Bug 87249

Observed behavior:

[bob@a00:~]$ sudo systemctl enable /foo/bar.service
Failed to execute operation: Invalid argument

Expected behvaior:

[bob@a00:~]$ sudo systemctl enable /foo/bar.service
Unable to create symbolic link /etc/systemd/system/bar.service: target already exists

Details:

It seems that the systemd code generally passes error information as a single numeric code, even across contexts where the caller cannot know what the error code applies to.  This problem is further exacerbated by systemctl itself not doing any work; attempting to run systemctl under strace will not reveal additional context.

I would suggest making a per-thread error description string that takes precedence over errno if set, maybe something like this: https://gist.github.com/mortehu/df056c55958723b6836e