dmn

A lightweight PTY daemon. Spawns a shell in a pseudo-terminal and exposes it over a Unix socket, allowing multiple clients to send commands, attach interactively, or watch the output read-only.

You can read more about how I built this and watch a demo video showcasing dmn in my blog.

Quick start

Install via pip/uv:

Important

The package name is dmn-pty not dmn. I do not maintain that project!

pip install dmn-pty
# or uv
uv tool install dmn-pty

# Start the daemon (default session)
dmn

# attach to it
dmn-attach

# Or with a named session and custom shell
dmn --session work --shell /bin/bash

Or from the repo's root:

# Start the daemon (default session)
uv run -m dmn

# attach to it
uv run -m dmn.attach

# Or with a named session and custom shell
uv run -m dmn --session work --shell /bin/bash

Clients

scripts/client.py — command execution

Send one-off commands to the running shell (starts a REPL):

python scripts/client.py -s work
> echo hi # gets sent to the daemonized session

web/bridge.py — web terminal

A WebSocket bridge that serves a browser-based terminal using ghostty-web

cd web && npm install
uv run --script web/bridge.py --session work
# Open http://127.0.0.1:9001 in a browser

The web UI has session switching, connect/disconnect controls, and a read-only mode. The bridge also supports --force-readonly for sharing a terminal view without allowing input.

How it works

dmn uses a hand-rolled event loop built on a selector. A single-threaded loop manages the PTY, stdin/stdout, a Unix server socket, and all connected clients.

Protocol

Clients connect to a Unix socket ($XDG_RUNTIME_DIR/dmn-{session}.sock) and send newline-delimited JSON:

EXEC — send input to the shell:

{"type": "EXEC", "payload": {"command": "ls -la\n"}}

ATTACH — switch to raw bidirectional mode:

{"type": "ATTACH"}

After the {"ok": true}\n response, the connection is raw: bytes from the client go to the PTY, bytes from the PTY go to the client.

WATCH — read-only attach (output only, input discarded):

{"type": "WATCH"}

Resize (in ATTACH mode)

Terminal size changes are sent in-band as a 6-byte escape sequence:

\x00 R cols_hi cols_lo rows_hi rows_lo

Requirements

• Python 3.14+
• Node/npm (for the web client's ghostty-web dependency)