Kerberos and ssh

So you're setting up Kerberos and you've got a ticket with kinit

the target has a host/@REALM

but ssh fails with:

debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context

Well the first thing to realise is that you're probably not using gssapi-keyex, you're probably using gssapi-with-mic (see http://www.ietf.org/rfc/rfc4462.txt if you want to know more).

Running:

/usr/bin/sshd -D -ddd -e

may give

debug2: input_userauth_request: try method gssapi-with-mic
debug3: mm_request_send entering: type 38
debug3: mm_request_receive_expect entering: type 39
debug3: mm_request_receive entering
debug3: monitor_read: checking request 38
debug1: Unspecified GSS failure.  Minor code may provide more information
Key table entry not found

The problem I has was a typical one in kerberos setups... DNS and name resolution has to work.
In this case a simple entry in the hosts file with a non-fqdn and there are very few clues.

So maybe you'll google some of that and it'll help... :)