Prevent your SSH connection from freezing

Recently I was finding that my SSH connection to a Media Temple (dv) Centos 5 server was freezing. Creating a local config file fixed it. For anyone else suffering the same problem here's how to do it.

The Issue

I'm on Mac OSX 10.5 connecting to a Centos 5 box using Terminal. I'm using shared keys and the connection was fine and working well until I left the Terminal window idle for over 15 seconds. I was also finding that SFTP sessions via Transmit would regularly freeze. All of this was very annoying and frustrating.

The solution

I discovered that through creating a local config file for ssh you can declare settings that fix this and many other issues. Remember I'm on a Mac OSX 10.5 here. The usual disclaimer applies - this article is unsupported and you make changes at your own risk.

Open terminal and get going:

cd /Users/yourname/.ssh

# If you get ""-bash: cd: .ssh: No such file or directory"
# You need to create it
mkdir /Users/yourname/.ssh

# Set security on the folder so only you can read, write and execute
chmod 700 /Users/yourname/.ssh

# Change directory
cd .ssh

# Create the config file
touch config

# Edit the config file
vi config

# When in vi hit i to enter insert mode and add the following lines to the config file
ServerAliveCountMax 3
ServerAliveInterval 10

# Save and quit by hitting :wq

# Set correct permissions on the config file
chmod 644 /Users/yourname/.ssh/config 

Now try connecting via SSH and this should stop your SSH sessions freezing. This instantly fixed the issue for me anyway. Hopefully it might help a few other people.

Other uses

Through reading the documentation I discovered it is also possible to set configuration on a per user basis for SSH. You can set compression, the port number you are connecting to, specific settings for hostnames and much more.

If you are using SSH on a daily basis having a quick read of the documentation - is likely to throw up a few useful things you can put into a config file.