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).
- -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.
- -h, --help
- Display help text and exit.
- -u, --uid UID...
- Specify the user IDs of running processes for which to get or set the
scheduling parameters.
- -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/.