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NAME | SYNOPSIS | DESCRIPTION | CONFIGURATION DIRECTORIES AND PRECEDENCE | OPTIONS | SEE ALSO | NOTES | COLOPHON |
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IOCOST.CONF(5) iocost.conf IOCOST.CONF(5)
iocost.conf - Configuration files for the iocost solution manager
/etc/systemd/iocost.conf /etc/systemd/iocost.conf.d/*.conf
This file configures the behavior of "iocost", a tool mostly used
by systemd-udevd(8) rules to automatically apply I/O cost
solutions to /sys/fs/cgroup/io.cost.*.
The qos and model values are calculated based on benchmarks
collected on the iocost-benchmark[1] project and turned into a set
of solutions that go from most to least isolated. Isolation allows
the system to remain responsive in face of high I/O load. Which
solutions are available for a device can be queried from the udev
metadata attached to it. By default the naive solution is used,
which provides the most bandwidth.
The default configuration is set during compilation, so
configuration is only needed when it is necessary to deviate from
those defaults. The main configuration file is loaded from one of
the listed directories in order of priority, only the first file
found is used: /etc/systemd/, /run/systemd/,
/usr/local/lib/systemd/ [2], /usr/lib/systemd/. The vendor version
of the file contains commented out entries showing the defaults as
a guide to the administrator. Local overrides can also be created
by creating drop-ins, as described below. The main configuration
file can also be edited for this purpose (or a copy in /etc/ if it
is shipped under /usr/), however using drop-ins for local
configuration is recommended over modifications to the main
configuration file.
In addition to the main configuration file, drop-in configuration
snippets are read from /usr/lib/systemd/*.conf.d/,
/usr/local/lib/systemd/*.conf.d/, and /etc/systemd/*.conf.d/.
Those drop-ins have higher precedence and override the main
configuration file. Files in the *.conf.d/ configuration
subdirectories are sorted by their filename in lexicographic
order, regardless of in which of the subdirectories they reside.
When multiple files specify the same option, for options which
accept just a single value, the entry in the file sorted last
takes precedence, and for options which accept a list of values,
entries are collected as they occur in the sorted files.
When packages need to customize the configuration, they can
install drop-ins under /usr/. Files in /etc/ are reserved for the
local administrator, who may use this logic to override the
configuration files installed by vendor packages. Drop-ins have to
be used to override package drop-ins, since the main configuration
file has lower precedence. It is recommended to prefix all
filenames in those subdirectories with a two-digit number and a
dash, to simplify the ordering. This also defines a concept of
drop-in priorities to allow OS vendors to ship drop-ins within a
specific range lower than the range used by users. This should
lower the risk of package drop-ins overriding accidentally
drop-ins defined by users. It is recommended to use the range
10-40 for drop-ins in /usr/ and the range 60-90 for drop-ins in
/etc/ and /run/, to make sure that local and transient drop-ins
take priority over drop-ins shipped by the OS vendor.
To disable a configuration file supplied by the vendor, the
recommended way is to place a symlink to /dev/null in the
configuration directory in /etc/, with the same filename as the
vendor configuration file.
All options are configured in the [IOCost] section:
TargetSolution=
Chooses which I/O cost solution (identified by named string)
should be used for the devices in this system. The known
solutions can be queried from the udev metadata attached to
the devices. If a device does not have the specified solution,
the first one listed in IOCOST_SOLUTIONS is used instead.
E.g. "TargetSolution=isolated-bandwidth".
Added in version 254.
udevadm(8), The iocost-benchmarks github project[1], The
resctl-bench documentation details how the values are obtained[3]
1. iocost-benchmark
https://github.com/iocost-benchmark/iocost-benchmarks
2. 💣💥🧨💥💥💣 Please note that those configuration files must
be available at all times. If /usr/local/ is a separate
partition, it may not be available during early boot, and must
not be used for configuration.
3. The resctl-bench documentation details how the values are
obtained
https://github.com/facebookexperimental/resctl-demo/tree/main/resctl-bench/doc
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 IOCOST.CONF(5)
Pages that refer to this page: systemd.directives(7), systemd.index(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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