diff --git a/src/daemon.rs b/src/daemon.rs
index d52bf38..c1c4832 100644
--- a/src/daemon.rs
+++ b/src/daemon.rs
@@ -39,6 +39,20 @@ pub fn run(config_path: String) {
         let _ = nix::sys::signal::sigaction(nix::sys::signal::Signal::SIGINT, &sig_action);
     }
 
+    // Single-instance guard: fail if another daemon already holds the lock.
+    // This prevents two supervisors from double-starting the same services.
+    let _daemon_lock = match state::lock_daemon() {
+        Ok(f) => f,
+        Err(e) => {
+            eprintln!(
+                "error: another daemon is already running (lock {:?}): {}",
+                state::daemon_pid_path(),
+                e
+            );
+            return;
+        }
+    };
+
     // Write daemon PID
     let pid_path = state::daemon_pid_path();
     if let Err(e) = state::write_pid(&pid_path) {
@@ -185,6 +199,9 @@ fn spawn(name: &str, cfg: &ServiceConfig) -> Option<Proc> {
                     libc::_exit(1);
                 }
                 libc::prctl(libc::PR_SET_PDEATHSIG, libc::SIGTERM);
+                // Put the service in its own process group so we can kill the
+                // whole tree (sh + grandchildren) instead of leaking orphans.
+                libc::setpgid(0, 0);
                 Ok(())
             });
         }
@@ -246,9 +263,10 @@ fn stop(name: &str, procs: &mut HashMap<String, Proc>) {
         let _ = Command::new("sh").arg("-c").arg(&cmd).output();
     }
 
-    // signal
+    // signal the whole process group (pid negative) so sh and any
+    // grandchildren all get it — otherwise background/pipeline children leak
     let sig = crate::supervisor::parse_signal(&p.cfg.stop_signal);
-    let _ = nix::sys::signal::kill(nix::unistd::Pid::from_raw(pid as i32), sig);
+    let _ = nix::sys::signal::kill(nix::unistd::Pid::from_raw(-(pid as i32)), sig);
 
     // wait
     let deadline = std::time::Instant::now() + Duration::from_secs(p.cfg.timeout_stop);
@@ -262,7 +280,7 @@ fn stop(name: &str, procs: &mut HashMap<String, Proc>) {
     // force kill
     if let Ok(None) = procs.get_mut(name).unwrap().child.try_wait() {
         let _ = nix::sys::signal::kill(
-            nix::unistd::Pid::from_raw(pid as i32),
+            nix::unistd::Pid::from_raw(-(pid as i32)),
             nix::sys::signal::Signal::SIGKILL,
         );
         let _ = procs.get_mut(name).unwrap().child.wait();
@@ -298,6 +316,13 @@ fn check_children(procs: &mut HashMap<String, Proc>) {
 
             append_log(&log_path, &format!("O: exited with {}", code));
 
+            // Clean up anything still running in the dead service's process
+            // group (e.g. background/pipeline children of `sh -c`).
+            let _ = nix::sys::signal::kill(
+                nix::unistd::Pid::from_raw(-(p.pid as i32)),
+                nix::sys::signal::Signal::SIGKILL,
+            );
+
             if p.cfg.oneshot {
                 dead.push(name.clone());
                 continue;
diff --git a/src/state.rs b/src/state.rs
index a391741..e9fad36 100644
--- a/src/state.rs
+++ b/src/state.rs
@@ -1,3 +1,4 @@
+use std::os::unix::io::AsRawFd;
 use std::path::PathBuf;
 
 pub fn runtime_dir() -> PathBuf {
@@ -105,6 +106,25 @@ pub fn write_pid(path: &PathBuf) -> std::io::Result<()> {
     std::fs::write(path, format!("{}", std::process::id()))
 }
 
+/// Acquire an exclusive lock on the daemon pid file.
+/// Held for the lifetime of the returned `File`; a second daemon fails here.
+pub fn lock_daemon() -> std::io::Result<std::fs::File> {
+    let path = daemon_pid_path();
+    if let Some(parent) = path.parent() {
+        std::fs::create_dir_all(parent)?;
+    }
+    let f = std::fs::OpenOptions::new()
+        .create(true)
+        .read(true)
+        .write(true)
+        .open(&path)?;
+    let rc = unsafe { libc::flock(f.as_raw_fd(), libc::LOCK_EX | libc::LOCK_NB) };
+    if rc != 0 {
+        return Err(std::io::Error::last_os_error());
+    }
+    Ok(f)
+}
+
 pub fn is_enabled(name: &str) -> bool {
     enabled_path(name).exists()
 }