How to Use SSH Multiplexing and Control Commands

Updated: 22 October 2026 · Applies to: OpenSSH client

If you regularly connect to the same server for remote logins, administration or automated tasks, SSH multiplexing reuses one existing connection instead of negotiating a new one every time, which noticeably speeds up repeated connections. Knowing the control commands also helps when a multiplexed session hangs, for example after an IP change, a VPN reconnect, or a firewall interruption.

Set up multiplexing

Create a folder to hold control sockets:

mkdir -p ~/.ssh/controlmasters/

Start a master connection:

ssh -M -S ~/.ssh/controlmasters/server-socket username@hostname

• -M: enables master mode.
• -S: path for the control socket, created automatically.
• username@hostname: your SSH username and the server's address.

If the server uses a non-default SSH port:

ssh -p PORT_NUMBER -M -S ~/.ssh/controlmasters/server-socket username@hostname

After that, connect normally, without -M or -S:

ssh username@hostname

Set it up automatically with SSH config

Instead of typing the socket path every time, add this to ~/.ssh/config:

Host myserver
    HostName SERVER_ADDRESS
    User USERNAME
    Port 22
    ControlPath ~/.ssh/controlmasters/%r@%h:%p
    ControlMaster auto
    ControlPersist yes

Then just connect with:

ssh myserver

Or apply it to every host at once:

Host *
    ControlPath ~/.ssh/controlmasters/%r@%h:%p
    ControlMaster auto
    ControlPersist yes

Manage an existing multiplexed connection

Once a master connection exists, control it with ssh -O:

Check whether the master is running:

ssh -O check username@hostname

Close it safely, letting existing sessions finish:

ssh -O stop username@hostname

Close it immediately, ending every session on it:

ssh -O exit username@hostname

Prefer stop over exit unless you specifically need to end active sessions right away.

Forward a port over the multiplexed connection

ssh -O forward -L LOCAL_PORT:REMOTE_HOST:REMOTE_PORT username@hostname

Cancel it again:

ssh -O cancel username@hostname

For example, to forward a web service on the remote side:

ssh -O forward -L 8443:10.0.0.1:8443 username@hostname

See the speed difference for yourself

With multiplexing (after a master connection is already open):

time ssh username@hostname true

Without it:

time ssh -o 'ControlMaster=no' -o 'ControlPath=no' username@hostname true

Compare the two times; the multiplexed connection should be noticeably faster since it skips the full handshake and authentication.