Automatically start zram swap device on boot with systemd zram-generator under CentOS Stream 9

zram-generator package will install necessary tools to automate the creation on boot the compressed RAM devices. This article focuses on compressed swap devices.

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As of writing this article, the latest version in the package system under CentOS Stream 9 is 0.32. The the latest version on the original page of the software is much higher number 1.1.2 and many of the following configuration options are marked as OBSOLETE, but they work in the 0.32 version included in CentOS Stream 9 (and the new configuration options does not!). That’s why it is important to check the included sample configuration file.
The package installs no configuration file, just a sample configuration file – /usr/share/doc/zram-generator/zram-generator.conf.example.
zram in the kernel space –

STEP 1) Install the zram-generator

It is easy and straightforward, just a single package:

[root@srv) ~]# dnf install -y zram-generator
Last metadata expiration check: 3:42:20 ago on Fri 20 Oct 2023 05:18:32 AM UTC.
Dependencies resolved.
 Package                      Architecture         Version                      Repository               Size
 zram-generator               x86_64               0.3.2-7.el9                  appstream               409 k

Transaction Summary
Install  1 Package

Total download size: 409 k
Installed size: 983 k
Downloading Packages:
zram-generator-0.3.2-7.el9.x86_64.rpm                                         2.1 MB/s | 409 kB     00:00    
Total                                                                         1.3 MB/s | 409 kB     00:00     
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
  Preparing        :                                                                                      1/1 
  Installing       : zram-generator-0.3.2-7.el9.x86_64                                                    1/1 
  Running scriptlet: zram-generator-0.3.2-7.el9.x86_64                                                    1/1 
  Verifying        : zram-generator-0.3.2-7.el9.x86_64                                                    1/1 



STEP 2) Create a configuration and start the service

By default, there is no configuration file. The best place for it is /etc/systemd/zram-generator.conf.
Here is an example, which will fulfill the following:

  • Set the maximum RAM of the system, because it is a hard-coded 9G, by default. And if not redefined the device will be with 9G max memory no matter how much is tuned by the other options.
  • Set the RAM of the compressed device.
  • Set the fraction of the ram, which may be used by the device. Again as with the above configuration option, it is important, because it limits the maximum available memory to allocate for the compressed device.
  • Set the type of the device – filesystem or swap device.

There is the real world example configuration – /etc/systemd/zram-generator.conf

[root@srv ~]# cat /etc/systemd/zram-generator.conf
host-memory-limit = none
max-zram-size = 32768
zram-fraction = 1.0
compression-algorithm = zstd
swap-priority = 100
fs-type = swap

Keep on reading!