diff --git a/lib/AbstractException.php b/lib/AbstractException.php
index 26f679e..968f9e7 100644
--- a/lib/AbstractException.php
+++ b/lib/AbstractException.php
@@ -109,6 +109,10 @@ abstract class AbstractException extends \Exception {
         "Service/Exception.pidUnreadable"             => 10805,
         "Service/Exception.pidUnwritable"             => 10806,
         "Service/Exception.pidUncreatable"            => 10807,
+        "Service/Exception.pidCorrupt"                => 10808,
+        "Service/Exception.pidDuplicate"              => 10809,
+        "Service/Exception.pidLocked"                 => 10810,
+        "Service/Exception.pidInaccessible"           => 10811,
     ];
 
     protected $symbol;
diff --git a/lib/Service/Daemon.php b/lib/Service/Daemon.php
index 3fd615f..e83a7e2 100644
--- a/lib/Service/Daemon.php
+++ b/lib/Service/Daemon.php
@@ -7,6 +7,8 @@ declare(strict_types=1);
 namespace JKingWeb\Arsse\Service;
 
 class Daemon {
+    protected const PID_PATTERN = "/^(?:[1-9]\d{0,77})*$/s"; // no more than 78 digits (256-bit unsigned integer), starting with a digit other than zero
+
     /** Daemonizes the process via the traditional sysvinit double-fork procedure
      * 
      * @codeCoverageIgnore
@@ -20,7 +22,7 @@ class Daemon {
         # Reset all signal handlers to their default. This is best done by iterating through the available signals up to the limit of _NSIG and resetting them to SIG_DFL.
         // We have not yet set any signal handlers, so this should be fine
         # Reset the signal mask using sigprocmask().
-        // Not possible to my knowledge
+        pcntl_sigprocmask(\SIG_SETMASK, []);
         # Sanitize the environment block, removing or resetting environment variables that might negatively impact daemon runtime.
         //Not necessary; we don't use the environment
         # Call fork(), to create a background process.
@@ -77,10 +79,12 @@ class Daemon {
     protected function checkPID(string $pidfile) {
         if (file_exists($pidfile)) {
             $pid = (string) @file_get_contents($pidfile);
-            if (preg_match("/^\d+$/s", $pid)) {
-                if ($this->processExists((int) $pid)) {
-                    throw new \Exception("Process already exists");
+            if (preg_match(static::PID_PATTERN, $pid)) {
+                if (strlen($pid) && $this->processExists((int) $pid)) {
+                    throw new Exception("pidDuplicate", ['pid' => $pid]);
                 }
+            } else {
+                throw new Exception("pidCorrupt", ['pidfile' => $pidfile]);
             }
         }
     }
@@ -89,11 +93,13 @@ class Daemon {
         if ($f = @fopen($pidfile, "c+")) {
             if (@flock($f, \LOCK_EX | \LOCK_NB)) {
                 // confirm that some other process didn't get in before us
-                $pid = fread($f, 100);
-                if (preg_match("/^\d+$/s", (string) $pid)) {
+                $pid = fread($f, 80);
+                if (preg_match(static::PID_PATTERN, (string) $pid)) {
                     if ($this->processExists((int) $pid)) {
-                        throw new \Exception("Process already exists");
+                        throw new Exception("pidDuplicate", ['pid' => $pid]);
                     }
+                } else {
+                    throw new Exception("pidCorrupt", ['pidfile' => $pidfile]);
                 }
                 // write the PID to the pidfile
                 rewind($f);
@@ -101,10 +107,10 @@ class Daemon {
                 fwrite($f, (string) posix_getpid());
                 fclose($f);
             } else {
-                throw new \Exception("Process already exists");
+                throw new Exception("pidLocked", ['pidfile' => $pidfile]);
             }
         } else {
-            throw new \Exception("Could not write to PID file");
+            throw new Exception("pidInaccessible", ['pidfile' => $pidfile]);
         }
     }