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
As of this writing, a process can be in one of three scheduling
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).
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).
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-
-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).
-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.
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.
Display help text and exit.
-u, --uid UID...
Specify the user IDs of running processes for which to get or
set the scheduling parameters.
Display version information and exit.
# 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.
This page is part of the util-linux (a random collection of Linux
utilities) project. Information about the project can be found at
⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have a
bug report for this manual page, send it to
email@example.com. This page was obtained from the
project's upstream Git repository
2015-01-22. If you discover any rendering problems in this HTML ver‐
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util-linux July 2011 IONICE(1)