children die when rss dies via PR_SET_PDEATHSIG

sets SIGTERM death signal in each child before exec, so if the
daemon exits (even by crash/SIGKILL), all managed services receive
SIGTERM and terminate. adds libc dependency for prctl.

Cargo.lock

@@ -346,6 +346,7 @@ version = "0.1.0"
 dependencies = [
  "chrono",
  "clap",
+ "libc",
  "nix",
  "serde",
  "toml",

Cargo.toml

@@ -9,3 +9,4 @@ serde = { version = "1", features = ["derive"] }
 toml = "0.8"
 chrono = "0.4"
 nix = { version = "0.29", default-features = false, features = ["signal", "fs"] }
+libc = "0.2"

src/daemon.rs

@@ -3,6 +3,7 @@ use std::fs;
 use std::io::{BufRead, BufReader, Write};
 use std::os::unix::fs::PermissionsExt;
 use std::os::unix::net::{UnixListener, UnixStream};
+use std::os::unix::process::CommandExt;
 use std::process::{Child, Command, Stdio};
 use std::time::{Duration, SystemTime};
 use std::sync::atomic::{AtomicBool, Ordering};
@@ -165,20 +166,28 @@ fn spawn(name: &str, cfg: &ServiceConfig) -> Option<Proc> {
     let log_path = log_path.to_string_lossy().to_string();
 
     let cmd = cfg.resolve_command(name, &log_path);
-    let mut child = match Command::new("sh")
-        .arg("-c")
-        .arg(&cmd)
-        .current_dir(&cfg.workdir)
-        .envs(&cfg.env)
-        .stdout(Stdio::piped())
-        .stderr(Stdio::piped())
-        .stdin(Stdio::null())
-        .spawn()
-    {
-        Ok(c) => c,
-        Err(e) => {
-            append_log(&log_path, &format!("E: spawn failed: {}", e));
-            return None;
+    let mut child = {
+        let mut sh = Command::new("sh");
+        sh.arg("-c")
+            .arg(&cmd)
+            .current_dir(&cfg.workdir)
+            .envs(&cfg.env)
+            .stdout(Stdio::piped())
+            .stderr(Stdio::piped())
+            .stdin(Stdio::null());
+        // SAFETY: pre_exec runs in the child after fork; minimal ops only
+        unsafe {
+            sh.pre_exec(|| {
+                libc::prctl(libc::PR_SET_PDEATHSIG, libc::SIGTERM);
+                Ok(())
+            });
+        }
+        match sh.spawn() {
+            Ok(c) => c,
+            Err(e) => {
+                append_log(&log_path, &format!("E: spawn failed: {}", e));
+                return None;
+            }
         }
     };