I am trying to SSH into a server and it hangs at login

I am trying to SSH into a server and it hangs at login. This is the output of ssh -v:

OpenSSH_5.8p1 Debian-1ubuntu3, OpenSSL 0.9.8o 01 Jun 2010 debug1: Reading configuration data /etc/ssh/ssh_config debug1: Applying options for * debug1: Connecting to $$$$$$ [888.888.888.888] port 22. 

I have generated ssh-keys on the client and placed its public key (id_rsa.pub) in the host's authorized_keys.

All machines are connected with a physical cable, not wireless. I can successfully ssh from the client to another separate machine on the same network, and I can also ssh from that separate machine to the host successfully. Finally I am able to SSH from host to client. But when I try to SSH from client to host it hangs.

What could be the issue?

2 Answers

Take a look at this blog post: “Troubleshooting sshd server configuration.”

Especially the part,

1. run /usr/sbin/sshd -d -D -p 222 on the server.
2. run ssh -v -C -A -X -p 222 on the client.

Normally the log on the server side will reveal what went wrong.

I had the same issue (on MacOS), but did not have the option to run anything on the server side as the accepted answer suggests. I went through many troubleshooting steps (see below), and in the end it seems like I have some DNS issue which is blocking the connection to the port, and for some reason I am not getting a Could not resolve hostname error. IT support confirmed that none of my login requests were coming through to the host.

Eventually what worked was to run nslookup server.domain-name.de to find the IP address. It returns:

Server: XXX.XXX.XXX.XXX Address: XXX.XXX.XXX.XXX#XX Name: server.domain-name.de Address: XXX.XXX.XX.XXX 

Using the second Address, I tried logging in again as follows: ssh which worked fine!

Other troubleshooting steps which did not work for me but might work for others:

• In System Preferences > Sharing, check that Remote Login is enabled for all users
• Use the Network Utility app (easily found through Spotlight with CMD + Space, Network Utility) enter the server domain name and scan for open ports. This told me that port 22 was indeed open.
• I went to ~/ssh/ssh_config and added GSSAPIAuthentication no to the uncommented options in the lines below Host *.
• I restarted my MacBook, checked my firewall was off, and tried on a VPN.
• I tried ssh localhost, which worked. I tried to connect to a different server, but had the same problem of being stuck on connecting to port 22.
• And of course I checked that my username was spelled correctly.
• Once we figured out it was likely a DNS issue, we tried flushing the DNS cache:

  sudo killall -HUP mDNSResponder sudo killall mDNSResponderHelper sudo dscacheutil -flushcache 

  but this didn't fix the issue for me.