How to prevent dropped ssh connections

In honor of Ken Snider (sysadmin at FM, though more famously the much lauded sysadmin for Boing Boing), who told me how to do this.

One of the biggest annoyances I experienced after moving over to Ubuntu was having my SSH sessions time out behind my home wireless router (aka NAT). Though at the time I didn’t realize that was the problem. I thought the server at the other end was “logging me out.”

What made things worse is that when the connection got dropped, GNOME Terminal would completely freeze, no Ctrl-C, no nothing. All I could do was open a new terminal tab and close that one. Mondo-annoying. Occasionally I’d return to a terminal that had been connected to another server via ssh only to find I’d been logged out with the cryptic message:

Write failed: Broken pipe

The same thing with Gnome’s network folders. If I left one open for too long and then tried to copy a file, it’d spin for a few minutes before reporting that it couldn’t connect—and only then would it allow me to abort. Hitting the cancel button in process did nothing. I could either wait and do other things, or force-quit.

What made this irritating coming from Windows, where I’d previously relied upon WinSCP and SecureCRT for my file-transfer and remote connection needs, was that I’d already figured out how to configure both those applications to periodically send what they called NO-OPs or null packets to trick the server (actually the NAT) into keeping the connection alive for as long as I had the application open.

But with a little command line utility like ssh (from OpenSSH), there’s no Edit > Preferences menu, so I figured I was stuck. This is of course where my GUI background shows. Of course ssh has a preferences menu! It’s called ssh_config, and it’s stored as a textfile under /etc/ssh. Doh! Update: as HD mentions in the comments, it’s better to add this to your own local ssh config file here: ~/.ssh/config.

And thanks to Ken I learned that by adding the following line to ssh_config, (not sshd_config, he warned), “ssh will send a message through the encrypted channel [every 120 seconds] to request a response from the server.”

ServerAliveInterval 120

In other words, no more prematurely dropped ssh connections!

Feel free to if you found this useful.

4 Comments

Oh man! This is going to save my life. Ubuntu, OpenSSH, etc, why isn’t this option enabled by default?

very nice tip, this is very helpful when managing remote linux boxes.

originalgeek

Thanks. Big help.

HD

Okay old post I know – you should set these things in your own ssh config file – it resides in ~/.ssh/config

Better to keep things in your home dir, then you can back it up easily and you don’t change possible other users settings.

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