Verified 1.1ubuntu1.18.04.8 on Bionic:

root@bb-lp-1806487-uu:~#  ln -s /dev/null /etc/systemd/system/systemd-logind.service
root@bb-lp-1806487-uu:~# service systemd-logind stop

root@bb-lp-1806487-uu:~# 
root@bb-lp-1806487-uu:~#  service systemd-logind status
● systemd-logind.service - Login Service
   Loaded: loaded (/lib/systemd/system/systemd-logind.service; masked; vendor preset: enabled)
   Active: inactive (dead) since Wed 2018-12-19 18:37:18 UTC; 4s ago
     Docs: man:systemd-logind.service(8)
           man:logind.conf(5)
           https://www.freedesktop.org/wiki/Software/systemd/logind
           https://www.freedesktop.org/wiki/Software/systemd/multiseat
  Process: 196 ExecStart=/lib/systemd/systemd-logind (code=killed, signal=TERM)
 Main PID: 196 (code=killed, signal=TERM)
   Status: "Processing requests..."

Dec 19 14:08:17 bb-lp-1806487-uu systemd[1]: Starting Login Service...
Dec 19 14:08:17 bb-lp-1806487-uu systemd-logind[196]: New seat seat0.
Dec 19 14:08:17 bb-lp-1806487-uu systemd[1]: Started Login Service.
Dec 19 18:35:38 bb-lp-1806487-uu systemd-logind[196]: New session c1 of user root.
Dec 19 18:36:17 bb-lp-1806487-uu systemd[1]: systemd-logind.service: Failed to reset devices.list: Operation not per
Dec 19 18:36:17 bb-lp-1806487-uu systemd[1]: systemd-logind.service: Failed to reset devices.list: Operation not per
Dec 19 18:36:18 bb-lp-1806487-uu systemd[1]: systemd-logind.service: Failed to reset devices.list: Operation not per
Dec 19 18:37:18 bb-lp-1806487-uu systemd[1]: Stopping Login Service...
Dec 19 18:37:18 bb-lp-1806487-uu systemd[1]: Stopped Login Service.
root@bb-lp-1806487-uu:~# systemctl daemon-reload
root@bb-lp-1806487-uu:~# service systemd-logind stop
root@bb-lp-1806487-uu:~# service systemd-logind status
● systemd-logind.service
   Loaded: masked (/dev/null; bad)
   Active: inactive (dead) since Wed 2018-12-19 18:37:18 UTC; 32s ago
 Main PID: 196 (code=killed, signal=TERM)
   Status: "Processing requests..."

Dec 19 14:08:17 bb-lp-1806487-uu systemd[1]: Starting Login Service...
Dec 19 14:08:17 bb-lp-1806487-uu systemd-logind[196]: New seat seat0.
Dec 19 14:08:17 bb-lp-1806487-uu systemd[1]: Started Login Service.
Dec 19 18:35:38 bb-lp-1806487-uu systemd-logind[196]: New session c1 of user root.
Dec 19 18:36:17 bb-lp-1806487-uu systemd[1]: systemd-logind.service: Failed to reset devices.list: Operation not per
Dec 19 18:36:17 bb-lp-1806487-uu systemd[1]: systemd-logind.service: Failed to reset devices.list: Operation not per
Dec 19 18:36:18 bb-lp-1806487-uu systemd[1]: systemd-logind.service: Failed to reset devices.list: Operation not per
Dec 19 18:37:18 bb-lp-1806487-uu systemd[1]: Stopping Login Service...
Dec 19 18:37:18 bb-lp-1806487-uu systemd[1]: Stopped Login Service.
root@bb-lp-1806487-uu:~# /usr/share/unattended-upgrades/unattended-upgrade-shutdown --debug
root@bb-lp-1806487-uu:~# tail /var/log/unattended-upgrades/unattended-upgrades-shutdown.log
2018-12-19 18:37:58,922 WARNING - Could not get delay inhibitor lock
2018-12-19 18:37:58,922 DEBUG - Skip waiting for signals, starting operation now
2018-12-19 18:37:58,923 DEBUG - Starting countdown of 25.0 minutes
2018-12-19 18:37:58,923 DEBUG - Initializing apt_pkg configuration
2018-12-19 18:37:58,923 DEBUG - get_lock returned 7
2018-12-19 18:37:58,923 DEBUG - lock not taken
root@bb-lp-1806487-uu:~# rm /etc/systemd/system/systemd-logind.service
root@bb-lp-1806487-uu:~# systemctl daemon-reload
root@bb-lp-1806487-uu:~#  service unattended-upgrades restart
root@bb-lp-1806487-uu:~# service unattended-upgrades status
● unattended-upgrades.service - Unattended Upgrades Shutdown
   Loaded: loaded (/lib/systemd/system/unattended-upgrades.service; enabled; vendor preset: enabled)
   Active: active (running) since Wed 2018-12-19 18:38:28 UTC; 4s ago
     Docs: man:unattended-upgrade(8)
 Main PID: 1149 (unattended-upgr)
    Tasks: 2 (limit: 4915)
   CGroup: /system.slice/unattended-upgrades.service
           └─1149 /usr/bin/python3 /usr/share/unattended-upgrades/unattended-upgrade-shutdown --wait-for-signal

Dec 19 18:38:28 bb-lp-1806487-uu systemd[1]: Started Unattended Upgrades Shutdown.
root@bb-lp-1806487-uu:~# tail /var/log/unattended-upgrades/unattended-upgrades-shutdown.log
2018-12-19 18:37:58,922 WARNING - Could not get delay inhibitor lock
2018-12-19 18:37:58,922 DEBUG - Skip waiting for signals, starting operation now
2018-12-19 18:37:58,923 DEBUG - Starting countdown of 25.0 minutes
2018-12-19 18:37:58,923 DEBUG - Initializing apt_pkg configuration
2018-12-19 18:37:58,923 DEBUG - get_lock returned 7
2018-12-19 18:37:58,923 DEBUG - lock not taken
2018-12-19 18:38:28,808 WARNING - SIGTERM or SIGHUP received, stopping unattended-upgradesonly if it is running
root@bb-lp-1806487-uu:~# service unattended-upgrades restart
root@bb-lp-1806487-uu:~# service unattended-upgrades status
● unattended-upgrades.service - Unattended Upgrades Shutdown
   Loaded: loaded (/lib/systemd/system/unattended-upgrades.service; enabled; vendor preset: enabled)
   Active: active (running) since Wed 2018-12-19 18:39:09 UTC; 2s ago
     Docs: man:unattended-upgrade(8)
 Main PID: 1163 (unattended-upgr)
    Tasks: 2 (limit: 4915)
   CGroup: /system.slice/unattended-upgrades.service
           └─1163 /usr/bin/python3 /usr/share/unattended-upgrades/unattended-upgrade-shutdown --wait-for-signal

Dec 19 18:39:09 bb-lp-1806487-uu systemd[1]: Started Unattended Upgrades Shutdown.
root@bb-lp-1806487-uu:~# tail /var/log/unattended-upgrades/unattended-upgrades-shutdown.logf
tail: cannot open '/var/log/unattended-upgrades/unattended-upgrades-shutdown.logf' for reading: No such file or directory
root@bb-lp-1806487-uu:~# tail /var/log/unattended-upgrades/unattended-upgrades-shutdown.log
2018-12-19 18:37:58,922 WARNING - Could not get delay inhibitor lock
2018-12-19 18:37:58,922 DEBUG - Skip waiting for signals, starting operation now
2018-12-19 18:37:58,923 DEBUG - Starting countdown of 25.0 minutes
2018-12-19 18:37:58,923 DEBUG - Initializing apt_pkg configuration
2018-12-19 18:37:58,923 DEBUG - get_lock returned 7
2018-12-19 18:37:58,923 DEBUG - lock not taken
2018-12-19 18:38:28,808 WARNING - SIGTERM or SIGHUP received, stopping unattended-upgradesonly if it is running
2018-12-19 18:39:09,702 WARNING - SIGTERM or SIGHUP received, stopping unattended-upgradesonly if it is running
root@bb-lp-1806487-uu:~# dpkg -l unattended-upgrades  | cat
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                Version            Architecture Description
+++-===================-==================-============-===========================================
ii  unattended-upgrades 1.1ubuntu1.18.04.8 all          automatic installation of security upgrades