Ubuntu user hits thread number limit preventing SSH login
Recently I was investigating quite an interesting issue - there is Ubuntu based VM our testers run some tests on. It was reported they’re unable to log into the virtual machine.
After a brief investigation it became clear the issue is not network or SSH key related.
These are records from auth log:
/var/log/auth.log Feb 28 20:21:39 test-instance sshd: pam_unix(sshd:session): session opened for user ubuntu by (uid=0) Feb 28 20:21:39 test-instance systemd-logind: New session 75 of user ubuntu. Feb 28 20:21:39 test-instance sshd: fatal: fork of unprivileged child failed Feb 28 20:21:39 test-instance systemd-logind: Removed session 75.
Quite an obscure error message, but smells like cgroup problem. Indeed: