Why is my SSH login slow?

Solution 1:

Try setting UseDNS to no in /etc/sshd_config or /etc/ssh/sshd_config.

Solution 2:

When I ran ssh -vvv on a server with a similar slow performance I saw a hang here:

debug1: Next authentication method: gssapi-with-mic

By editing /etc/ssh/ssh_config and commenting out that authentication method I got the login performance back to normal. Here's what I have in my /etc/ssh/ssh_config on the server:

GSSAPIAuthentication no

You can set this globally on the server, so it doesn't accept GSSAPI to authenticate. Just add GSSAPIAuthentication no to /etc/ssh/sshd_config on the server and restart the service.

Solution 3:

For me, the culprit was IPv6 resolution, it was timing out. (Bad DNS setting at my host provider, I guess.) I discovered this by doing ssh -v, which showed which step was hanging.

The solution is to ssh with the -4 option:

ssh -4 [email protected]