zram (previously called compcache) can create RAM based compressed block devices. It is a module of the Linux kernel since 3.2.

If physical swap devices exist, they will also be used by the system, but with a lower priority than a Zram device.

See Linux zram documentation and Zram for more info.

Similar results as with Zram can be achieved with Zswap, though Zswap needs a physical swap device (or swap file).

Automated setup

The packages zram-tools and systemd-zram-generator can be used to automatically setup zram devices.


zram-tools is available since Debian buster.

It currently only sets up zram devices on systemd-based systems.

To allow up to 60% of the RAM to be used as a zstd compressed swap space:

sudo apt install zram-tools
echo -e "ALGO=zstd\nPERCENT=60" | sudo tee -a /etc/default/zramswap
sudo service zramswap reload


zram-tools does not yet support sysvinit systems but there is an init script available. Download it and save it to /etc/init.d/zramswap, then make the script executable and then instruct your system to start it at boot time:

sudo chmod +x /etc/init.d/zramswap
sudo apt install insserv
sudo insserv zramswap


systemd-zram-generator integrates zram devices into systemd using generated swap (and ext2 mount) units. This allows managing them individually with systemctl when desired.

systemd-zram-generator comes with a default [zram0] section in /etc/systemd/zram-generator.conf. It defines a swap device which has 50% of available RAM or 4GiB, whichever is less.

Citing zram-generator's doc:

Manual setup

zramctl from util-linux can list the zram devices present and their status and control them.

$ sudo zramctl
/dev/zram0 lz4             4G  2.1G 248.6M 260.4M       8 [SWAP]