The Infraternal Multiplexer

Infraternal keeps every terminal alive on its host, so you rarely need tmux or Zellij on top of it.

What it does for you

Every terminal you open in Infraternal is a session. A session keeps your shell running on the host, whatever happens to the screen you are looking at. That is the job of a multiplexer, so Infraternal has one built in.

Sessions survive disconnects. Close the tab, lose the connection, lock the phone or put the laptop to sleep. The shell and everything in it keep going on the host. Open the app again and the window shows the screen where you left it, then catches up with the live output.
Sessions survive upgrades. Each session has its own small process, separate from the Infraternal agent (the program that runs on each host). The agent can upgrade and restart without ending your shells.
The same session on every device. Start a build on the laptop, look at it from the phone.
Windows, not prefix keys. You arrange sessions as windows on the canvas. There is no prefix key to learn, and no status bar drawn inside the terminal.

Figure pending

Every session is a window on the canvas, so you move between them with the canvas, not with a prefix key.

Why you may want to switch

If your shell starts tmux¹ or Zellij² by itself (a line in ~/.zshrc, ~/.bashrc or your fish config), every Infraternal terminal ends up as a multiplexer inside a session. That means two scrollbacks, two sets of keys and two things that can hold on to a screen.

Why most people do not need the second layer

Sessions already keep your shell alive. What tmux or Zellij add on top is mostly what a session gives you without them: a shell that outlives the screen, and the same shell from another device.

Running both costs you something every day (two scrollbacks, two sets of keys) and buys you little, so Infraternal offers to remove the second layer. It never does so on its own.

The question Infraternal asks

When Infraternal sees tmux or Zellij start automatically in a new terminal, it asks once for that host:

tmux started automatically. Would you like to switch to the Infraternal Multiplexer instead?

Figure pending

Answering the question: the tick shows the exact change first, and Restore puts the original line back.

Button	What it does
✓	Switches. Infraternal shows you the exact change first and edits the file only after you confirm.
✗	Keeps tmux or Zellij as it is, and does not ask again on this host.
?	Opens this page.

Offer To Switch

You find it in Settings under Multiplexer.

How switching works

Every Infraternal session sets the variable INFRATERNAL_SESSION. Switching adds one condition in front of the line that starts the multiplexer, so that line runs only when the variable is empty:

# before
exec tmux new-session -s main
# after
[ -n "$INFRATERNAL_SESSION" ] || exec tmux new-session -s main

Only Infraternal terminals change. An SSH login from another terminal, a console, or any shell without the variable still starts tmux or Zellij as before. You can also start either one by hand in any terminal, whenever you like.

Why a condition and not a rewrite

The line stays where you wrote it, with the same command, so everything else about your startup keeps working. Only the terminals that Infraternal started skip it. If you ever stop using Infraternal, the line still does what it did before.

What stays untouched

Which files it can edit

Infraternal edits these startup files in your home directory, when the multiplexer is started by a line of its own (optionally with exec):

bash and sh: .bashrc, .profile, .bash_profile, .bash_login
zsh: .zshenv, .zprofile, .zshrc, .zlogin
fish: config.fish and conf.d/*.fish

Undoing a switch

After a switch, the notice offers Restore with the file's name. It puts the original line back, and only that line, so other edits you made to the file since are kept.

Sessions from the command line

The app is where you use sessions. The infraternal command is for automation: scripts, and AI agents such as Claude or Codex that need to start a build, watch it and read its output. It never attaches you to a session.

The sessions commands

Command	What it does
`infraternal sessions [<machine>]`	List sessions
`infraternal sessions new <machine> --name <n> [-- cmd]`	Start a session
`infraternal sessions send <machine>:<session> '<text>'`	Type into a session
`infraternal sessions read <machine>:<session> --last N`	Read recent output
`infraternal sessions wait … --until-idle <d>` or `--match <re>`	Wait for a quiet moment or for text
`infraternal sessions watch …`	Follow output, read-only
`infraternal sessions rename …` and `close …`	Rename or end a session
`infraternal sessions mcp`	Offer sessions to AI agents as an MCP server³

Every command takes --json. To put a session on your screen, use infraternal canvas open <machine>:<session>.

The tmux commands it understands

AI agents already know tmux commands, so the same sessions answer to a small subset of them: new-session, send-keys, capture-pane, list-sessions, kill-session and split-window. Anything else fails with a clear "not supported", and attaching is never part of it.

What needs approval

What works today

References

tmux, a terminal multiplexer: the multiplexer many people start from their shell's startup file.
Zellij, a terminal workspace: the other multiplexer the question looks for.
Model Context Protocol: how an AI agent is offered tools and data.