Systemd, the system manager for Linux, is set to introduce a soft rebooting mode called “Systemctl Soft-Reboot” which only restarts user space components without affecting the Linux kernel. This new option is expected to reduce downtime during environment updates, particularly when using system images.
The new mode will finalize the operation of all processes in the user space and then replace the image of the root file system with a new version and initialize the system without rebooting the kernel. The ability to maintain a working kernel during the replacement of a user environment will enable Live mode updates of selected services with the transfer of file descriptors and listening network sockets from the old environment to the new one. This approach significantly reduces the replacement time of one system version with another while ensuring uninterrupted transfer of resources to important services.
The restart acceleration is made possible by removing relatively time-consuming stages such as equipment initialization, bootloader operation, kernel startup, driver initialization, firmware loading, and INITRD processing. The LivePatch mechanism will be used to update the kernel during mild rebooting without stopping the applications.
The new feature was announced by Lennart Pottering, and further details can be found in the Systemd Github Pull Request here.