diff --git a/bin/qasim-gui.rb b/bin/qasim-gui.rb
index 04f2f3e..5867c3d 100755
--- a/bin/qasim-gui.rb
+++ b/bin/qasim-gui.rb
@@ -7,6 +7,7 @@ $VERBOSE = true
 
 require 'pp'
 require 'set'
+require 'fcntl'
 
 QASIM_INCLUDE_DIR = "."
 $:.push QASIM_INCLUDE_DIR
@@ -143,13 +144,13 @@ module Qasim
 			@context_menu = Qt::Menu.new
 
 			act_pref = Qt::Action.new _('&Preferences'), @context_menu
-			act_pref.setIcon(  Qt::Icon::fromTheme("configure") )
+			act_pref.setIcon(  Qt::Icon::fromTheme("configure") ) rescue nil
 			act_pref.setIconVisibleInMenu true
 			act_pref.setEnabled false
 			@context_menu.addAction act_pref;
 
 			act_about = Qt::Action.new '&About', @context_menu
-			act_about.setIcon( Qt::Icon::fromTheme("help-about") )
+			act_about.setIcon( Qt::Icon::fromTheme("help-about") ) rescue nil
 			act_about.setIconVisibleInMenu true
 			act_about.setEnabled false
 			@context_menu.addAction act_about;
@@ -157,7 +158,7 @@ module Qasim
 			@context_menu.addSeparator
 
 			act_quit = Qt::Action.new _('Quit'), @context_menu
-			act_quit.setIcon(  Qt::Icon::fromTheme("application-exit") )
+			act_quit.setIcon(  Qt::Icon::fromTheme("application-exit") ) rescue nil
 			act_quit.setIconVisibleInMenu true
 			act_quit.connect(SIGNAL(:triggered)) { @app.quit }
 			@context_menu.addAction act_quit
@@ -209,7 +210,25 @@ module Qasim
 		#
 		#
 		def run
+			# create lock
+			have_lock = true
+
+			FileUtils.mkdir_p APP_CONFIG_DIR unless File.exist? APP_CONFIG_DIR
+			lockfname = File.join APP_CONFIG_DIR, "lock"
+			fd = IO::sysopen( lockfname,
+							 Fcntl::O_WRONLY | Fcntl::O_EXCL | Fcntl::O_CREAT)
+			f = IO.open(fd)
+			f.syswrite( "Process.pid\n" )
+			f.close
 			@app.exec
+		rescue Errno::EEXIST => e
+			warn "error: Another instance of %s is already running." % APP_NAME
+			exit 1
+		ensure
+			masterpid = File.read(lockfname).strip
+			if masterpid == Process.pid then
+				FileUtils.rm lockfname
+			end
 		end
 
 
diff --git a/debian/changelog b/debian/changelog
index b30213b..7c754f2 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,10 @@
+qasim (0.1.6) unstable; urgency=low
+
+  * qasim-gui: handle QIcon::fromTheme NoMethodError exception when needed.
+  * qasim-gui: added single instance lock.
+
+ -- Glenn Y. Rolland <glenux@glenux.net>  Wed, 07 Sep 2011 01:08:48 +0200
+
 qasim (0.1.5) unstable; urgency=low
 
   * map: Added missing require for fileutils. 
diff --git a/qasim/config.rb b/qasim/config.rb
index 647906b..171addb 100644
--- a/qasim/config.rb
+++ b/qasim/config.rb
@@ -20,27 +20,10 @@ module Qasim
 
 		def initialize
 
-			user = if ENV['USER'] then
-					   ENV['USER']
-				   else
-					   raise "Environment variable 'USER' is missing!"
-				   end
 
-			home_dir = if ENV['HOME'] then 
-						   ENV['HOME']
-					   else
-						   "/home/" + user
-					   end
+			@mnt_dir = File.join ENV['HOME'], "mnt"
 
-			xdg_dir = if ENV['XDG_CONFIG_HOME'] then
-						  ENV['XDG_CONFIG_HOME']
-					  else
-						  home_dir + '/.config'
-					  end
-
-			@mnt_dir = File.join home_dir, "mnt"
-
-			@config_dir = xdg_dir + '/sshfs-mapper'
+			@config_dir = APP_CONFIG_DIR
 			@config_file = nil
 			@maps = []
 			@initialize_enable = false
diff --git a/qasim/constants.rb b/qasim/constants.rb
index 0ffc237..fd21c64 100644
--- a/qasim/constants.rb
+++ b/qasim/constants.rb
@@ -1,6 +1,13 @@
 module Qasim
 	APP_ICON_PATH = File.join QASIM_INCLUDE_DIR, "icons"
-	APP_SYSCONFIG_DIR = "/etc/qasim/maps.d"
 	APP_NAME = "Qasim"
 	APP_VERSION = "0.1"
+
+	APP_SYSCONFIG_DIR = "/etc/qasim/maps.d"
+
+	APP_CONFIG_DIR = if ENV['XDG_CONFIG_HOME'] then
+						 File.join ENV['XDG_CONFIG_HOME'], 'qasim'
+					 else
+						 File.join ENV['HOME'], '.config', 'qasim'
+					 end
 end