[systemd-devel] Creating a man page with 'recipes' for common unit dependency combinations

Fri May 26 01:07:06 UTC 2023

As I use systemd more and more I find myself needing to express complex dependencies between units. While systemd provides many 'building blocks' which can be combined to satisfy the requirements, determining which blocks to use, and the pros/cons of each combination, is non-trivial.

Attempting to find examples using search engines generally leads to Stack Overflow posts with no answers, or with answers which are wildly out of date, or are just incorrect.

I'd like to create a man page to be included with all the rest of the systemd man pages which details relatively common scenarios, and the various ways that each can be achieved using the dependency options available.

For example, right now I've got a situation with two service units, A and B. I want B to always be started when A is started, stopped when A is stopped, stopped if A stops itself, restarted if A is restarted, but otherwise left alone (so it should not be 'upheld' by A). I suspect this is not an uncommon combination, and it would be useful to be able to document one (or more) ways that unit dependency specifications can be used achieve this goal.

If this was contained in a man page in the systemd tree, it could then be updated as new versions are released with changes in dependency behavior, and improved when new versions offer additional dependency specifications as well. It would also be available on the freedesktop.org site with the rest of the man pages, and over time might end up being the place that most searches land.

Is this something that would be welcomed by the systemd team? Are there others out there listening who would be willing to help build this (contributing use cases, or reviewing/testing proposed solutions)? I'm happy to drive this effort, if so.
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