bootc-base-images/docs/usage.md

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Operating system content and usage

Configuring systemd units

To add a custom systemd unit:

COPY mycustom.service /usr/lib/systemd/system
RUN ln -s mycustom.service /usr/lib/systemd/system/default.target.wants

It will not work currently to do RUN systemctl enable mycustom.service instead of the second line - unless you also write a systemd preset file enabling that unit.

Static enablement versus presets

systemd presets are designed for "run once" semantics - thereafter, OS upgrades won't cause new services to start. In contrast, "static enablement" by creating the symlink (as is done above) bypasses the preset logic.

In general, it's recommended to follow the "static enablement" approach because it more closely aligns with "immutable infrastructure" model.

Using presets

If nevertheless you want to use presets instead of "static enablement", one recommended pattern to avoid this problem (and is also somewhat of a best practice anyways) is to use a common prefix (e.g. examplecorp- for all of your custom systemd units), resulting in examplecorp-checkin.service, examplecorp-agent.service etc.

Then you can write a single systemd preset file to e.g. /usr/lib/systemd/system-preset/50-examplecorp.preset that contains:

enable examplecorp-*

Automatic updates enabled by default

The base image here enables the bootc-fetch-apply-updates.service systemd unit which automatically finds updated container images from the registry and will reboot into them.

Controlling automatic updates

First, one can disable the timer entirely as part of a container build:

RUN systemctl mask bootc-fetch-apply-updates.timer

Alternatively, one can use systemd "drop-ins" to override the timer (for example, to schedule updates for once a week), create a file like this, named e.g. 50-weekly.conf:

[Timer]
# Clear previous timers
OnBootSec= OnBootSec=1w OnUnitInactiveSec=1w

Then add it into your container:

RUN mkdir -p /usr/lib/systemd/system/bootc-fetch-apply-updates.timer.d
COPY 50-weekly.conf /usr/lib/systemd/system/bootc-fetch-apply-updates.timer.d