//po4a: entry man manual
= zramctl(8)
:doctype: manpage
:man manual: System Administration
:man source: util-linux {release-version}
:page-layout: base
:command: zramctl

== NAME

zramctl - set up and control zram devices

== SYNOPSIS

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_]

== DESCRIPTION

*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.

== OPTIONS

*-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*).

*-p*, *--algorithm-params*::
Set the algorithm parameters, for example, *level=9 dict=/etc/dictionary* to set compression level and pre-trained dictionary. Parameters are algorithm specific.

*--output-all*::
Output all available columns.

*--raw*::
Use the raw format for status output.

*-r*, *--reset*::
Reset the options of the specified zram device(s). Zram device settings can be changed only after a reset.

*-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.

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== EXIT STATUS

*zramctl* returns 0 on success, nonzero on failure.

== FILES

_/dev/zram[0..N]_::
zram block devices

== EXAMPLE

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
....

== AUTHORS

mailto:nefelim4ag@gmail.com[Timofey Titovets],
mailto:kzak@redhat.com[Karel Zak]

== SEE ALSO

link:https://docs.kernel.org/admin-guide/blockdev/zram.html[Linux kernel documentation]

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