systemd starting service even if service in requires wont start

Question

I have a test systemd service that I am testing. I have test.service which looks like this

[Unit]
Description=Dovid Demo Service
After=mariadb.service
Requires=mariadb.service

[Service]
ExecStart=/home/dovid/test.sh
User=dovid
Group=dovid

[Install]
WantedBy=default.target

If I do

systemctl start test

It will first start MariaDB and then start my script. However if I have MariaDB masked (I did systemctl mask mariadb) then MariaDB wont start yet systemd will start up test.sh. Shouldn't it fail because start a required process which in this case is MariaDB?

Answer 1

This is a bug in systemd. I have filed a bug report and done analysis of what is wrong here: https://github.com/systemd/systemd/issues/11338

That issue manifests here as the target gains a Wants= on the unit that Requires= a masked unit. The transaction is built and systemd has already added a job for the anchor unit, its Wants= dependency, and does not remove it when it gets -ERFKILL in your case, and propagating this up to the function called for UNIT_WANTS ignores it (as it isn't a fatal error), so you end up having the unit started even when required unit is masked.

This happens with many other cases, like RequiresMountsFor= for non-existent paths, etc. Same for BindsTo= as well.

Doing traversal from the bottom up is something I played around with, but that results in another issue: if some unit Requires=existing.service non-existent.service, it will still queue a spurious job, so this adding of jobs needs to be atomic at some level. Moreover, it may not enqueue a spurious job, depending on the order you specify things in.

Anyway, consider bumping that GitHub issue, and explain how you're hitting it.