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]
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).
- -p, --pid PID...
- Specify the process 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.
- -h, --help
- Display help and exit.
- -V, --version
- Display version information and exit.
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.
NOTES¶
Linux supports I/O scheduling priorities and classes since 2.6.13 with the CFQ
I/O scheduler.
AUTHORS¶
Jens Axboe <jens@axboe.dk>
Karel Zak <kzak@redhat.com>
AVAILABILITY¶
The ionice command is part of the util-linux package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux/.