Hi list, I was recently pondering how systemd could use kexec "properly", in a reasonably general way, to make reboots faster. I exchanged an email with Poettering on the systemd list and he suggested me to ask here. My current proposal: 1. Include a template 'kexec-load.service' with kexec-tools, which distros/users could customize to load the right kernel and initrd via /sbin/kexec 2. If the user does 'systemctl enable kexec-load.service', then this service would trigger before every reboot. Loading the kernel any earlier would waste memory (5+14 MB on Ubuntu Server). Also a common reason for rebooting is to boot into a newly-installed kernel. Loading it any earlier would boot you into an older kernel. 3. During a reboot, after systemd has finished shutting down, it detects via /sys/kernel/kexec_loaded whether the kexec kernel is loaded. If 1, it performs a 'kexec -e'. If not, it does a normal reboot. ---- Lennart commented on #2 that kexec might have problems finding contiguous memory to load the kernel into, this late in the lifecycle. Do you think this is a deal-breaker for such a feature? If it's rare enough, then it might not be a problem -- we can always fall back to a normal reboot. I'm also assuming that "kexec --load" will fail atomically -- that it won't try to boot a half-loaded kernel, or boot a kernel whose initrd failed to load. Also, #3 doesn't yet work that way in systemd (currently it detects before shutdown) and Poettering hasn't agreed yet. Does this proposal seem sane to kexec folks? Did I miss anything? ---- Here are my and Poettering's initial thoughts on this matter: http://lists.freedesktop.org/archives/systemd-devel/2012-March/004760.html http://lists.freedesktop.org/archives/systemd-devel/2012-March/004764.html PS: I hope I haven't broken any rules by cross-posting this. This question seems relevant to both projects. Regards, Marti
