How to check SSH multiplexing session status

Monitoring the status of multiplexing sessions in SSH is crucial for effective connection management. SSH multiplexing allows multiple sessions to use a single network connection, which reduces resource consumption. Knowing how to check these sessions ensures they are working as intended.

In SSH multiplexing, a master connection is established, which other sessions can reuse. This setup saves time and reduces network load. However, regular checks are necessary to confirm that these sessions are operating correctly.

To check the status of multiplexing sessions, specific commands can be used. This helps in managing active connections and resolving potential issues. Consistent monitoring is key to maintaining a secure and efficient SSH environment.

1. Open the terminal on your local machine.

   $ ssh user@remotehost

2. Identify the location of the control master socket used for multiplexing, typically stored in /tmp or as specified in your SSH configuration.

   $ ls /tmp/ssh-*

3. Check if the control master process is running.

   $ ps aux | grep ssh | grep -E 'master|mux'
   username           35857   0.0  0.0 410883376   1920   ??  Ss    8:15PM   0:00.00 ssh: /tmp/62edf122603cf5b7a9c9fd3244cbcf83da747026 [mux]
   username           35854   0.0  0.0 411015568   2528   ??  Ss    8:15PM   0:00.01 ssh: /tmp/aaa521a6f23ded0a5d140da32386a0f9ffaec157 [mux]

   The control master process manages all multiplexed sessions.

4. Verify active multiplexed connections by inspecting the control master socket.

   $ lsof -U | grep /tmp/62ed*
   ssh       35857 username    3u  unix 0x64513004a8a01fe6      0t0      /tmp/62edf122603cf5b7a9c9fd3244cbcf83da747026.Io3LXrQdDcdwRcJk
   ssh       35857 username    6u  unix 0xaf4cb928ce99e1c9      0t0      /tmp/62edf122603cf5b7a9c9fd3244cbcf83da747026.Io3LXrQdDcdwRcJk

5. Optionally, display detailed status information for each multiplexed session using the SSH verbose mode if needed.

   $ ssh -vvv -O check user@remotehost

   Increase verbosity to debug and view detailed session status.

6. Terminate any unnecessary multiplexed sessions by stopping the control master process if no longer required.

   Related: How to stop multiplexing sessions in SSH