systemd-tmpfiles won't start

I had exactly the same problem today on my workstation - ubuntu 18.04.1. Finally (searching systemd source code) I have figured, that somehow my root folder = / ownership had been changed to me - the only user. Simple chown root.root / solved the problem :) ... after some 2 hours of searching.

$ cd /

$ ll (here if you see that ./ has any name other than root, then do)

$ sudo chown root.root /

you should see a normal prompt without a message. Now if you did:

$ sudo apt remove (the package in question) - then do

$ sudo apt install (that same package or tool above).

That error should go away and everything should be fine now.

Encountered this problem as well.

To add to the answer above, you need to make sure that the whole path belongs to root, not just /. Somehow my /var folder got the owner of mysql (good job, mysql), and sshd was trying to create /var/run/sshd, which failed.