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.

Use --help to get an overview of the supported output columns and their descriptions.

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.

-b, --bytes
    Print sizes in bytes, not in human-readable format.

-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.

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

SEE ALSO

REPORTING BUGS

For bug reports, use the

AVAILABILITY

The zramctl command is part of the util-linux package which can be downloaded from