Use the setupVars.conf option TEMPERATUREUNIT, plus slight rearrangement of settings page

api.php

@@ -75,6 +75,17 @@
     $data = array_merge($data, $current);
     $data = array_merge($data, $latest);
     $data = array_merge($data, $branches);
+} elseif (isset($_GET['setTempUnit'])) {
+    $unit = strtolower($_GET['setTempUnit']);
+    if ($unit == 'c' || $unit == 'f' || $unit == 'k') {
+        pihole_execute('-a -'.$unit);
+        $result = 'success';
+    } else {
+        // invalid unit
+        $result = 'error';
+    }
+
+    $data = array_merge($data, array('result' => $result));
 } elseif (isset($_GET['list'])) {
     if (!$auth) {
         exit('Not authorized!');

scripts/pi-hole/js/footer.js

@@ -160,10 +160,6 @@ function initCheckboxRadioStyle() {
 
 function initCPUtemp() {
   function setCPUtemp(unit) {
-    if (localStorage) {
-      localStorage.setItem("tempunit", tempunit);
-    }
-
     var temperature = parseFloat($("#rawtemp").text());
     var displaytemp = $("#tempdisplay");
     if (!isNaN(temperature)) {
@@ -185,10 +181,30 @@ function initCPUtemp() {
     }
   }
 
-  // Read from local storage, initialize if needed
-  var tempunit = localStorage ? localStorage.getItem("tempunit") : null;
-  if (tempunit === null) {
-    tempunit = "C";
+  function setSetupvarsTempUnit(unit, showmsg = true) {
+    var token = encodeURIComponent($("#token").text());
+    $.getJSON("api.php?setTempUnit=" + unit + "&token=" + token, function (data) {
+      if (showmsg === true) {
+        if ("result" in data && data.result === "success") {
+          utils.showAlert("success", "", "Temperature unit set to " + unit, "");
+        } else {
+          utils.showAlert("error", "", "", "Temperature unit not set");
+        }
+      }
+    });
+  }
+
+  // Read the temperature unit from HTML code
+  var tempunit = $("#tempunit").text();
+  if (!tempunit) {
+    // if no value was set in setupVars.conf, tries to retrieve the old config from localstorage
+    tempunit = localStorage ? localStorage.getItem("tempunit") : null;
+    if (tempunit === null) {
+      tempunit = "C";
+    } else {
+      // if some value was found on localstorage, set the value in setupVars.conf
+      setSetupvarsTempUnit(tempunit, false);
+    }
   }
 
   setCPUtemp(tempunit);
@@ -200,6 +216,9 @@ function initCPUtemp() {
     tempunitSelector.on("change", function () {
       tempunit = $(this).val();
       setCPUtemp(tempunit);
+
+      // store the selected value on setupVars.conf
+      setSetupvarsTempUnit(tempunit);
     });
   }
 }

scripts/pi-hole/php/header_authenticated.php

@@ -98,7 +98,23 @@ function getTemperature()
         $limit = null;
     }
 
-    return array($celsius, $limit);
+    // Get user-defined temperature limit if set
+    if (isset($setupVars['TEMPERATUREUNIT'])) {
+        switch (strtoupper($setupVars['TEMPERATUREUNIT'])) {
+            case 'F':
+            case 'K':
+                $unit = strtoupper($setupVars['TEMPERATUREUNIT']);
+                break;
+
+            default:
+                $unit = 'C';
+        }
+    } else {
+        // no value is set in setupVars.conf
+        $unit = '';
+    }
+
+    return array($celsius, $limit, $unit);
 }
 
 check_cors();
@@ -113,7 +129,7 @@ function getTemperature()
 $maxlifetime = ini_get('session.gc_maxlifetime');
 
 // Get temperature
-list($celsius, $temperaturelimit) = getTemperature();
+list($celsius, $temperaturelimit, $temperatureunit) = getTemperature();
 
 // Get CPU load
 $loaddata = sys_getloadavg();

scripts/pi-hole/php/sidebar.php

@@ -57,6 +57,7 @@
                         }
                         echo '<span id="temperature"><i class="fa fa-w fa-fire '.$tempcolor.'" style="width: 1em !important"></i> ';
                         echo 'Temp:&nbsp;<span id="rawtemp" hidden>'.$celsius.'</span>';
+                        echo '<span id="tempunit" hidden>'.$temperatureunit.'</span>';
                         echo '<span id="tempdisplay"></span></span>';
                     }
                     ?>