Keeping Your SSH Connections Alive: Configuring ServerAliveInterval and ServerAliveCountMax

Maintaining a stable SSH connection is essential when working on remote servers. Disconnections due to inactivity can interrupt workflows and be quite frustrating. Fortunately, you can configure SSH to send periodic keep-alive messages, preventing your connection from timing out.

Step-by-Step Guide

1. Open the SSH Client Configuration File

Use your preferred text editor to modify the SSH configuration file. For example, with vim:

sudo vim /etc/ssh/ssh_config

If OpenSSH is installed via Homebrew, the configuration file might be located at:

/usr/local/etc/ssh/ssh_config

2. Modify the Configuration

Add the following lines after the Host * directive to apply these settings to all SSH connections:

    ServerAliveInterval 240
    ServerAliveCountMax 10

• ServerAliveInterval: Specifies the interval (in seconds) at which the client sends keep-alive messages to the server. In this case, every 240 seconds.
• ServerAliveCountMax: Limits the number of keep-alive messages sent without response before the connection is terminated. Here, the client will attempt to send 10 keep-alive messages.

3. Save and Exit

If you’re using vim:

• Press ESC to enter command mode.
• Type :wq and press Enter to save and exit.

4. Test the Configuration

To test if the new settings are working:

• Connect to a remote server using SSH:

  ssh user@your-server
  

• Ensure the connection remains active during periods of inactivity.

Conclusion

With this configuration, your SSH client will actively send keep-alive signals, reducing the risk of unexpected disconnections. Adjust the values of ServerAliveInterval and ServerAliveCountMax as needed to suit your environment.