What tmux actually is

Most tutorials start with keybindings. That's backwards — tmux has maybe eight ideas, and once you have the model, the keys become obvious. Here's the model.

The one-sentence version

tmux keeps your terminal work running in a background process (the server), and lets any terminal connect to it, disconnect from it, and split it into as many screens as you want. Terminal crashes, laptop closes, SSH drops — your work doesn't notice.

The hierarchy

One server runs per user, silently, started on demand. It holds sessions (workspaces — one per project is the classic setup). A session holds windows (like browser tabs, listed in the status bar at the bottom). A window holds panes (split terminals you see at the same time). Your terminal is just a client — a viewport that attaches to one session.

the whole model
server (one, invisible, holds everything)
└── session "work"          ← you attach to this
    ├── window 0: editor    ← like a tab
    │   ├── pane: nvim
    │   └── pane: tests     ← splits you see together
    └── window 1: server
        └── pane: npm run dev
└── session "ops"
    └── window 0: ssh prod

Why this design matters

Because the server owns everything, "closing your terminal" and "losing your work" become unrelated events. This is what tmux is *for*. The splits and tabs are nice; detach/reattach is the feature.

The prefix key

Your keystrokes go to the program in the pane — so tmux needs a way to know a key is meant for *it*. That's the prefix: press Ctrl-b, release, then press a command key. Ctrl-b c means "tmux: new window". Every tmux keybinding works this way, and when you see prefix + c written anywhere, that's what it means.

Before moving on

  1. Install tmux (brew install tmux / apt install tmux)
  2. Run: tmux new -s hello
  3. You're in — note the status bar at the bottom
  4. Type exit to close it again
[tmuxlab]
^B