random_sleep is ignored on machines using systemd

[baldurmen]

Hi!

It seems that on Debian machines running systemd (at least on Debian Buster), the random_sleep parameter is ignored.

Indeed, apt transitioned from a cronjob to a systemd timer. /etc/cron.daily/apt-compat now starts with:

# Systemd systems use a systemd timer unit which is preferable to
# run. We want to randomize the apt update and unattended-upgrade
# runs as much as possible to avoid hitting the mirrors all at the
# same time. The systemd time is better at this than the fixed
# cron.daily time
if [ -d /run/systemd/system ]; then
    exit 0
fi

This means the cronjob exits if systemd is running. If that's the case, the machine uses /lib/systemd/system/apt-daily.timer instead to manage automated updates. On Buster, this file looks like:

[Unit]
Description=Daily apt download activities

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

[Install]
WantedBy=timers.target

It also seems RandomizedDelaySec is hard coded. I don't see a bug on apt for this issue, but I'll open one shortly.

To fix this issue, this module would need to modify the timer using the value passed to random_sleep and reload systemd daemons.

Cheers,