Handle stale pid file for crashing daemons

doc/ChangeLog.md

@@ -3,6 +3,31 @@ Change Log
 
 All relevant changes are documented in this file.
 
+[Unreleased]
+------------
+
+### Changes
+
+- Restart log now spells out the signal name and flags core dumps,
+  e.g. `killed by SIGKILL` or `killed by SIGSEGV, core dumped`, in
+  place of the bare numeric `by signal: N`.  Gives operators a much
+  stronger breadcrumb when a daemon dies unexpectedly
+
+### Fixes
+
+- Remove stale daemon-owned (`pid:!`) pidfiles after unclean exits.
+  When a daemon dies via SIGKILL/OOM/segfault, or exits early during
+  startup, its pidfile lingers and can prevent the next instance from
+  starting -- `dbus-daemon` for example refuses to start when its
+  pidfile already exists, so Finit's restart loop gives up.  Finit now
+  drops the file when it still names the just-reaped PID and that PID
+  is no longer alive (the liveness check guards against PID reuse).
+  This is a controlled exception to the long-standing rule that Finit
+  does not touch service-owned pidfiles
+- Fix misspelled `SIGUNKOWN` returned by `sig_name()` for unknown
+  signal numbers, now spelled correctly as `SIGUNKNOWN`.  Surfaced by
+  the new restart log above
+
 [4.17][] - 2026-04-28
 ---------------------
 

doc/config/services.md

@@ -31,6 +31,14 @@ basename of the binary to guess the PID file to watch for the PID:
 `/var/run/ntpd.pid`.  If Finit guesses wrong, you have to submit the
 full `pid:!/path/to/file.pid`.
 
+With `pid:!/path`, the file belongs to the service: Finit reads it
+but does not create or remove it.  The one exception is *stale*
+cleanup — if the service dies without removing its own pidfile
+(SIGKILL, OOM, segfault), and the file still names the just-reaped
+PID, Finit removes it before the next retry.  This prevents daemons
+that refuse to start on an existing pidfile (e.g. `dbus-daemon`)
+from getting stuck in a crash-restart loop.
+
 **Example:**
 
 In the case of `ospfd` (below), we omit the `-d` flag (daemonize) to

src/pid.c

@@ -201,7 +201,10 @@ int pid_file_set(svc_t *svc, char *file, int not)
  * pid:!foo          --> !/run/foo.pid
  * pid:!/run/foo.pid --> !/run/foo.pid
  *
- * Note, nothing is created or removed by Finit in this latter form.
+ * Nothing is created or removed by Finit in this latter form, with one
+ * exception: a verifiably stale pidfile (still names the just-reaped
+ * PID, and that PID is no longer alive) is removed so the next instance
+ * can start.  See service_clean_pidfile() in src/service.c.
  */
 int pid_file_parse(svc_t *svc, char *arg)
 {

src/service.c

@@ -1120,6 +1120,35 @@ static void service_notify_stop(svc_t *svc)
 	}
 }
 
+/*
+ * Drop a daemon-owned (pid:!) pidfile if it still names the just-reaped
+ * PID and that PID is gone.  The liveness check guards against reuse.
+ */
+static void service_clean_pidfile(svc_t *svc, pid_t reaped)
+{
+	pid_t pid;
+	char *fn;
+
+	if (reaped <= 1)
+		return;
+
+	fn = pid_file(svc);
+	if (!fn)
+		return;
+
+	pid = pid_file_read(fn);
+	if (pid != reaped || pid_alive(pid))
+		return;
+
+	if (remove(fn) && errno != ENOENT) {
+		logit(LOG_CRIT, "Failed removing stale service %s pidfile %s",
+		      svc_ident(svc, NULL, 0), fn);
+		return;
+	}
+
+	dbg("Removed stale service %s pidfile %s", svc_ident(svc, NULL, 0), fn);
+}
+
 /*
  * Clean up any lingering state from dead/killed services
  */
@@ -1137,6 +1166,8 @@ static void service_cleanup(svc_t *svc)
 		if (remove(fn) && errno != ENOENT)
 			logit(LOG_CRIT, "Failed removing service %s pidfile %s",
 			      svc_ident(svc, NULL, 0), fn);
+	} else if (svc->pidfile[0] == '!') {
+		service_clean_pidfile(svc, svc->pid);
 	}
 
 	/*
@@ -2405,7 +2436,10 @@ void service_monitor(pid_t lost, int status)
 	if (svc_is_forking(svc)) {
 		/* Likely start script exiting */
 		if (svc_is_starting(svc)) {
-			svc->pid = 0;	/* Expect no more activity from this one */
+			/* Daemon died before clearing 'starting'; drop any stale pidfile. */
+			service_clean_pidfile(svc, lost);
+			svc->oldpid = lost;	/* So service_retry() logs the real PID */
+			svc->pid = 0;		/* Expect no more activity from this one */
 			goto cont;
 		}
 
@@ -2794,13 +2828,18 @@ static void service_retry(svc_t *svc)
 	timeout = ((*restart_cnt) <= (svc->restart_max / 2)) ? 2000 : 5000;
 	/* If a longer timeout was specified in the conf, use that instead. */
 	svc->restart_tmo = max(svc->restart_tmo, timeout);
-	logit(LOG_CONSOLE|LOG_WARNING, "Service %s[%d] died (%s%d), restarting (retry in %d msec) (attempt: %d/%d)",
-	      svc_ident(svc, NULL, 0), svc->oldpid,
-	      WIFEXITED(svc->status) ? "with exit status: " : "by signal: ",
-	      WIFEXITED(svc->status) ? WEXITSTATUS(svc->status) : WTERMSIG(svc->status),
-	      svc->restart_tmo,
-	      *restart_cnt,
-	      svc->restart_max);
+	if (WIFEXITED(svc->status))
+		logit(LOG_CONSOLE|LOG_WARNING,
+		      "Service %s[%d] died (exit status: %d), restarting (retry in %d msec) (attempt: %d/%d)",
+		      svc_ident(svc, NULL, 0), svc->oldpid, WEXITSTATUS(svc->status),
+		      svc->restart_tmo, *restart_cnt, svc->restart_max);
+	else
+		logit(LOG_CONSOLE|LOG_WARNING,
+		      "Service %s[%d] died (killed by %s%s), restarting (retry in %d msec) (attempt: %d/%d)",
+		      svc_ident(svc, NULL, 0), svc->oldpid,
+		      sig_name(WTERMSIG(svc->status)),
+		      WCOREDUMP(svc->status) ? ", core dumped" : "",
+		      svc->restart_tmo, *restart_cnt, svc->restart_max);
 
 	svc_unblock(svc);
 	service_step(svc);

src/sig.c

@@ -630,7 +630,7 @@ const char *sig_name(int signo)
 			return signames[i].name;
 	}
 
-	return "SIGUNKOWN";
+	return "SIGUNKNOWN";
 }
 
 /*

test/Makefile.am

@@ -41,6 +41,7 @@ EXTRA_DIST		+= global-envs.sh
 EXTRA_DIST		+= initctl-status-subset.sh
 EXTRA_DIST		+= notify.sh
 EXTRA_DIST		+= pidfile.sh
+EXTRA_DIST		+= stale-pidfile.sh
 EXTRA_DIST		+= pre-post-serv.sh
 EXTRA_DIST		+= pre-fail.sh
 EXTRA_DIST		+= process-depends.sh
@@ -84,6 +85,7 @@ TESTS			+= global-envs.sh
 TESTS			+= initctl-status-subset.sh
 TESTS			+= notify.sh
 TESTS			+= pidfile.sh
+TESTS			+= stale-pidfile.sh
 TESTS			+= pre-post-serv.sh
 TESTS			+= pre-fail.sh
 TESTS			+= process-depends.sh

test/src/serv.c

@@ -34,6 +34,7 @@ volatile sig_atomic_t reloading = 1;
 volatile sig_atomic_t running   = 1;
 static char *ident = PROGNM;
 static char fn[80];
+static int  exclusive = 0;	/* -x: refuse to start if pidfile exists (dbus-style) */
 
 static void verify_env(char *arg)
 {
@@ -122,7 +123,7 @@ static void writefn(char *fn, int val)
 
 static int checkfn(char *fn)
 {
-	return !access(fn, R_OK);
+	return !access(fn, F_OK);
 }
 
 static void mine(char *fn)
@@ -133,12 +134,18 @@ static void mine(char *fn)
 
 static void pidfile(char *pidfn)
 {
+	static int once = 0;
+
 	if (!pidfn) {
 		if (fn[0] == 0)
 			snprintf(fn, sizeof(fn), "%s%s.pid", _PATH_VARRUN, ident);
 		pidfn = fn;
 	}
 
+	if (exclusive && !once && checkfn(pidfn))
+		errx(EX_SOFTWARE, "PID file %s exists, refusing to start", pidfn);
+	once = 1;
+
 	if (!checkfn(pidfn)) {
 		pid_t pid;
 
@@ -148,7 +155,7 @@ static void pidfile(char *pidfn)
 		atexit(cleanup);
 	} else {
 		inf("Touching PID file %s", pidfn);
-		utimensat(0, fn, NULL, 0);
+		utimensat(AT_FDCWD, pidfn, NULL, 0);
 	}
 }
 
@@ -182,6 +189,7 @@ static int usage(int rc)
 		" -p       Create PID file despite running in foreground\n"
 		" -P FILE  Create PID file using FILE\n"
 		" -r SVC   Call initctl to restart service SVC (self)\n"
+		" -x       Refuse to start if PID file already exists (dbus-style)\n"
 		"\n"
 		"By default this program daemonizes itself to the background, and,\n"
 		"when it's done setting up its signal handler(s), creates a PID file\n"
@@ -212,7 +220,7 @@ int main(int argc, char *argv[])
 	char cmd[80];
 	int c;
 
-	while ((c = getopt(argc, argv, "cCe:E:f:F:hi:nN:pP:r:")) != EOF) {
+	while ((c = getopt(argc, argv, "cCe:E:f:F:hi:nN:pP:r:x")) != EOF) {
 		switch (c) {
 		case 'c':
 			do_crash = 1;
@@ -249,12 +257,17 @@ int main(int argc, char *argv[])
 			break;
 		case 'P':
 			pidfn = optarg;
+			if ((size_t)snprintf(fn, sizeof(fn), "%s", optarg) >= sizeof(fn))
+				errx(EX_USAGE, "-P path too long (max %zu)", sizeof(fn) - 1);
 			do_pidfile++;
 			break;
 		case 'r':
 			snprintf(cmd, sizeof(cmd), "initctl restart %s", optarg);
 			do_restart = 1;
 			break;
+		case 'x':
+			exclusive = 1;
+			break;
 		default:
 			return usage(1);
 		}

test/stale-pidfile.sh

@@ -0,0 +1,38 @@
+#!/bin/sh
+# Regression: Finit must remove a daemon-owned (pid:!) stale pidfile
+# left behind by an unclean exit (SIGKILL), so the next instance can
+# start.  Simulates the dbus-daemon pattern: 'serv -x' refuses to
+# start if its pidfile already exists.
+
+set -eu
+
+TEST_DIR=$(dirname "$0")
+PIDFN="/run/serv.pid"
+
+test_teardown()
+{
+    say "Running test teardown."
+    run "rm -f $FINIT_CONF $PIDFN"
+}
+
+# shellcheck source=/dev/null
+. "$TEST_DIR/lib/setup.sh"
+
+say "Add service stanza '$FINIT_CONF' with pid:!$PIDFN"
+run "echo 'service pid:!$PIDFN serv -np -P $PIDFN -x' > $FINIT_CONF"
+run "initctl reload"
+
+retry "assert_num_children 1 serv"
+assert_is_pidfile "serv" "$PIDFN"
+
+PID=$(texec cat "$PIDFN")
+say "SIGKILL serv ($PID) -- leaves stale pidfile"
+run "kill -9 $PID"
+
+# Without the fix, 'serv -x' refuses to start on each retry until
+# Finit hits restart_max and marks the service crashed.  With the fix
+# Finit removes the stale pidfile and the next instance comes up.
+retry "assert_pidiff serv $PID"
+retry "assert_num_children 1 serv"
+
+sep