systemd is a set of system administration daemons, libraries, and tools designed as a central administration and configuration platform for interfacing with the Linux operating system kernel.
After five months of development, the launch of the new version of systemd 254, in which one of its main novelties is the compatibility with a soft restart mode, as well as a new utility to check the battery level, improvements, corrections and more.
In this new version of systemd 254 that is presented, as we already mentioned, one of its main novelties is the support for a soft reboot mode that causes only user space components to reboot without touching the Linux kernel. In the new mode, when rebooting, the stages of hardware initialization, bootloader call, kernel startup and loading, driver initialization, firmware loading and initrd processing are not applied, which allows to significantly speed up the reboot and reduce downtime when upgrading environments using out-of-the-box system images.
The new mode allows you to kill all processes in user space, then replace the FS root image with a new version and start the system boot process without rebooting the kernel.
Other changes that stand out in the new version is the systemd-battery-check utility to check battery level. The utility can be started at an early boot stage to prevent the system from starting with a very low battery level.
For service units, the settings are proposed MemoryPressureWatch and MemoryPressureThresholdSec, which allow to control the logic of use of the PSI subsystem (Pressure Stall Information) in connection with individual services. PSI provides information about the wait time for various resources to accurately assess the level of system load, allowing you to identify the beginning of delays due to lack of resources and selectively terminate intensive resources.
In addition to this, it is also highlighted thatand added the configuration RootEphemeral, which allows to use in the services where the parameters are set RootImage and RootDirectory, temporary copies of a disk image or directory tree, which are created via btrfs and reflink-y btrfs/xfs snapshots when the service starts, and are deleted after the service is stopped.
We can also find that added "fdstore" command to systemd-analyze utility to display the contents of the file descriptor store associated with a drive (used to restart stateless services; file descriptors are stored in fdstore before exit and restored on startup).
Moreover, for systemd-resolved, the StateRetentionSec parameter was added to resolve.conf, which allows DNS records to be cached longer specified via TTL and are used if the upstream DNS server stops responding. The "show-cache" command has been added to the resolvectl utility to view the contents of the DNS cache.
Of the other changes that stand out in this new version:
- Added the “–when” option to the reboot, kexec, shutdown, and stop commands in the systemctl utility to allow you to select when to reboot or stop.
- Added options “–fd” and “–fdname” to the systemd-notify utility to send arbitrary file descriptors to the service manager.
- Added “–exec” option to run the specified command after sending the message.
- Added the "systemctl list-paths" command to display all active path units, similar to the "systemctl list-timers" and "systemctl list-sockets" commands.
- Added the ability for units to set startup memory settings (Startup*, eg StartupMemoryMax), which is used similarly to startup CPU and I/O settings (StartupCPUWeight, etc.).
- The PID process automatically loads the virtio_console and virtio-vsock modules for virtual machines.
- For service units, added the DelegateSubgroup setting, which allows you to place services in existing subgroups instead of creating a separate parent cgroup for the service.
- Added the "whoami" command to the systemctl utility to display the name of the drive that the specified PID is associated with.
- Added '–list-cvm' option to systemd-detect-virt to list sensitive virtual machines.
- The kernel installation script has been rewritten in C.
Finally, if you are interested in knowing more about it, you can consult the details in the following link.