From d1a7515f428e5b496a38cea6a887dd27dd9f1298 Mon Sep 17 00:00:00 2001
From: Johannes Matheis <jomat@jmt.gr>
Date: Thu, 8 Apr 2021 12:08:03 +0000
Subject: [PATCH] use flock for stale lock file handling

---
 dehydrated | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/dehydrated b/dehydrated
index 27f930f6..70e9ca43 100755
--- a/dehydrated
+++ b/dehydrated
@@ -536,7 +536,9 @@ init_system() {
   if [[ -n "${LOCKFILE}" ]]; then
     LOCKDIR="$(dirname "${LOCKFILE}")"
     [[ -w "${LOCKDIR}" ]] || _exiterr "Directory ${LOCKDIR} for LOCKFILE ${LOCKFILE} is not writable, aborting."
-    ( set -C; date > "${LOCKFILE}" ) 2>/dev/null || _exiterr "Lock file '${LOCKFILE}' present, aborting."
+    exec 100>>"${LOCKFILE}"
+    flock -n 100 || _exiterr "Lock file '${LOCKFILE}' is locked, aborting."
+    date >"${LOCKFILE}"  # for backward compability. Unreliable, since $LOCKFILE can exist after crash/SIGKILL
     remove_lock() { rm -f "${LOCKFILE}"; }
     trap 'remove_lock' EXIT
   fi