"systemctl kexec" reboots

[Alex Badea]

After the introduction of finalrd, "systemctl kexec" (with a kernel preloaded by "kexec -l ...") no longer kexec()s -- it reboots instead.

Can be reproduced for example using a livecd (say, xubuntu-18.04-desktop-amd64.iso):

sudo -i
apt-get update
apt-get install kexec-tools finalrd
systemctl start finalrd # optional
kexec -l /cdrom/casper/vmlinuz
systemctl kexec

Expected results: the system kexec's into the kernel and panics (due to lack of /init, since we haven't given it an initrd).

Actual results: the system reboots (e.g. the livecd's bootloader menu runs).

If we don't install "finalrd" above, kexec works normally.

[Alex Badea (vamposdecampos)]

Turns out, systemd's shutdown implementation fork/execs the kexec binary from kexec-tools; this is missing from the /run/initramfs finalrd. systemd then falls through to reboot: https://github.com/systemd/systemd/blob/a859abf062cef1511e4879c4ee39c6036ebeaec8/src/shutdown/shutdown.c#L557

One way to fix it might be for finalrd to "copy_exec /sbin/kexec" if it exists. Alternatively, the kexec-tools package might ship a finalrd hook instead.

[Dimitri John Ledkov (xnox)]

Yes, kexec-tools should ship finalrd hook to fix this.

[Launchpad Janitor (janitor)]

This bug was fixed in the package kexec-tools - 1:2.0.20-2.1ubuntu2

---------------
kexec-tools (1:2.0.20-2.1ubuntu2) groovy; urgency=medium

  * Add finalrd integration hook, to allow kexec with finalrd. LP:
    #1862300

 -- Dimitri John Ledkov <email address hidden> Thu, 10 Sep 2020 15:33:48 +0100