zramctl(8) — Linux manual page


ZRAMCTL(8)                System Administration               ZRAMCTL(8)

NAME         top

       zramctl - set up and control zram devices

SYNOPSIS         top

       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         top

       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         top

       -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.

           Output all available columns.

           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
           Print version and exit.

EXIT STATUS         top

       zramctl returns 0 on success, nonzero on failure.

FILES         top

           zram block devices

EXAMPLE         top

       The following commands set up a zram device with a size of one
       gigabyte and use it as swap device.

            # zramctl --find --size 1024M
            # mkswap /dev/zram0
            # swapon /dev/zram0
            # swapoff /dev/zram0
            # zramctl --reset /dev/zram0

AUTHORS         top

       Timofey Titovets <nefelim4ag@gmail.com>, Karel Zak

SEE ALSO         top

       Linux kernel documentation

REPORTING BUGS         top

       For bug reports, use the issue tracker at

AVAILABILITY         top

       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
       util-linux@vger.kernel.org. This page was obtained from the
       project's upstream Git repository
       ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
       2024-06-14. (At that time, the date of the most recent commit
       that was found in the repository was 2024-06-10.) 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

util-linux 2.39.594-1e0ad      2023-08-25                     ZRAMCTL(8)