SSH connection freezes after bigger output when inactive for a while

Question

I have a problem with an SSH session freezing after using it again when it was idle for a while.

The problem is that the session doesn't freeze immediately, I can still use it. But as soon as a command sends more data, it freezes before any output arrives, and I have to restart the terminal.

If have read earlier solutions about MTU, but there, the session freezes everytime. Here it only happens after a period of inactivity.

Note that I have set ServerAliveInterval 120 in .ssh/ssh_config

Any clues about how I can solve this?

• MattBianco: Is there a firewall between the client and server?
• Ikke: There probably is, though I have no control over it (corporate firewall).
• MattBianco: I think the first bullet in my answer will be helpful. Especially in conjunction with the first few lines of man ssh_config.
• George M: Change ~/.ssh/ssh_config to ~/.ssh/config. Make sure the permissions on it are 600.
• MattBianco: Note that my answer (the first) contains the solution as well as some other hints towards troubleshooting ssh :-)

Answer 1

Change ~/.ssh/ssh_config to ~/.ssh/config. Make sure the permissions on it are 700.

This discussion has a lot of good information. You can also follow the tag for ssh (just click on /ssh under your question) to go to a tag wiki for more information and trouble shooting guidance.

• Ikke: I had named it wrong. After renaming it, I (so far) didn't have any freezes anymore.

Answer 2

Suggestions:

• Try setting the ServerAliveInterval, ServerAliveCountMax, and TCPKeepAlive options on the command line instead of through ssh_config, to rule out that there is a problem reading your settings. Perhaps the ssh_config should be called just config instead?
• Use the verbose flag (more than once) to increase chances of an explanatory error message
• Make sure the ServerAliveInterval * ServerAliveCountMax is less than the firewall's idle time threshold before tearing down your ssh session (ask your network admin).
• If the server is yours, you could try the ClientAlive*-options there.
• Check for version incompatibilities if not OpenSSH on both client+server.

Answer 3

you can set up your client to send the tcp keep alive messages. I know it is under the connection options in putty. Not sure on the command line options but this solved it for me when I was having problems. Though it only did it to me on the win7 machines at school.