10-16-2008 01:00 AM
If you have ever found yourself in the position of having to reboot quickly or several times, you know that it's not a very quick process, particularly if you have SCSI devices or other initialization-intensive system devices. A package called kexec can speed up your reboots -- if you understand the rules.
Hello
Recently I found this (for me) really usefull tool kexec which can load a new Kernel while running one.
I tested it some times with the same kernel I was running, "rebooting" the system without powering it off at any time :D
But I need kexec basically just for live usbs. I want to start... (17 Replies)
SYSTEMD-HALT.SERVICE(8) systemd-halt.service SYSTEMD-HALT.SERVICE(8)NAME
systemd-halt.service, systemd-poweroff.service, systemd-reboot.service, systemd-kexec.service, systemd-shutdown - System shutdown logic
SYNOPSIS
systemd-halt.service
systemd-poweroff.service
systemd-reboot.service
systemd-kexec.service
/lib/systemd/systemd-shutdown
/lib/systemd/system-shutdown/
DESCRIPTION
systemd-halt.service is a system service that is pulled in by halt.target and is responsible for the actual system halt. Similarly,
systemd-poweroff.service is pulled in by poweroff.target, systemd-reboot.service by reboot.target and systemd-kexec.service by kexec.target
to execute the respective actions.
When these services are run, they ensure that PID 1 is replaced by the /lib/systemd/systemd-shutdown tool which is then responsible for the
actual shutdown. Before shutting down, this binary will try to unmount all remaining file systems, disable all remaining swap devices,
detach all remaining storage devices and kill all remaining processes.
It is necessary to have this code in a separate binary because otherwise rebooting after an upgrade might be broken -- the running PID 1
could still depend on libraries which are not available any more, thus keeping the file system busy, which then cannot be re-mounted
read-only.
Immediately before executing the actual system halt/poweroff/reboot/kexec systemd-shutdown will run all executables in
/lib/systemd/system-shutdown/ and pass one arguments to them: either "halt", "poweroff", "reboot" or "kexec", depending on the chosen
action. All executables in this directory are executed in parallel, and execution of the action is not continued before all executables
finished.
Note that systemd-halt.service (and the related units) should never be executed directly. Instead, trigger system shutdown with a command
such as "systemctl halt" or suchlike.
SEE ALSO systemd(1), systemctl(1), systemd.special(7), reboot(2), systemd-suspend.service(8)systemd 237SYSTEMD-HALT.SERVICE(8)