[systemd-devel] Question about service dependency handling in systemd-228

[Uoti Urpala]

On Sat, 2017-11-25 at 12:08 +0700, Bao Nguyen wrote:
> [   41.154231] systemd[1]: nss-lookup.target: Dependency Before=nss-lookup.target dropped
> [   41.297229] systemd[1]: sockets.target: Found ordering cycle on sockets.target/start
> [   41.297236] systemd[1]: sockets.target: Found dependency on asi-My-5101.socket/start
> [   41.297239] systemd[1]: sockets.target: Found dependency on My-sshd.target/start
> [   41.297241] systemd[1]: sockets.target: Found dependency on My-syncd.service/start
> [   41.297244] systemd[1]: sockets.target: Found dependency on My-nfs-client.service/start
> [   41.297246] systemd[1]: sockets.target: Found dependency on My-handling.service/start


> My question is if there are any significant different about building tree dependency and handling cycle dependency between systemd-210 and systemd-228 that can lead to my current situation? I have checked the change log, source code but not found any useful info

Rather than start by trying to find differences between systemd
versions, I suggest you first find out exactly what goes wrong under
the newer systemd version. Exactly which dependency is wrong and
shouldn't be there? Where does that dependency come from? A system
where ordering dependencies form a cycle is not valid, so some
dependency explicitly listed in your unit files or implicitly added by
systemd must be wrong. After finding that out, you can then try to find
out what differs under the older systemd if it's still relevant.

In the above log, the most suspicious part is that it seems to say
"asi-My-5101.socket" depends on "My-sshd.target". A socket unit almost
certainly shouldn't have such dependencies, as normally a listening
socket can be opened regardless of the state of the rest of the system
(the main exception I can think of would be a UNIX socket at a
filesystem path that requires mounting something, but normally you
wouldn't do that...).


> And what does the message "nss-lookup.target: Dependency Before=nss-lookup.target dropped" mean? I do not see it in systemd-210.

Apparently the target had a dependency saying that it should be started
before itself, and such a blatantly impossible dependency was ignored.