I did some upgrades of what seemed like a million packages today on my Debian sid computer. I was doing this remotely and when I tried to ssh back in I got kicked out after entering my password, hmmm.
OK, so I waited until I could get in front of it and tried to login to the console and was greeted with the message “Cannot make/remove an entry” and kicked out, even as root; double hmmm.
So it was boot into single user time which, thankfully worked. bash loaded ok so it wasn’t a shell problem. However su failed which means we are into pam problem territory. I found a bug report that sounded like my problem, but with no clear solution except upgrade in Ubuntu.
The solution was pretty simple for me. It’s something funky with /etc/pam.d/common-sesssion and a simple ‘/usr/sbin/pam-auth-update’ fixed it for me.