Ubuntu Manpage: zram-generator - Systemd unit generator for zram swap devices

Provided by: systemd-zram-generator_1.2.1-1_amd64

NAME

       zram-generator - Systemd unit generator for zram swap devices

SYNOPSIS

       /usr/lib/systemd/system-generators/zram-generator TARGET_DIR [2RGET_DIR 3RGET_DIR]
       /usr/lib/systemd/system-generators/zram-generator --setup-device DEVICE
       /usr/lib/systemd/system-generators/zram-generator --reset-device DEVICE

DESCRIPTION

zram-generator is a generator that creates systemd units to format and use compressed RAM
devices, either as swap or a file system.

The generator will be invoked by systemd early at boot. The generator will then:

1. read configuration files from {/etc,/lib}/systemd/zram-generator.conf[.d] (see
zram-generator.conf(5) for details);

2. generate systemd.swap(5) and/or systemd.mount(5) units into TARGET_DIR and connect
them to swap.target or local-fs.target as appropriate;

3. ensure the zram module is loaded and create the requested devices.

The generator does nothing if run inside a container (as determined by
systemd-detect-virt(8) --container).

The generator also understands the kernel command-line option systemd.zram. See
zram-generator.conf(5) for details.

Setting the ZRAM_GENERATOR_ROOT environment variable makes the generator run in test mode,
in which case containerisation is ignored and step 3 is skipped.
For the ramifications of ZRAM_GENERATOR_ROOT on config handling, see
zram-generator.conf(5).

Generated dev-zramN.swap units depend on systemd-zram-setup@zramN.service, which will:

1. read configuration files from {/etc,/lib}/systemd/zram-generator.conf[.d] (see
zram-generator.conf(5) for details);

2. set the desired compression algorithm, if any; if the current kernel doesn't
understand the specified algorithm, a warning is issued, but execution continues;

3. set the desired blockdev size and format it as swap with systemd-makefs(8).

Generated path-to-mount-point.mount units depend on systemd-zram-setup@zramN.service. The
effect is similar to what happens for swap units, but of course they are formatted with a
file system.

When the unit is stopped, the zram device is reset, freeing memory and allowing the device
to be reused.

zram-generator implements systemd.generator(7).

Applying config changes
This generator is invoked in early boot, and the devices it configures will be created
very early too, so the easiest way to apply config changes is to simply reboot the
machine.

Nevertheless, sometimes it may be useful to add new devices or apply config changes at
runtime. Applying new configuration means restarting the units, and that in turn means
recreating the zram devices. This means that file systems are temporarily unmounted and
their contents lost, and pages are moved out of the compressed swap device into other
memory. If this is acceptable, systemctl restart systemd-zram-setup@zramN or systemctl
restart systemd-zram-setup@* may be used to recreate a specific device or all configured
devices. (If the device didn't exist, restart will create it.) If the way the device is
used (e.g. the mount point or file system type) is changed, systemctl daemon-reload needs
to be called first to recreate systemd units. If a device or mount point is removed from
configuration, the unit should be stopped before calling daemon-reload. Otherwise, systemd
will not know how to stop the unit properly.

REPORTING BUGS

       https://github.com/systemd/zram-generator/issues

NAME

SYNOPSIS

DESCRIPTION

REPORTING BUGS

SEE ALSO