diff --git a/README.md b/README.md
index 4054d7c..e09ff0d 100644
--- a/README.md
+++ b/README.md
@@ -14,9 +14,10 @@ Sends a WOL packet to the specified host on website request and redirects to the
 
 ## `config.json` definition
 
-| Key        | Description                                                                      |
-|------------|----------------------------------------------------------------------------------|
-| `host.mac` | The MAC address of the adapter that you want to wake (get it with `ip addr`)     |
-| `host.ip`  | The IP address of the device you want to wake (only used for routing)            |
-| `timeout`  | The timeout between refreshes in the browser (`0` disables automatic refreshing) |
-| `details`  | Show details to the client (e.g. try count, destination url, etc.)               |
+| Key        | Description                                                                                 |
+|------------|---------------------------------------------------------------------------------------------|
+| `host.mac` | The MAC address of the adapter that you want to wake (get it with `ip addr`)                |
+| `host.ip`  | The IP address of the device you want to wake (only used for ICMP ping)                     |
+| `timeout`  | The timeout between refreshes in the browser (`0` disables automatic refreshing)            |
+| `details`  | Show details to the client (e.g. try count, destination url, etc.)                          |
+| `log`      | When `true` write log messages via the `error_log` function for debugging output (optional) |
diff --git a/config.sample.json b/config.sample.json
index cd53924..3dea0b1 100644
--- a/config.sample.json
+++ b/config.sample.json
@@ -4,5 +4,6 @@
     "ip": "192.168.0.2"
   },
   "timeout": 5,
-  "details": false
+  "details": false,
+  "log": false
 }
\ No newline at end of file
diff --git a/lib.php b/lib.php
index 3edf984..68dbd05 100644
--- a/lib.php
+++ b/lib.php
@@ -7,13 +7,46 @@
 const SESSION_PARAM_TRY_COUNT = "count";
 
 if (!file_exists(CONFIG_PATH)) {
-    die("Configuration file doesn't exist. Please create JSON file at " . CONFIG_PATH . " and try again!");
+    die("Configuration file doesn't exist. Please create JSON file at \"" . CONFIG_PATH . "\" and try again.");
 }
 
 $config = json_decode(file_get_contents(CONFIG_PATH));
+$log_enabled = $config->{"log"} ?? false;
+
+/// logging section
+
+function notice(string $message, string $scope = null): void {
+    global $log_enabled;
+    if (!$log_enabled) return;
+    $scope = isset($scope) ? " [" . $scope . "]" : "";
+    error_log("notice" . $scope . ": " . $message . "\n");
+}
+
+function warn(string $message, string $scope = null): void {
+    global $log_enabled;
+    if (!$log_enabled) return;
+    $scope = isset($scope) ? " [" . $scope . "]" : "";
+    error_log("warn" . $scope . ": " . $message . "\n");
+}
+
+function error(string $message, string $scope = null): void {
+    global $log_enabled;
+    if (!$log_enabled) return;
+    $scope = isset($scope) ? " [" . $scope . "]" : "";
+    error_log("error" . $scope . ": " . $message . "\n");
+}
 
 /// command section
 
+/**
+ * Same as {@link exec()} but additionally logs everything to the error log.
+ */
+function execute_command(string $command, array &$output, int &$result_code, string $scope = null) {
+    $result = exec($command, $output, $result_code);
+    notice("executed: " . $command . ", got: " . $output[0] . ", rc: " . $result_code, $scope);
+    return $result;
+}
+
 /**
  * Checks if a given command (UNIX binary) is in the PATH environment.
  *
@@ -23,8 +56,7 @@ function command_exists(string $command): bool
 {
     $output = [];
     $result_code = 0;
-    $cmd = "command -v " . $command;
-    exec($cmd, $output, $result_code);
+    execute_command("command -v " . escapeshellarg($command), $output, $result_code, "command_exists");
     return $result_code == 0;
 }
 
@@ -38,13 +70,11 @@ function get_command_path(string $command): string
 {
     $output = [];
     $result_code = 0;
-    $cmd = "command -v " . $command;
-    exec($cmd, $output, $result_code);
+    execute_command("command -v " . escapeshellarg($command), $output, $result_code, "get_command_path");
 
     if ($result_code > 0) {
         die("Requested command " . $command . " doesn't exist. Please install the required package and try again.");
     }
-
     return $output[0];
 }
 
@@ -65,8 +95,7 @@ function is_up(): bool
     $output = [];
     $result_code = 0;
     $cmd = get_command_path("ping") . " -q -c 1 -w 1 " . $config->{"host"}->{"ip"};
-    exec($cmd, $output, $result_code);
-
+    execute_command($cmd, $output, $result_code, "is_up");
     return $result_code == 0;
 }
 
@@ -79,23 +108,19 @@ function wake(): bool
 {
     global $config;
 
-    // send one WOL packet to the host
+    // send one WoL packet to the host
     if (command_exists("wol")) {
-        $wol_command = sprintf(get_command_path("wol") . " -i \"%s\" \"%s\"",
-            $config->{"host"}->{"ip"},
-            $config->{"host"}->{"mac"}
-        );
+        notice("Found \"wol\" as WoL binary", "wake");
+        $wol_command = get_command_path("wol") . " " . escapeshellarg($config->{"host"}->{"mac"});
     } else if (command_exists("wakeonlan")) {
-        $wol_command = sprintf(get_command_path("wakeonlan") . " -i \"%s\" \"%s\"",
-            $config->{"host"}->{"ip"},
-            $config->{"host"}->{"mac"}
-        );
+        notice("Found \"wakeonlan\" as WoL binary", "wake");
+        $wol_command = get_command_path("wakeonlan") . " " . escapeshellarg($config->{"host"}->{"mac"});
     } else {
-        die("No wakeonlan binaries found. Please install \"wakeonlan\" or \"wol\" package.");
+        die("No WoL binaries found. Please install \"wakeonlan\" or \"wol\" package.");
     }
 
     $output = [];
     $result_code = 0;
-    exec($wol_command, $output, $result_code);
+    execute_command($wol_command, $output, $result_code, "wake");
     return $result_code == 0;
 }