pix-proc

Pi tool to run and manage long-lived processes that must outlive a single agent turn — npm run dev, vite, python main.py, or a test watcher. The proc tool starts a detached process, the child writes its own output to a log file, and the agent manages it by a short proc-* handle.

Why not bash

bash is synchronous: it blocks until the command exits, then returns. It cannot supervise a process that keeps running. proc starts a process, returns a handle, and lets the agent keep working, then read output, or stop it later. For one-shot commands use bash — proc start reports and steers you back when a command exits fast.

Tool

The proc tool supports five actions:

Action	Required input	Result
start	command	Spawns a detached process, returns a proc-* handle plus its first output (short wait window)
list	None	Lists processes with handle, command, uptime, status, and last output line
logs	handle	Returns new output since your last read; pass tail for the last n lines
stop	handle	Sends SIGTERM to the whole process group, then SIGKILL after a 2s grace
rm	handle	Removes a stopped process and its log file (refuses while running)

start also accepts cwd (working directory, default the session cwd) and name (a friendly label). logs accepts tail (integer, max 1000).

Example calls:

proc({ action: "start", command: "npm run dev" });
proc({ action: "list" });
proc({ action: "logs", handle: "proc-swift-otter-42" });      // new lines since last read
proc({ action: "logs", handle: "proc-swift-otter-42", tail: 50 }); // last 50 lines
proc({ action: "stop", handle: "proc-swift-otter-42" });
proc({ action: "rm", handle: "proc-swift-otter-42" });

Log model

• The whole stdout+stderr is kept on disk at ~/.cache/pi/proc/<handle>.log. The complete output stays available for a human to read directly.
• logs never dumps the whole file. By default it returns only the lines added since your last logs call for that handle (a per-handle cursor), capped at
  1000. tail n forces the last n lines and does not move the cursor.
• The cursor holds at the last newline, so a half-written line is never returned.

Cap

Each log is capped at 50 MB. At the cap the tool stops recording — it does not rewrite or drop older lines, so the file stays intact and complete up to the cap. The process keeps running. logs, list, and the widget report capped.

Process lifecycle

• Processes are spawned detached, each leading its own process group. stop kills the whole group (kill -pgid), so vite/esbuild children do not survive as orphans holding a port.
• Every running process writes a pidfile with its process-group id and start time. On the next session start, pix-proc finds orphaned groups left by a crashed session, lists them, and asks before killing — never silently.
• On a clean session shutdown, pix-proc stops every process it owns.

User command

/proc lets you inspect and control processes without the model:

• /proc — open the process modal. The list shows each handle, command, uptime, and status.
  • enter opens a process: its details, the last 200 log lines (PgUp/PgDn to scroll), and a Stop or Remove action.
  • s stops the selected running process. r removes the selected finished process and its log.
  • esc goes back, then closes. Each stop or remove shows a notification with the result.
  • The modal refreshes every second: status, uptime, and the open log tail stay current.

Without a TUI (headless or RPC), /proc prints the process list as a notification.

Limits

Processes are attached to the Pi session and stop when the session ends. A survive-restart daemon, a restart action, a pix.json config section, and stdin/TTY passthrough for watchers that need a PTY are outside current scope.

Development

bun test packages/pix-proc
bun run check
bun run typecheck

bun run typecheck checks the full monorepo, not only this package.

Install

pi install npm:@xynogen/pix-proc

Standalone and opt-in. @xynogen/pix-core does not bundle it. It starts background processes.

Install @xynogen/pix-gate for command gating on proc, the same gate that guards bash. Without pix-gate, proc start is exactly as ungated as bash is without pix-gate — the same trust surface.

Full distro

This package is part of Pix. The installer sets up Pi and the full distro. See Install for the notes for each OS.

# Linux / macOS
curl -fsSL https://raw.githubusercontent.com/xynogen/pix-mono/main/scripts/install.sh | sh

# Windows
irm https://raw.githubusercontent.com/xynogen/pix-mono/main/scripts/install.ps1 | iex

License

MIT. See LICENSE.