[systemd-devel] Ordering (apt) timer services to not run at the same time

[Julian Andres Klode]

Hi systemd folks,

(service and timer files being discussed at the bottom)

we are currently reworking the way automatic updates and upgrades work
on Ubuntu and Debian systems. We basically have two persistent timers
with associated services:

1. apt-daily - Downloads new lists and packages
2. apt-daily-upgrade - Performs upgrades

The first job should run spread out through the day (we run it twice
due to some other reasons), the latter in the morning between 6 and 7,
and at boot, daily-upgrade should be resumed after daily (so we added
After ordering relations to apt-daily-upgrade timer and service).

Now, we seem to be missing one bit: If daily-upgrade is already
running, and daily is about to start, daily should wait for
daily-upgrade to finish. I had hoped that maybe that works
automatically given that there is some ordering relation between the
two, but that did not work out. I tried adding Conflicts, but systemd
then said "loop to fast" and became unresponsive (not sure if caused
by this, but maybe).

Is there a way to make this work in systemd, or do we need to add
locking to the script invocation (like
s#ExecStart=#ExecStart=/usr/bin/flock /path/to/lock#)?

Here are the services and timers. Any help would be appreciated.

==> apt-daily.service <==
[Unit]
Description=Daily apt download activities
Documentation=man:apt(8)
ConditionACPower=true

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


==> apt-daily.timer <==
[Unit]
Description=Daily apt download activities
After=network-online.target
Wants=network-online.target

[Timer]
OnCalendar=*-*-* 6,18:00
RandomizedDelaySec=12h
Persistent=true

[Install]
WantedBy=timers.target

==> apt-daily-upgrade.service <==
[Unit]
Description=Daily apt upgrade and clean activities
Documentation=man:apt(8)
ConditionACPower=true
After=apt-daily.service

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

==> apt-daily-upgrade.timer <==
[Unit]
Description=Daily apt upgrade and clean activities
After=apt-daily.timer

[Timer]
OnCalendar=*-*-* 6:00
RandomizedDelaySec=60m
Persistent=true

[Install]
WantedBy=timers.target

-- 
Julian Andres Klode  - Debian Developer, Ubuntu Member

See http://wiki.debian.org/JulianAndresKlode and http://jak-linux.org/.