Wow, I finally had my first update problem with Ubuntu yesterday :-) After doing an update recently, all of a sudden I could no longer connect to my server. Port 22 was for some reason not reachable. Right away, I booted into a rescue system and went on checking the log files. At first I suspected there might be a problem with some fail2ban rules but everything appeared to be fine on that front.
Luckily, carrot-server’s support team had already someone with similar issues and pointed me at issue 634900 which describes a problem with the new ssh upstart config in OpenVZ containers. So after removing the “oom never” line from /etc/init/ssh.conf sshd finally started again.
But that was only the first problem. For some reason I couldn’t yet log in with anything other than my root account. Whenever I tried to connect with a different user I got this:
Cannot execute /bin/bash: Permission denied
Or a slight variation when using “su”:
Unable to cd to '/home/myusername'
Virtually every topic discussing a similar issue points at /bin having wrong permissions, but those were fine. What was wrong in my case was not /bin but / itself. So the fix was pretty simple:
chmod a+rx /
chmod a+rx /var
which was wrong too. No idea why, but finally I could log in again and restart all necessary services :-)