tmux/Option/status-left-length

• status-left-length

  • A tmux session option setting the maximum width, in columns, of the left component of the tmux/Status Line. The default is 10.
  • It caps rather than reserves. A left component narrower than the cap draws at its own width and the window list begins immediately after it, so raising the cap spends columns only on the sessions whose names need them.
  • Under the default tmux/Option/status-left of [#{session_name}] , the opening bracket takes the first column, so the cap admits status-left-length - 1 characters of the tmux/session/Name — nine at the default 10.

  • Usage

    • Raise it in tmux/Config:
      • sh

        set -g status-left-length 40

    • Or at runtime with tmux/Command/set-option/g:
      • sh

        tmux set-option -g status-left-length 40

    • Read the current value with tmux/Command/show-options/gv:
      • sh

        tmux show-options -gv status-left-length

    • Render the left component exactly as the status line draws it, cap and all:
      • sh

        tmux display-message -p '#{T;=/#{status-left-length}:status-left}'

  • How the cut is made

    • status-format[0] applies the cap as #{T;=/#{status-left-length}:status-left}. The =N format modifier keeps the first N characters and discards the rest.
    • =N takes an optional marker as a second argument — #{=/9/…:session_name} appends … when it trims. The stock status-format supplies none, so a truncated left component stops mid-word with nothing to mark the cut: at the default cap, the session name encode-2026-08-17 draws as [encode-20, and the closing ] is never reached.

  • Set to 40 here, in the config

    • 40 is what lets a full My/AI/Agent/Fleet session name like hayward-2026-08-24 render instead of stopping at [hayward-2.
      • sh

        tmux show-options -gv status-left-length
        # 40

    • It began as a runtime set -g, the same way tmux/Option/status-left and tmux/Option/status-right were on this server — see tmux/Status Line/Q/Why does my status-right repeat the same session name instead of listing every session?. A runtime set -g is server-global and outlives every session on that server, but not the server: on the next tmux kill-server, or the first session after a reboot, the cap would have returned to 10 and long session names would have started being cut again, with nothing to announce it.
    • It is now in the config file. 2026/08/24, set -g status-left-length 40 was added to the chezmoi source for ~/.config/tmux/tmux.conf with a comment giving the reason — My/Dotfiles change track-tmux-status-left-length. A server started from that file reports 40 with no runtime set -g issued to it; the same probe against -f /dev/null reports 10 and renders [hayward-2.
      • sh

        tmux -L slltest -f ~/.config/tmux/tmux.conf new-session -d -s hayward-2026-08-24
        tmux -L slltest show-options -gv status-left-length            # 40
        tmux -L slltest display-message -p '#{T;=/#{status-left-length}:status-left}'
        # [hayward-2026-08-24]
        tmux -L slltest kill-server

      • An isolated socket is the way to check this while a fleet is attached — kill-server on the default socket would take every seat's session down with it.
    • The neighbouring status options are not in the config, and do not need to be. Measured 2026/08/24 on tmux/v/3.7b against a -f /dev/null server, tmux/Option/status-left, tmux/Option/status-right, tmux/Option/status-right-length, status-style and status-interval on the running server are identical to stock — the set -gu restore proposed on the status-right question page has been applied. status-left-length was the only status option left departing from stock.