Solved - See Update 2 below.
We have a Debian Jessie DNS / SSH server.
I have joined it to our AD domain by following this guide and created a cron job to sync the time with a domain controller using ntp. Additionally, I have put the AD group "sudoers" into /etc/sudoers with visudo.
This setup has worked just fine for a few months. Authorized domain users could log in with SSH and those who were members of the sudoers AD group could use sudo.
Suddenly domain users as well as root can no longer log in. Local user accounts except root still work. However, sudo no longer works.
When trying to log in as root or use su I get "No logon servers".
su -
Password:
No logon servers
su: authentification error
I am now stuck without root access. I can use sudo now - see update below.
Appending "single" and/or "init=/bin/bash" to the grub2 boot entry leaves me with an unresponsive shell:
Update: A PS/2 keyboard got the single user root shell working which allowed me to explicitly add my local user to the sudoers file. I now have root access in multi-user.
However, the login problem is still not fixed. Any ideas?
Update 2: DNS was incorrectly configured. Instead of querying itself (it is the primary domain DNS server) the server tried to get the DC address from 8.8.8.8... duh. Edited /etc/resolv.conf and everything magically works.
