diff --git a/ChangeLog b/ChangeLog
index 4d184055d28..456ae4978f7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -39,7 +39,9 @@ For users:
        credit available.
 - New: Can use variables into the free text on PDF (__TOTAL_TTC_, __TOTAL_VAT...)
 - New: Increase page loading speed (all changes reported by Google PageSpeed
-       tool has been added). 
+       tool has been added).
+- New: Add support of constant MAIN_ONLY_LOGIN_ALLOWED to allow to lock all
+       access to any users axcept the one defined in constant. 
 - Fix: "Now" link works when date popup is not used.
 - Fix: Debug seriously the email notification module.
 - Fix: Error Call to a member function trans when refusing a supplier order.
diff --git a/htdocs/core/conf.class.php b/htdocs/core/conf.class.php
index 7e2d6c7a328..242b6114462 100644
--- a/htdocs/core/conf.class.php
+++ b/htdocs/core/conf.class.php
@@ -36,7 +36,7 @@
  */
 class Conf
 {
-    /** \public */
+	/** \public */
 	//! Object with database handler
 	var $db;
 	//! To store properties found in conf file
@@ -71,10 +71,10 @@ class Conf
 
 
 	/**
-	*      \brief      Load setup values into conf object
-	*      \param      $db			    Handler d'acces base
-	*      \return     int         		< 0 if KO, >= 0 if OK
-	*/
+	 *      \brief      Load setup values into conf object (read llx_const)
+	 *      \param      $db			    Handler d'acces base
+	 *      \return     int         		< 0 if KO, >= 0 if OK
+	 */
 	function setValues($db)
 	{
 		dol_syslog("Conf::setValues");
@@ -312,7 +312,7 @@ class Conf
 		$this->compta->mode = 'RECETTES-DEPENSES';  // By default
 		if (isset($this->global->COMPTA_MODE)) {
 			// Peut etre 'RECETTES-DEPENSES' ou 'CREANCES-DETTES'
-		    $this->compta->mode = $this->global->COMPTA_MODE;
+			$this->compta->mode = $this->global->COMPTA_MODE;
 		}
 
 		// $this->defaulttx
@@ -344,17 +344,17 @@ class Conf
 			$this->email_from = $this->global->MAIN_MAIL_EMAIL_FROM;
 		}
 		// $this->notification->email_from = email pour envoi par Dolibarr des notifications
-	    $this->notification->email_from=$this->email_from;
+		$this->notification->email_from=$this->email_from;
 		if (! empty($this->global->NOTIFICATION_EMAIL_FROM))
 		{
-		    $this->notification->email_from=$this->global->NOTIFICATION_EMAIL_FROM;
+			$this->notification->email_from=$this->global->NOTIFICATION_EMAIL_FROM;
 		}
 
 		// $this->mailing->email_from = email pour envoi par Dolibarr des mailings
 		$this->mailing->email_from=$this->email_from;;
 		if (! empty($this->global->MAILING_EMAIL_FROM))
 		{
-		    $this->mailing->email_from=$this->global->MAILING_EMAIL_FROM;
+			$this->mailing->email_from=$this->global->MAILING_EMAIL_FROM;
 		}
 
 		// Defini MAIN_GRAPH_LIBRARY
diff --git a/htdocs/langs/en_US/main.lang b/htdocs/langs/en_US/main.lang
index 44ec15bff23..082cb8acd66 100644
--- a/htdocs/langs/en_US/main.lang
+++ b/htdocs/langs/en_US/main.lang
@@ -527,7 +527,7 @@ PDFMerge=PDF Merge
 Merge=Merge
 PrintContentArea=Show page to print main content area
 NoMenu=No sub-menu
-WarningYouAreInMaintenanceMode=Warning, you are in a maintenance mode, so only login <b>%s</b> is allowed to connect.
+WarningYouAreInMaintenanceMode=Warning, you are in a maintenance mode, so only login <b>%s</b> is allowed to use application at the moment.
 # Week day
 Day1=Monday
 Day2=Tuesday
diff --git a/htdocs/langs/fr_FR/main.lang b/htdocs/langs/fr_FR/main.lang
index 8421b0e3aa9..37402a02fc3 100644
--- a/htdocs/langs/fr_FR/main.lang
+++ b/htdocs/langs/fr_FR/main.lang
@@ -526,7 +526,7 @@ PDFMerge=Fusion PDF
 Merge=Fusion
 PrintContentArea=Afficher page d'impression de la zone centrale
 NoMenu=Aucun sous-menu
-WarningYouAreInMaintenanceMode=Attention, vous êtes en mode maintenance, aussi seul le login <b>%s</b> est autorisé à se connecter.
+WarningYouAreInMaintenanceMode=Attention, vous êtes en mode maintenance, aussi seul le login <b>%s</b> est autorisé à utiliser l'application en ce moment.
 # Week day
 Day1=Lundi
 Day2=Mardi
diff --git a/htdocs/main.inc.php b/htdocs/main.inc.php
index d3806c5dd17..382c1fc2507 100644
--- a/htdocs/main.inc.php
+++ b/htdocs/main.inc.php
@@ -1097,6 +1097,7 @@ function left_menu($menu_array, $helppagename='', $moresearchform='')
 	print "\n";
 	print '<div class="fiche"> <!-- begin main area -->'."\n";
 
+	if (! empty($conf->global->MAIN_ONLY_LOGIN_ALLOWED)) print info_admin($langs->trans("WarningYouAreInMaintenanceMode",$conf->global->MAIN_ONLY_LOGIN_ALLOWED));
 }
 
 
diff --git a/htdocs/master.inc.php b/htdocs/master.inc.php
index 1fa0d2f4ab4..61891041020 100644
--- a/htdocs/master.inc.php
+++ b/htdocs/master.inc.php
@@ -58,9 +58,8 @@ error_reporting(E_ALL ^ E_NOTICE);
 
 // Include configuration
 $result=@include_once("conf/conf.php");
-if (! $result && $_SERVER["GATEWAY_INTERFACE"])
+if (! $result && $_SERVER["GATEWAY_INTERFACE"])	// If install not done and we are in a web session
 {
-	// If install not done and we are in a web session
 	header("Location: install/index.php");
 	exit;
 }
@@ -140,7 +139,7 @@ if (empty($dolibarr_main_db_collation)) $dolibarr_main_db_collation='latin1_swed
 $conf->db->dolibarr_main_db_collation=$dolibarr_main_db_collation;
 if (empty($dolibarr_main_db_encryption)) $dolibarr_main_db_encryption=0;
 $conf->db->dolibarr_main_db_encryption = $dolibarr_main_db_encryption;
-if (empty($dolibarr_main_db_cryptkey)) $dolibarr_main_db_cryptkey=''; // TODO la cle devra ne doit pas etre stockee sur le serveur
+if (empty($dolibarr_main_db_cryptkey)) $dolibarr_main_db_cryptkey='';
 $conf->db->dolibarr_main_db_cryptkey = $dolibarr_main_db_cryptkey;
 // Identifiant autres
 $conf->file->main_authentication = empty($dolibarr_main_authentication)?'':$dolibarr_main_authentication;
@@ -177,6 +176,7 @@ if (isset($_SERVER["HTTP_USER_AGENT"]))
 	elseif (eregi('chrome',$_SERVER["HTTP_USER_AGENT"]))    $conf->browser->name='chrome';
 	elseif (eregi('opera',$_SERVER["HTTP_USER_AGENT"]))     $conf->browser->name='opera';
 	elseif (eregi('msie',$_SERVER["HTTP_USER_AGENT"]))      $conf->browser->name='ie';
+	else $conf->browser->name='unknown';
 	if (in_array($conf->browser->name,array('firefox','iceweasel'))) $conf->browser->firefox=1;
 }
 
@@ -209,7 +209,7 @@ if (! defined('NOREQUIREDB'))
 }
 // Now database connexion is known, so we can forget password
 //$dolibarr_main_db_pass=''; 	// Comment this because this constant is used in a lot of pages
-$conf->db->pass='';				// This is to avoid password to be shown in dump
+$conf->db->pass='';				// This is to avoid password to be shown in memory/swap dump
 
 /*
  * Creation objet $user
@@ -254,7 +254,40 @@ if (! defined('NOREQUIREDB'))
 		}
 	}
 
-	$conf->setValues($db);
+	$conf->setValues($db);	// Here we read database (llx_const table) and define $conf->global->XXX var.
+}
+
+// If software has been locked. Only login $conf->global->MAIN_ONLY_LOGIN_ALLOWED is allowed.
+if (! empty($conf->global->MAIN_ONLY_LOGIN_ALLOWED))
+{
+	/*print '$_SERVER["GATEWAY_INTERFACE"]='.$_SERVER["GATEWAY_INTERFACE"].'<br>';
+	print 'session_id()='.session_id().'<br>';
+	print '$_SESSION["dol_login"]='.$_SESSION["dol_login"].'<br>';
+	print '$conf->global->MAIN_ONLY_LOGIN_ALLOWED='.$conf->global->MAIN_ONLY_LOGIN_ALLOWED.'<br>';
+	exit;*/
+	$ok=0;
+	if ((! session_id() || ! isset($_SESSION["dol_login"])) && ! isset($_POST["username"]) && ! empty($_SERVER["GATEWAY_INTERFACE"])) $ok=1;	// We let working pages if not logged and inside a web browser (login form, to allow login by admin)
+	elseif (isset($_POST["username"]) && $_POST["username"] == $conf->global->MAIN_ONLY_LOGIN_ALLOWED) $ok=1;				// We let working pages that is a login submission (login submit, to allow login by admin)
+	elseif (defined('NOREQUIREDB'))   $ok=1;				// We let working pages that don't need database access (xxx.css.php)
+	elseif (defined('EVEN_IF_ONLY_LOGIN_ALLOWED')) $ok=1;	// We let working pages that ask to work even if only login enabled (logout.php)
+	elseif (session_id() && isset($_SESSION["dol_login"]) && $_SESSION["dol_login"] == $conf->global->MAIN_ONLY_LOGIN_ALLOWED) $ok=1;	// We let working if user is allowed admin
+	if (! $ok)
+	{
+		if (session_id() && isset($_SESSION["dol_login"]) && $_SESSION["dol_login"] != $conf->global->MAIN_ONLY_LOGIN_ALLOWED)
+		{
+			print 'Sorry, your application is offline.'."\n";
+			print 'You are logged with user "'.$_SESSION["dol_login"].'" and only administrator user "'.$conf->global->MAIN_ONLY_LOGIN_ALLOWED.'" is allowed to connect for the moment.'."\n";
+			$nexturl=DOL_URL_ROOT.'/user/logout.php';
+			print 'Please try later or <a href="'.$nexturl.'">click here to disconnect and change login user</a>...'."\n";
+		}
+		else
+		{
+			print 'Sorry, your application is offline. Only administrator user "'.$conf->global->MAIN_ONLY_LOGIN_ALLOWED.'" is allowed to connect for the moment.'."\n";
+			$nexturl=DOL_URL_ROOT.'/';
+			print 'Please try later or <a href="'.$nexturl.'">click here to change login user</a>...'."\n";
+		}
+		exit;
+	}
 }
 
 /*