes for which to get or set
the scheduling parameters.
-h, --help
Display help text and exit.
-V, --version
Print version and exit.
NOTES
Linux supports I/O scheduling priorities and classes since 2.6.13 with
the CFQ I/O scheduler.
EXAMPLES
• # ionice -c 3 -p 89
Sets process with PID 89 as an idle I/O process.
• # ionice -c 2 -n 0 bash
Runs 'bash' as a best-effort program with highest priority.
• # ionice -p 89 91
Prints the class and priority of the processes with PID 89 and 91.
AUTHORS
Jens Axboe <jens@axboe.dk>, Karel Zak <kzak@redhat.com>
SEE ALSO
ioprio_set(2)
REPORTING BUGS
For bug reports, use the issue tracker at
https://github.com/util-linux/util-linux/issues.
AVAILABILITY
The ionice command is part of the util-linux package which can be
downloaded from Linux Kernel Archive
<https://www.kernel.org/pub/linux/utils/util-linux/>.
util-linux 2.38.1 2022-05-11 IONICE(1)
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