systemd 254 With New Soft Reboots Feature, systemd-battery-check

Systemd 254 is out today in time for appearing in the late-2023 Linux distribution releases.

Systemd 254 is a big feature release over systemd 253 from February. Among the many changes to find with systemd 254 include:

- A new "soft-reboot" mechanism has been added to the systemd service manager. A soft reboot is similar to a regular reboot but that it affects user-space only. Initiating a systemd soft reboot will shutdown any running services and other units and then optionally switch to any new root file-system and then bring back up all the user-space services without rebooting the kernel.

- Startup memory settings are now supported.

- systemctl list-paths is now an option top show all currently active .path units.

- PID 1 will automatically load the virtio_console kernel module during early initialization if running in a relevant virtual machine. The virtio-vsock module will also be similarly loaded where relevant.

- The systemctl clean command can be used to clear the FDSTORE of a service.

- A new "MemoryKSM" service setting to enable kernel same-page merging individually for services.

- systemd-stub now allows optionally loading UEFI PE add-on images that may contain additional kernel command-line information. Ukify has also been extended to allow building UEFI PE add-on images.

- The systemd kernel-install script has been rewritten in C.

- Service units gained MemoryPressureWatch= and MemoryPressureThresholdSec= options to configure the PSI memory pressure logic individually.

- A new "systemd-battery-check" command that is run during the early boot phase and checks the battery level of the system if available. This is used to warn the user then via the Plymouth splash screen integration for example if the battery level is very low and to then turn off the system after a 10 second delay.

Downloads and the full list of systemd 254 changes via GitHub.