Fixing a slow SSH prompt

For owners of multiple Linux machines, it's happened to all of us -- the machine in the living room responds immediately to SSH; but it takes forever to log in to the one in the closet, although it does succeed eventually.

This happens because of the SSH client attempting various authentication methods. Using ssh -vvv user@host, the output of a slow connection will look something like this:

debug3: check_host_in_hostfile: filename /home/drsavoye/.ssh/known_hosts
debug3: check_host_in_hostfile: match line 11
debug1: Host '192.168.2.107' is known and matches the RSA host key.
debug1: Found key in /home/drsavoye/.ssh/known_hosts:11
debug2: bits set: 499/1024
debug1: ssh_rsa_verify: signature correct
debug2: kex_derive_keys
debug2: set_newkeys: mode 1
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug2: set_newkeys: mode 0
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug2: key: /home/drsavoye/.ssh/id_rsa (0xb7f541a8)
debug2: key: /home/drsavoye/.ssh/identity ((nil))
debug2: key: /home/drsavoye/.ssh/id_dsa ((nil))
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug3: start over, passed a different list publickey,gssapi-keyex,gssapi-with-mic,password
debug3: preferred gssapi-with-mic,publickey,keyboard-interactive,password
debug3: authmethod_lookup gssapi-with-mic
debug3: remaining preferred: publickey,keyboard-interactive,password
debug3: authmethod_is_enabled gssapi-with-mic
debug1: Next authentication method: gssapi-with-mic
debug3: Trying to reverse map address 192.168.2.107.
debug1: Unspecified GSS failure.  Minor code may provide more information
No credentials cache found

debug1: Unspecified GSS failure.  Minor code may provide more information
No credentials cache found

debug1: Unspecified GSS failure.  Minor code may provide more information


debug2: we did not send a packet, disable method
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering public key: /home/drsavoye/.ssh/id_rsa
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Trying private key: /home/drsavoye/.ssh/identity
debug3: no such identity: /home/drsavoye/.ssh/identity
debug1: Trying private key: /home/drsavoye/.ssh/id_dsa
debug3: no such identity: /home/drsavoye/.ssh/id_dsa
debug2: we did not send a packet, disable method
debug3: authmethod_lookup password
debug3: remaining preferred: ,password
debug3: authmethod_is_enabled password
debug1: Next authentication method: password
root@192.168.2.107's password: 

In this case, GSSAPI is failing alongside publickey-authentication, but unlike publickey, takes much longer to give up. To disable it, edit /etc/ssh/sshd_config and remove or comment out the lines #GSSAPIAuthentication yes and #GSSAPICleanupCredentials yes.