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echo \
"[Unit]
Description=zenupdate.service

[Service]
Type=oneshot
ExecStart=/usr/bin/certbot -q renew --deploy-hook 'systemctl restart zend'
PrivateTmp=true" | sudo tee /lib/systemd/system/zenupdate.service

echo \
"[Unit]
Description=Run zenupdate unit daily @ 06:00:00 (UTC)

[Timer]
OnCalendar=*-*-* 06:00:00
Unit=zenupdate.service
Persistent=true

[Install]
WantedBy=timers.target" | sudo tee /lib/systemd/system/zenupdate.timer

sudo systemctl stop certbot.timer
sudo systemctl disable certbot.timer

sudo systemctl start zenupdate.service

sudo systemctl status zenupdate.service

zenops@node01:~$ sudo systemctl status zenupdate.service
● zenupdate.service
Loaded: loaded (/lib/systemd/system/zenupdate.service; static; vendor preset: enabled)
Active: inactive (dead) since Thu 2018-06-14 00:07:32 CEST; 19s ago

Jun 14 00:07:31 zsec01 systemd[1]: Starting zenupdate.service...
Jun 14 00:07:32 zsec01 systemd[1]: Started zenupdate.service.

sudo systemctl start zenupdate.timer
sudo systemctl enable zenupdate.timer

sudo systemctl status zenupdate.timer

zenops@node01:~$ sudo systemctl status zenupdate.timer
● zenupdate.timer - Run zenupdate unit daily @ 06:00:00 (UTC)
Loaded: loaded (/lib/systemd/system/zenupdate.timer; enabled; vendor preset: enabled)
Active: active (waiting) since Wed 2018-06-13 19:45:01 CEST; 4h 36min ago

Jun 13 19:45:01 node01 systemd[1]: Started Run zenupdate unit daily @ 06:00:00 (UTC).

sudo systemctl list-timers

zenops@node01:~$ sudo systemctl list-timers
NEXT.....................................................LEFT.......LAST..........................................................PASSED............................UNIT..........................................................ACTIVATES
Thu 2018-06-14 05:39:15 CEST 11h left..Wed 2018-06-13 08:12:43 CEST....9h ago.............................apt-daily.timer.......................................apt-daily.service
Thu 2018-06-14 06:00:00 CEST 12h left..n/a.............................................................n/a....................................zenupdate.timer...........................zenupdate.service
Thu 2018-06-14 06:18:28 CEST 12h left..Wed 2018-06-13 06:48:03 CEST....10h ago..........................apt-daily-upgrade.timer.....................apt-daily-upgrade.service
Thu 2018-06-14 17:32:10 CEST 23h left..Wed 2018-06-13 17:32:10 CEST....14min ago.....................systemd-tmpfiles-clean.timer..........systemd-tmpfiles-clean.service

4 timers listed.
Pass --all to see loaded but inactive timers, too.