swap-create@.service generator for zram devices

This generator provides a simple and fast mechanism to configure swap on /dev/zram* devices.

Create /etc/systemd/zram-generator.conf:

# /etc/systemd/zram-generator.conf
[zram0]
zram-fraction = 0.5

A zram device will be created for each section. No actual configuration is necessary (the default of zram-fraction=0.5 will be used unless overriden), but the configuration file with at least one section must exist.

A default config file may be located in /usr. This generator checks the following locations:

• /run/systemd/zram-generator.conf
• /etc/systemd/zram-generator.conf
• /usr/local/lib/systemd/zram-generator.conf
• /usr/lib/systemd/zram-generator.conf

… and the first file found in that list wins.

In addition, "drop-ins" will be loaded from .conf files in /etc/systemd/zram-generator.conf.d/, /usr/lib/systemd/zram-generator.conf.d/, etc.

The main configuration file is read before any of the drop-ins and has the lowest precedence; entries in the drop-in files override entries in the main configuration file.

See systemd.unit(5) for a detailed description of this logic.

See zram-generator.conf.example for a list of available settings.

The second purpose of this program is to serve as an example of a systemd generator in rust. Details are still being figured out.

Installation

Executing make install will create the following things:

• Generator binary installed as /usr/lib/systemd/system-generators/zram-generator
• zram-generator(8) and zram-generator.conf(5) manpages installed into /usr/share/man/manN/, this requires ronn.
• units/swap-create@.service copied into /usr/lib/systemd/system/
• zram-generator.conf.example copied into /usr/share/doc/zram-generator/ You need though create your own config file at one of the locations listed above.

Testing

The tests require either the zram module to be loaded, or root to run modprobe zram.

Set the ZRAM_GENERATOR_ROOT environment variable to use that instead of / as root.

The "{generator}" template in units/swap-create@.service.d/binary-location.conf can be substituted for a non-standard location of the binary for testing.

Authors

Written by Zbigniew Jędrzejewski-Szmek zbyszek@in.waw.pl, Igor Raits i.gnatenko.brain@gmail.com, наб nabijaczleweli@gmail.com, and others. See https://github.com/systemd/zram-generator/graphs/contributors for the full list.