I normally ssh into my mailserver from another system with a GUI. This afternoon, I noticed the connection had closed, and when I tried to ssh back in I got a connection refused on Port 22 message.
So I had to plug in a keyboard and monitor and log directly onto the mail machine (Sarge setup). I eventually tried ssh restart and it still refused connections. So I poked thru the auth.log to find 'sshd FAILED daemon FATAL' and proceeded to Google that error message.
I came across a post from someone who found /dev/null had been changed into a regular file, and as soon as he repaired it and restarted ssh everything worked again.
Sure enough /dev/null was a regular file! A growing file. Also managed to Google
mknod -m 666 /dev/null c 1 3
as how to remake the /dev/null, but first I renamed the regular file null instead of deleting it.
The remake of /dev/null, a restart off ssh, and a successful log entry and all is well again.
What wrecked my /dev/null? Googling found odd problems like this from gcc, kconfig, and possibly webmin, none of which are running. Checking the renamed file I found this:
DCC -> check failed: Died at /usr/share/perl5/Mail/SpamAssassin/Dns.pm line 806.
Too late into the day to keep checking, but I will have to keep my eye on this. Just wondered if anyone has seen this problem? (googled already and found ONE but I don't read or speak German)