Create a unit with an option longer than 2048 characters and attempt to start it. Check `systemctl status` and you are likely to see an error. The unit I used is a single ExecStart statement trying to echo 2018 periods:

[Service]
ExecStart=/bin/bash -c "echo ................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................."


And here are the logs:

Oct 21 23:54:53 core-01 systemd[1]: [/run/systemd/system/foo.service:3] Missing '='.
Oct 21 23:54:58 core-01 systemd[1]: [/run/systemd/system/foo.service:2] String is not UTF-8 clean, ignoring assignment: /bin/bash -c "echo ..................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................


Note that the error seems to be telling me I have a malformed option line, but it clearly chopped off the trailing double quote that would make it valid. I dug into this a bit, and it looks like shared/config-parser.c's config_parse uses LINE_MAX, which is defined as 2048 on my system. I tried googling around for any documentation of what the actual line limit is, and came up empty handed.

The ideal path forward here is to remove the line length limit. If that is unreasonable, this limit should at least be documented somewhere obvious. Additionally, the line length should be checked and logged, as the unrelated error I ran into ("String is not UTF-8 clean") is a red herring.