Terminal multiplexer
A terminal multiplexer runs multiple shell sessions inside one terminal window, with splits, tabs, and detachable sessions. tmux and Zellij are the popular ones.
A terminal multiplexer is a program that runs multiple shell sessions inside a single terminal, usually with splits, tabs, and the ability to detach and reattach. The canonical examples are tmux, Zellij, and the older GNU screen. They solve two problems: fitting many CLIs into one window and keeping sessions alive across disconnects.
Why it matters
If you SSH into a server, start a long build, and the connection drops, your build dies with the shell. A multiplexer fixes this — you attach, run the build inside a multiplexer session, and even if the SSH tunnel collapses the session keeps running. When you reconnect, tmux attach or zellij attach drops you back in.
For agentic coding, multiplexers are also the default way to run several Claude Code or Codex CLI instances at once on a single machine. SpaceSpider addresses the same need with a native GUI grid layout, which is easier for local work but not a replacement for tmux on a remote box.
How it works
The multiplexer runs a server process that owns a set of PTYs. Each pane in the UI is a PTY hosting a shell. Client processes (your terminal tab) connect to the server to render panes and forward keystrokes. Because the server persists when the client disconnects, sessions survive.
Layouts are described via keybindings and (in Zellij) layout files. Most multiplexers have a prefix key (tmux's default C-b, Zellij's Ctrl+g) that gates their command vocabulary so key presses don't collide with the shells inside.
How it's used
Common multiplexer patterns:
- Remote development over SSH with session persistence
- Running dev server + test runner + shell in one layout
- Parallel agentic coding panes
- Automated dev environments launched via script
See /compare/spacespider-vs-tmux and /compare/spacespider-vs-zellij.
Related terms
- tmux — the most popular multiplexer
- Zellij — modern Rust alternative
- PTY — the kernel abstraction each pane uses
- Grid layout — SpaceSpider's GUI analog
- Space — SpaceSpider's persistent workspace concept
FAQ
Can SpaceSpider replace tmux?
For local GUI use, yes — a SpaceSpider space with a grid layout is a nicer experience than tmux. For remote servers, no — tmux or Zellij still win because they're a single binary over SSH.
Do I need a multiplexer if my terminal has tabs?
Tabs give you multiple shells but don't persist across disconnects and don't offer splits in the same pane group. A multiplexer adds both.
Related terms
- Agentic codingAgentic coding is software development where an LLM-powered agent plans, edits, runs, and verifies code on its own using tools, not just autocomplete.
- AI pair programmingAI pair programming is a collaboration style where an LLM assistant sits alongside you, suggesting code and reviewing changes in real time as you work.
- ANSI escape codesANSI escape codes are control sequences that terminals interpret for colors, cursor movement, and screen clearing — the language of every modern CLI UI.
- Autonomous agentAn autonomous agent is an AI program that perceives, decides, and acts on its own toward a goal — the architecture behind modern coding CLIs.
- CheckpointA checkpoint is a saved snapshot of file state that lets you roll back an AI coding agent's changes to a known-good point.
- Claude CodeClaude Code is Anthropic's official command-line agent that plans, edits, runs, and verifies code across your repo using Claude models and tool use.