How to keep SSH sessions alive

This article describes how to change the amount of time SSH sessions are alive.

Note: You need ‘root` access to complete the following steps.

For system-wide

The Host value, which you can name anything you want, is simply a label for the other settings. To enable the keep-alive system-wide, edit the file /etc/ssh/ssh_config:

Host examplehost Hostname examplehost.com ServerAliveInterval 180 ServerAliveCountMax 2

For client-side

To make your OpenSSH server keep all connections alive with clients, add the following to /etc/ssh/sshd_config:

ClientAliveInterval 300 ClientAliveCountMax 2

Important: These settings make the SSH client or server send a null packet to the other side every 300 seconds (five minutes) and give up if it doesn’t receive any response after two tries. At that point, the system likely discarded the connection anyway.

ServerAliveCountMax parameter

This parameter sets the number of server alive messages, which the system might send even if SSH1 receives no messages from the server. If the number of server alive messages exceeds the threshold value, SSH disconnects from the server, terminating the session.

ServerAliveInterval parameter

This parameter sets a timeout interval in seconds. If the process receives no data from the server after this limit, SSH1 sends a message through the encrypted channel to request a response from the server. The default, 0, indicates that the system doesn’t send these messages to the server, and 300 shows that you set the BatchMode option. This option applies to protocol version 2 only. ProtocolKeepAlives and SetupTimeOut are Debian-specific compatibility aliases for this option.

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