After updating two Ubuntu 16.04 servers with an update that did not include the kernel, but did include packages systemd and systemd-sysv, I checked the following file:
ls -la /var/run/reboot-required
It was not present on one server but was present on the other. Not expecting this discrepancy, I did not check for the file prior to the updates. While I cannot rule out that the file may have already been there on the one server, that is unlikely as the server was rebooted two weeks ago after a kernel update and that was the last time any updates were done.
Is there a more reliable way to know which packages require a reboot and/or when the server needs to be rebooted, especially on distros like Arch?
As a general rule, do I need to reboot when upgrading systemd?
In case it helps, for upgrading ubuntu, I use this command:
apt-get update && apt-get dist-upgrade
For upgrading Arch, I follow a few more steps, but the basic command is simply:
pacman -Syu pacman -Qtdq