systemd-logind since version 234 (released 2017-07-12) supports being
restarted without losing state [1]. From the systemd NEWS file [2]:
* systemd-logind may now be restarted without losing state. It stores
the file descriptors for devices it manages in the system manager
using the FDSTORE= mechanism. Please note that further changes in
other components may be required to make use of this (for example
Xorg has code to listen for stops of systemd-logind and terminate
itself when logind is stopped or restarted, in order to avoid using
stale file descriptors for graphical devices, which is now
counterproductive and must be reverted in order for restarts of
systemd-logind to be safe. See
https://cgit.freedesktop.org/xorg/xserver/commit/?id=dc48bd653c7e101.)
This reverts commit dc48bd653c.
Closes: #531
[1] https://github.com/systemd/systemd/pull/5600
[2] 9f09a95a7e
5a549c957a