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Delayed SSH login on CentOS 6

Nathan — Thu, 01 Sep 2011 15:01:59 +0000

I’ve setup several CentOS 6 virtual machines recently and they all have the same delayed SSH login problem. I’ve found a solution to this problem and I’m documenting it here so I can find it next time!

I originally found this fix at http://www.walkernews.net/2009/04/06/how-to-fix-scp-and-ssh-login-prompt-is-very-slow-in-linux/ and it’s not specific to CentOS 6, but I’ve only observed this delay problem on CentOS 6.

Now, on to the problem. SSH logins to these CentOS 6 servers were delayed by about 30 seconds. (I never timed it exactly, but it was long enough to be very frustrating when you’re trying to get work done) When logging in using ssh -vvv user@hostname the debug output shows the delay happens at these lines:
debug3: authmethod_is_enabled gssapi-with-mic debug1: Next authentication method: gssapi-with-mic debug1: An invalid name was supplied Cannot determine realm for numeric host address
debug1: An invalid name was supplied Cannot determine realm for numeric host address
debug1: An invalid name was supplied

The solution appears to be disabling the GSS API authentication method on the SSH server.

To disable GSS API, first open/etc/ssh/sshd_config in your favorite editor
vim /etc/ssh/sshd_config
Then find the line that says
GSSAPIAuthentication yes
Change it to
GSSAPIAuthentication no
and save the file. Finally, restart the sshd service.
service sshd restart

SSH logins should now be quick as usual!

Back on my normal server

Nathan — Sat, 20 Jun 2009 00:58:23 +0000

I’m back on my normal server again. I had complete data loss and my backups weren’t as thorough as they should have been so I had to rebuild my configuration.

Moral of this story: if in doubt, back it up.

Recovering from scratch

Nathan — Wed, 10 Jun 2009 02:50:28 +0000

My web server was one of the 4,000 or so servers affected by the Vaserv HyperVM hack that started Sunday (June 7th), and my site has been down since then. I had a complete backup of all my web content that was made a couple hours before the outage started, so I’ve been able to restore pretty much everything. Many others were not so lucky… just another reason to make sure you have a backup system in place.

My site may be slow until my regular server comes back online, because the backup host I’m using isn’t very fast.

A new look for njcrawford.com

Nathan — Thu, 21 May 2009 02:59:49 +0000

Now sporting WordPress for the home page. Woohoo!

Next step: make the rest of the site look nice too.