scheduling a shutdown; wait a short while ; restart systemd-logind; cancel
shutdown; /run/nologin is not removed; login is not possible; after time of
planned shutdown is exceeded, even root access per ssh (if configured) is not
possible anymore!

leap1:~ # shutdown -r +5 ;
Shutdown scheduled for Sun 2021-07-04 18:36:59 CEST, use 'shutdown -c' to
cancel.
leap1:~ # ls -l /run/nologin
-rw-r--r-- 1 root root 22 Jul 4 18:32 /run/nologin
leap1:~ # systemctl restart systemd-logind ;
leap1:~ # shutdown -c ;
leap1:~ # ls -l /run/nologin
-rw-r--r-- 1 root root 22 Jul 4 18:32 /run/nologin
leap1:~ # more /run/nologin
System is going down.

no login possible anymore becaus of /run/nologin