Forked / Detached Process

Spawn a process that is detached from the parent’s controlling terminal via setsid().

Overview

When forked = true is set in ProcessConfig, ProcessManager::start() adds a pre_exec hook that calls setsid(). This detaches the child process from the parent’s controlling terminal, making it suitable for daemons and background services that should survive terminal close.

Unlike a double-fork (which would create a grandchild and lose the Child handle), setsid() keeps the process as a direct child. This means:

• The Child handle is retained in the DashMap
• try_wait() works for reaping and is_running() checks
• stop() / stop_label() can still terminate it
• The reaper thread can detect its exit

graph TD
    classDef default fill: #1e1e1e, stroke: #333333, stroke-width: 1px, color: #ffffff
    classDef parent fill: #00a1e4, stroke: #ffffff, stroke-width: 2px, color: #ffffff
    classDef fork fill: #f5b700, stroke: #333333, stroke-width: 2px, color: #000000
    classDef child fill: #89fc00, stroke: #333333, stroke-width: 2px, color: #000
    classDef detached fill: #dc0073, stroke: #333333, stroke-width: 1px, color: #ffffff

    P["Parent Process<br/><small>ProcessManager</small>"]
    P -->|"fork + exec<br/>+ setsid() in pre_exec"| C["Child Process<br/><small>new session leader</small>"]
    C --> D["Detached from<br/>controlling terminal"]
    D --> E["Survives terminal close<br/><small>no SIGHUP</small>"]
    C --> F["Child handle<br/>retained in DashMap"]
    F --> G["stop() / reaper<br/>still work"]

    class P parent
    class C child
    class D detached
    class E detached
    class F fork
    class G fork

Example

#![allow(unused)]
fn main() {
use process_manager::{ProcessConfig, ProcessManager, StdioConfig};

let manager = ProcessManager::new();
let config = ProcessConfig::builder()
    .command("my-daemon".to_string())
    .forked(true)
    .terminate_on_exit(true)
    .stdin(StdioConfig::Null)
    .stdout(StdioConfig::Null)
    .stderr(StdioConfig::Null)
    .build();

let id = manager.start("daemon", &config)?;
}

When to Use forked

• Daemons - Processes that should run independently of the parent’s terminal session
• Terminal applications - Processes that should not receive SIGHUP when the parent terminal closes
• Long-running services - Processes that outlive the parent and should not be tied to the parent’s session

When NOT to Use forked

• Compositor clients - Wayland clients should share the compositor’s session
• Short-lived commands - No need to detach processes that finish quickly
• Processes you want to receive terminal signals - setsid() detaches from the terminal, so terminal-generated signals (Ctrl+C, SIGHUP) won’t reach the child