How to Keep SSH Sessions Alive: Prevent Timeout on Client and Server

1. Overview

Many times we want to keep an SSH session connected to keep applications running or avoid frustration when returning to the terminal. This tutorial shows how to prevent SSH session timeout until you close the terminal window.

2. Why does SSH close the connection?

The SSH daemon (sshd) on the server must stay running. If the SSH client does not send data for a period, the server will close the connection. To prevent this, you can configure either the client or the server.

3. Configuration files

Several configuration files can be modified to keep SSH sessions alive. The steps differ for client and server configurations.

3.1 Client configuration

Client configuration file location: $HOME/.ssh/config If the file does not exist, create the .ssh directory and the file:

mkdir $HOME/.ssh

touch $HOME/.ssh/config

Set the file permissions so only the owner can read/write: chmod 600 $HOME/.ssh/config Edit the file with your preferred editor (e.g., nano or vim) and add the desired settings. For a specific host:

Host example</code>
<code>    Hostname example.com</code>
<code>    ServerAliveInterval 240

The ServerAliveInterval option defines how many seconds the client waits before sending a keep‑alive signal.

To apply the setting to all hosts, use a wildcard:

Host *</code>
<code>    ServerAliveInterval 240

You can also limit the number of unanswered keep‑alive messages with ServerAliveCountMax:

Host *</code>
<code>    ServerAliveInterval 240</code>
<code>    ServerAliveCountMax 2

If the client does not receive a response twice, it will close the SSH session.

3.2 Server configuration

Server‑side configuration file location: /etc/ssh/sshd_config.

Add the following lines (note the use of ClientAliveInterval instead of ServerAliveInterval):

ClientAliveInterval 60</code>
<code>ClientAliveCountMax 2

ClientAliveInterval

is specified in seconds; if the server does not receive data from the client within this interval, it sends a request for a response.

3.3 Why not set the connection to never disconnect?

Keeping an SSH session permanently open can be costly on cloud platforms that charge per minute of server usage, even when the session is idle. Setting reasonable timeouts helps avoid unnecessary charges.

4. Conclusion

We have learned how to create SSH configuration files on both client and server, which settings prevent SSH session timeout, and why it is generally better not to disable timeouts entirely.