You are connected to a remote system thru Telnet/SSH. If Telnet/SSH session is suddenly went into a inaccessible mode, due to system failure or link disconnection or application failure, the Escape sequences will help us to quit from session immediately. Here I listed some of the Escape sequence supported by Telnet and SSH.Telnet:
Pressing CTRL ] or ^], will give you the telnet command prompt (telnet>). In this prompt, you can try the following Escape commands:
- ? — List all commands
- close — Close current connection
- logout — Forcibly logout remote user and close the connection
- display — Display operating parameters
- mode — Try to enter line or character mode (‘mode ?’ for more)
- open — Connect to a site
- quit — Exit telnet
- send — Transmit special characters (‘send ?’ for more)
- set — Set operating parameters (‘set ?’ for more)
- unset — Unset operating parameters (‘unset ?’ for more)
- status — Print status information
- toggle — Toggle operating parameters (‘toggle ?’ for more)
- slc — Set treatment of special characters
- z — Suspend telnet
- environ — Change environment variables (‘environ ?’ for more).
Pressing ~ and a Character combination will execute a particular escape sequence listed below:
- ~. — Terminate connection (and any multiplexed sessions)
- ~B — Send a BREAK to the remote system
- ~C — Open a command line
- ~R — Request rekey (SSH protocol 2 only)
- ~^Z — Suspend SSH
- ~# — List forwarded connections
- ~& — Background SSH (when waiting for connections to terminate)
- ~? — Show this list.
- ~~ — Send the escape character by typing it twice.
Just assume, you are in System A and connected System C through System B like this A–> B–> C. Now the session B–> C is hanged. In this case, if you use the Escape sequence to disconnect the B–> C connection, then normally the session A–> B will be disconnected. Because, the Escape sequnce will processed by the 1st or outer session A–> B. So to pass the Escape sequence to 2nd or inner session B–> C, you have to use the ‘send’ command in Telnet and ‘~~’ sequence in SSH.