On most of my Ubuntu servers, I found that logging in took 15-30 seconds when using SSH. Eventually I narrowed down the problem to three different causes.
The hostname took a while to lookup
My server hostnames look like this: someserver.sparkcreek.ca. Apparently the DNS lookup for this was taking a while, when it didn’t need to. I just added two aliases to my /etc/hosts file, for someserver and someserver.sparkcreek.ca. My /etc/hosts file now looks like this:
127.0.0.1 localhost someserver.sparkcreek.ca someserverSSH reverse DNS lookups took a while
SSHd will attempt to do a reverse DNS lookup on any IP connecting to it, but most client machines out there won’t have reverse DNS configured (even if they do, it’s not something you need). You can disable this by adding UseDNS No to your /etc/ssh/sshd_config file.
Disable GSSAPIAuthentication
See https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/84899
Just add GSSAPIAuthentication no to your /etc/ssh/sshd_config file.
Aftermath
SSH logins now take ~2 seconds instead of 15-30 seconds.
Thanks, i’ve changed my hosts too, my old hosts pointing my hostname into real public IP instead 127.0.0.1 🙂