tmux/Q/What do I need to know if I'm in tmux when I ssh into a server and use tmux?

• What do I need to know if I'm in tmux when I SSH into a server and use tmux?

  • AI Answer

    • Short answer: The outer tmux intercepts your prefix key before it reaches the inner tmux. Press the prefix twice to send it to the inner session. Also watch for TERM terminfo mismatches on the remote.

    • Prefix key collision

      • Both outer (local) and inner (remote) tmux listen on the same prefix (Ctrl+b by default).
      • Pressing Ctrl+b <key> acts on the outer session.
      • To send a command to the inner session, press the prefix twice: Ctrl+b Ctrl+b <key>.
        • Examples:
          • Ctrl+b Ctrl+b c — new window in the inner session
          • Ctrl+b Ctrl+b d — detach from the inner session (leaves SSH open)
          • Ctrl+b Ctrl+b [ — enter copy mode in the inner session

    • TERM terminfo mismatch

      • Inside tmux, TERM is set to tmux-256color (or screen-256color). Remote servers often lack that terminfo entry, causing display artifacts or errors.
      • Quick fix — set TERM to a widely available value before SSHing:

        • TERM=xterm-256color ssh user@host

      • Or in ~/.ssh/config:

        • Host myserver
              SendEnv TERM

        • (requires AcceptEnv TERM on the server's sshd_config)
      • Permanent fix — install the tmux terminfo on the remote once:

        • infocmp tmux-256color | ssh user@host -- tic -x -

    • Double status bar

      • Both sessions show their own status bar. You get two stacked bars at the bottom while nested. This is normal and harmless; just visually noisy.

    • Using a different prefix for the inner session

      • A common convention: configure the remote ~/.tmux.conf to use a different prefix (e.g. Ctrl+a) so the two sessions are unambiguous.

        • # on the remote server's ~/.tmux.conf
          set-option -g prefix C-a
          bind-key C-a send-prefix

    • The $TMUX environment variable

      • Inside any tmux session, $TMUX is set. The SSH connection starts a fresh environment on the remote, so $TMUX does not propagate to the remote server's shell. Remote tmux starts cleanly regardless.

    • Sources

      • tmux FAQ — Nesting
      • Super User — How to use tmux when logged into a remote server that also uses tmux