Lennart Poettering shared insights on the preparation for adding a soft reboot mode to the system manager systemd ("systemctl soft-reboot"), which restarts only user space components without touching the Linux kernel. It is expected that, compared to a regular reboot, the soft reboot will reduce downtime during the updating of environments that use preconfigured system images.
The new mode will allow for terminating all processes in user space, after which the root filesystem image can be replaced with a new version and the system initialization process started without rebooting the kernel. Additionally, preserving the state of the running kernel during the replacement of the user environment will enable live updates for certain services, facilitating the transfer of file descriptors and listening network sockets for these services from the old environment to the new one. This will significantly reduce the time required to swap one system version for another and ensure seamless resource transfer to the most critical services that will continue to operate uninterrupted.
The acceleration of the reboot process is achieved by excluding relatively lengthy stages, such as hardware initialization, boot loader operation, kernel startup, driver initialization, firmware loading, and initrd processing. To update the kernel in conjunction with a soft reboot, the livepatch mechanism is proposed for applying fixes to the running Linux kernel without a complete reboot and without stopping applications.
Source: opennet.ru
