ssh authentication on server not working without login

Question

linux

Good day!

I have a Linux machine with Ubuntu, which I go to via ssh. By the machine there are 2 users: 1st with the administrator's rights (master) and the second with limited (slave). Authentication takes place by keys, and now, recently, by a strange coincidence, the machine stopped letting me in as master, but without any problems it lets me in as slave. That being said, if I make #su master from a slave, then I can ssh into master again. Until I break the ssh slave session. For connection I use Putty.

Tell me, please, how to solve this, or at least in which direction to dig?

Answer 1

So, I finally overcame this case. gaelpa was right, ~/master was encrypted. But since I didn't do it myself, so I didn't know it. I found this by noticing the .ecryptfs folder in /home.
Another problem that I solved in the appendage: in my AuthorizedKeysFile ~/.ssh/authorized_keys config, which stopped working at some point, because this file began to be looked for in /home/root regardless of the user. For everything to work, you need to leave it as it was by default, i.e.: %h /.ssh/authorized_keys
Thanks to everyone who helped!

Answer 2

1. use verbose mode in ssh, for example, connect from a unix server or from ubunta itself to yourself (by logging in as a slave):
# ssh -v [email protected]
2. look at the logs in /var/log/ especially auth.log , security.log, messages.log
3. look at the contents of ~master/.ssh/ maybe there, besides the keys, some non-standard configs or rc-scripts.
4. look in /etc/ssh/, maybe you will find something in sshd_config or maybe there is an sshrc script there

Answer 3

the rights to ~master/.ssh and ~master/.ssh/authorized_keys
should be 700 and 600 respectively.

Answer 4

what is the “administrative”ness of master expressed in?
What groups are both of these users in?
sshd_config can you show?