User guide Telnet and Mosh

Telnet and Mosh

The toolbar More menu opens Telnet… and Mosh… quick-connect dialogs; both can also be saved as sessions (see Saved sessions).

Telnet uses a built-in client (host, port 23 by default, 15 s connect timeout).

  • Telnet is not encrypted: everything typed, passwords included, crosses the network in clear text. The tab starts with a yellow "Telnet is not encrypted." line.
  • Option negotiation: the server may enable ECHO and SUPPRESS-GO-AHEAD; PlexusTerm offers TERMINAL-TYPE (xterm-256color) and the window size (NAWS, sent again on every resize) and refuses every other option.
  • Enter is sent as CR NUL (a bare carriage return as RFC 854 requires); byte 255 is escaped in what you type and Telnet commands never reach the terminal.

Mosh keeps a session alive across roaming, sleep and flaky links. It logs in with a saved SSH session (its key, agent or password, saved keyring password and jump hosts all apply), runs mosh-server new -s -c 256 -l LANG=en_US.UTF-8 there (override it per session with Server command), closes the SSH connection and starts the local mosh-client in the tab.

  • Requirements: mosh installed on both machines (sudo apt install mosh), and UDP ports 60000-61000 on the server reachable from this machine (open them in the server's firewall). Jump hosts are only used for the SSH login: the UDP traffic goes straight to the server's address.
  • The Mosh session key reaches mosh-client only through its environment (MOSH_KEY): never on its command line, in a log or in the user interface.
  • mosh-client not found — install mosh means mosh is missing on this machine; mosh-server not found on the server — install mosh there means it is missing on the server. If mosh-client fails, the tab stays open with its message and exit code.