Secure Shell (SSH) is a widely-used protocol for secure remote login from one computer to another. One of the features of SSH is the ability to reuse an existing SSH connection for multiple sessions. This feature, known as “SSH channel reuse”, can save time and resources, especially when establishing multiple SSH connections.
In this article, we’ll explore how to enable and use SSH channel reuse in Linux.
Prerequisites
Before proceeding with this tutorial, you should have:
- Access to a Linux machine with SSH installed
- Basic knowledge of the Linux command line interface (CLI)
Enabling SSH Channel Reuse
To enable SSH channel reuse, you need to edit the SSH configuration file (/etc/ssh/sshd_config) and add the following line:
ControlMaster autoThis line tells SSH to automatically create a connection sharing master socket for each new session, and to reuse existing master connections when possible.
Next, you need to restart the SSH service to apply the changes. On Ubuntu or Debian, you can use the following command:
sudo systemctl restart sshOn other Linux distributions, you may need to use a different command, such as:
sudo service ssh restartUsing SSH Channel Reuse
Once SSH channel reuse is enabled, you can reuse an existing SSH connection by specifying the -o ControlPath option with the path to the master socket file. For example, if you have an existing SSH connection to example.com, you can open a new SSH session over the same connection by running:
ssh -o ControlPath=~/.ssh/example.com.sock example.comThis command tells SSH to use the existing master connection for example.com, which is stored in the file ~/.ssh/example.com.sock. If the master connection does not exist, SSH will create a new one.
You can also specify the -o ControlMaster option to control whether to reuse an existing master connection or create a new one. The possible values are:
auto(default): Create a new master connection if none exists, or reuse an existing one if possible.yes: Create a new master connection even if one exists.no: Do not create a master connection.
For example, to force SSH to create a new master connection, you can run:
ssh -o ControlMaster=yes -o ControlPath=~/.ssh/example.com.sock example.comConclusion
SSH channel reuse is a useful feature that can improve the efficiency of SSH sessions. By enabling SSH channel reuse and specifying the path to the master socket file, you can reuse existing SSH connections and avoid the overhead of establishing new ones. Remember to restart the SSH service after editing the configuration file, and use the -o ControlMaster and -o ControlPath options to control SSH channel reuse in your SSH commands.
