SSH provides special escape sequences that allow you to control or terminate sessions when keyboard input is otherwise being sent to the remote server. This guide explains how to use these powerful shortcuts.

Understanding SSH Escape Sequences

When connected to a remote server via SSH, normal keyboard input is forwarded directly to the remote system. This creates a challenge if you need to control the SSH connection itself rather than sending commands to the remote server.

SSH solves this problem with escape sequences - special key combinations that are intercepted by the SSH client rather than being sent to the remote server.

Terminating a Stuck SSH Session

To immediately terminate the current SSH session (especially useful when a session is frozen):

1. Press Enter (to ensure you’re at the beginning of a line)
2. Press ~ (tilde)
3. Press . (period)

This key sequence (Enter → ~ → .) will immediately close the connection.

Available Escape Sequences

To view all available escape sequences during an active SSH session:

1. Press Enter
2. Press ~
3. Press ?

~.  - terminate session
~B  - send a BREAK to the remote system
~R  - Request rekey (SSH protocol 2 only)
~#  - list forwarded connections
~?  - this message
~~  - send the escape character by typing it twice

Important Notes About Escape Sequences

• Timing matters: Escape sequences are only recognized immediately after pressing Enter (at the beginning of a new line)
• After viewing the list of escape sequences, press Enter to return to your session

Working with Nested SSH Sessions

When you have multiple SSH sessions nested inside each other (connecting from one server to another), you can target specific connection levels:

• Because typing ~~ sends a literal ~ to the remote system, you can use multiple tildes to target nested connections
• The number of tildes corresponds to the depth of the connection you want to target
• For example, to terminate the fifth-level SSH connection while keeping the other four intact, type: Enter → ~~~~.

Reference

This information is adapted from this AskUbuntu answer.