zramctl

set up and control zram devices

TLDR

Check if zram is enabled

$ lsmod | grep -i zram

Enable zram with a dynamic number of devices (use zramctl to configure devices further)

$ sudo modprobe zram

Enable zram with exactly 2 devices

$ sudo modprobe zram num_devices=[2]

Find and initialize the next free zram device to a 2 GB virtual drive using LZ4 compression

$ sudo zramctl --find --size [2GB] --algorithm [lz4]

List currently initialized devices

$ zramctl

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

Set the compression algorithm to be used for compressing data in the zram device.

-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

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

Print 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

REPORTING BUGS

For bug reports, use the issue tracker at <https://github.com/util-linux/util-linux/issues>.

AVAILABILITY

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/>.