Systemd: how to start a service after another, started by timer, finishes

debian-stretchsystemd

The goal

On Debian Stretch, we want to download any updates and install them immediately because we monitor the number of pending upgrades and currently get notifications for routine conditions.

Standard stretch

Standard stretch downloads updates and installs them using:

  • apt-daily.service
  • apt-daily.timer
  • apt-daily-upgrade.service
  • apt-daily-upgrade.timer

The timers run independently at random daily times so there can be almost 24 hours between download and installation.

Research and attempts

apt-daily-upgrade.service modification

Based on https://superuser.com/questions/1250874/trigger-another-systemd-unit-to-start-before-timer-unit-starts, I disabled apt-daily-upgrade.timer and modified apt-daily-upgrade.service, adding "Wants=apt-daily.service"

Did run systemctl daemon-reload after the change.

24+ hours later /var/log/unattended-upgrades/unattended-upgrades.log did not show unattended-upgrades had been run.

apt-daily.service modification

Based on Chaining custom systemd services, I understood apt-daily.service needs to be configured to start apt-daily-upgrade.service rather than apt-daily-upgrade.service being configured to start after apt-daily.service.

Backed out the apt-daily-upgrade.service modification and created /etc/systemd/system/apt-daily.service with addition "Before=apt-daily-upgrade.service": 

[Unit]
Description=Daily apt download activities
Documentation=man:apt(8)
ConditionACPower=true
After=network-online.target
Wants=network-online.target
Before=apt-daily-upgrade.service

[Service]
Type=oneshot
ExecStart=/usr/lib/apt/apt.systemd.daily update

Did run systemctl daemon-reload after the change.

24+ hours later /var/log/unattended-upgrades/unattended-upgrades.log did not show unattended-upgrades had been run.

The systemd journal showed "Daily apt download activities" messages, believed to show that apt-daily.service had been run:

# journalctl | grep 'apt download activities'
Apr 08 16:10:05 web2.iciti.av systemd[1]: Starting Daily apt download activities...
Apr 08 16:10:08 web2.iciti.av systemd[1]: Started Daily apt download activities.
...

Conclusion

How can we effect our goal, ideally within the systemd framework?

Best Answer

Thanks user228505, that worked.

/etc/systemd/system/apt-daily.service was changed to

[Unit]
Description=Daily apt download activities
Documentation=man:apt(8)
ConditionACPower=true
After=network-online.target
Wants=network-online.target
Before=apt-daily-upgrade.service
Wants=apt-daily-upgrade.service

[Service]
Type=oneshot
ExecStart=/usr/lib/apt/apt.systemd.daily update

We needed that to run apt-daily-upgrade.service after apt-daily.service had finished (to download all packages before running unattended upgrades).

Adding APT::Periodic::Verbose "3" to /etc/apt/apt.conf.d/02periodic showed it was doing what we wanted.

Apparently the systemd message "Started Daily apt download activities" means "Finished Daily apt download activities" because /usr/lib/apt/apt.systemd.daily does not return until it has finished (unlike most service commands which return when they daemonize).

Related Topic