Manual: zramctl

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ZRAMCTL(8) System Administration ZRAMCTL(8)

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
nodes only when --find option specified. It’s possible (and common) that after system boot /dev/zram nodes are not
created yet.

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.

-h, --help
Display help text and exit.

-V, --version
Display version and exit.

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
Timofey Titovets , Karel Zak

Manual: zramctl

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