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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | FILES | EXAMPLE | AUTHORS | SEE ALSO | REPORTING BUGS | AVAILABILITY |
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ZRAMCTL(8) System Administration ZRAMCTL(8)
zramctl - set up and control zram devices
Get info:
zramctl [options]
Reset zram:
zramctl -r zramdev...
Print name of first unused zram device:
zramctl -f
Set up a zram device:
zramctl [-f | zramdev] [-s size] [-t number] [-a algorithm]
zramctl is used to quickly set up zram device parameters, to reset
zram devices, and to query the status of used zram devices.
If no option is given, all non-zero size zram devices are shown.
Note that zramdev node specified on command line has to already
exist. The command zramctl creates a new /dev/zram<N> nodes only
when --find option specified. It’s possible (and common) that
after system boot /dev/zram<N> nodes are not created yet.
-a, --algorithm lzo|lz4|lz4hc|deflate|842|zstd
Set the compression algorithm to be used for compressing data
in the zram device.
The list of supported algorithms could be inaccurate as it
depends on the current kernel configuration. A basic overview
can be obtained by using the command "cat
/sys/block/zram0/comp_algorithm"; however, please note that
this list might also be incomplete. This is due to the fact
that ZRAM utilizes the Crypto API, and if certain algorithms
were built as modules, it becomes impossible to enumerate all
of them.
-f, --find
Find the first unused zram device. If a --size argument is
present, then initialize the device.
-n, --noheadings
Do not print a header line in status output.
-o, --output list
Define the status output columns to be used. If no output
arrangement is specified, then a default set is used. Use
--help to get a list of all supported columns.
The default list of columns may be extended if list is
specified in the format +list (e.g., zramctl -o+COMP-RATIO).
--output-all
Output all available columns.
-p, --algorithm-params parameter...
Specify the parameters for the selected compression algorithm.
For example, level=9 dict=/etc/dictionary sets the compression
level and pre-trained dictionary. Parameters are
algorithm-specific.
-r, --reset zramdev...
Reset the specified zram device(s). The settings of a zram
device can be changed only after a reset.
--raw
Use the raw format for status output.
-s, --size size
Create a zram device of the specified size. Zram devices are
aligned to memory pages; when the requested size is not a
multiple of the page size, it will be rounded up to the next
multiple. When not otherwise specified, the unit of the size
parameter is bytes.
The size argument may be followed by the multiplicative
suffixes KiB (=1024), MiB (=1024*1024), and so on for GiB,
TiB, PiB, EiB, ZiB and YiB (the "iB" is optional, e.g., "K"
has the same meaning as "KiB") or the suffixes KB (=1000), MB
(=1000*1000), and so on for GB, TB, PB, EB, ZB and YB.
-t, --streams number
Set the maximum number of compression streams that can be used
for the device. The default is use all CPUs and one stream for
kernels older than 4.6.
-h, --help
Display help text and exit.
-V, --version
Display version and exit.
zramctl returns 0 on success, nonzero on failure.
/dev/zram[0..N]
zram block devices
The following commands set up a zram device with a size of one
gigabyte and use it as swap device.
# zramctl --find --size 1024M
/dev/zram0
# mkswap /dev/zram0
# swapon /dev/zram0
...
# swapoff /dev/zram0
# zramctl --reset /dev/zram0
Timofey Titovets <[email protected]>, Karel Zak
<[email protected]>
Linux kernel documentation
<https://docs.kernel.org/admin-guide/blockdev/zram.html>
For bug reports, use the issue tracker
<https://github.com/util-linux/util-linux/issues>.
The zramctl 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/>. 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 protected]. This page was obtained from the
project's upstream Git repository
⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
2025-08-11. (At that time, the date of the most recent commit that
was found in the repository was 2025-08-05.) 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 [email protected]
util-linux 2.42-start-521-ec46 2025-08-09 ZRAMCTL(8)
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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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