ui: print a warning if XDG_SESSION_TYPE is not set

If XDG_SESSION_TYPE is not set there're no icons on the GUI.
More info: #999

ui/bin/opensnitch-ui

@@ -22,7 +22,6 @@
 #   along with OpenSnitch.  If not, see <http://www.gnu.org/licenses/>.
 
 from PyQt5 import QtWidgets, QtCore
-from PyQt5.QtCore import QCoreApplication as QC
 from PyQt5.QtNetwork import QLocalServer, QLocalSocket
 
 import sys
@@ -42,7 +41,7 @@ if dist_path not in sys.path:
 from opensnitch.service import UIService
 from opensnitch.config import Config
 from opensnitch.utils import Themes, Utils, Versions, Message
-from opensnitch.utils.xdg import xdg_opensnitch_dir
+from opensnitch.utils.xdg import xdg_opensnitch_dir, xdg_current_session
 import opensnitch.ui_pb2
 from opensnitch.ui_pb2_grpc import add_UIServicer_to_server
 from opensnitch import auth
@@ -66,6 +65,16 @@ def restrict_socket_perms(socket):
     except Exception as e:
         print("Unable to change unix socket permissions:", socket, e)
 
+def check_environ():
+    if xdg_current_session == "":
+        print("""
+
+  Warning: XDG_SESSION_TYPE is not set.
+    If there're no icons on the GUI, please, read the following comment:
+    https://github.com/evilsocket/opensnitch/discussions/999#discussioncomment-6579273
+
+""")
+
 def supported_qt_version(major, medium, minor):
     q = QtCore.QT_VERSION_STR.split(".")
     return int(q[0]) >= major and int(q[1]) >= medium and int(q[2]) >= minor
@@ -153,6 +162,7 @@ Examples:
         maxmsglen = cfg.getMaxMsgLength()
 
         service = UIService(app, on_exit, start_in_bg=args.background)
+        check_environ()
         localserver.newConnection.connect(service.OpenWindow)
         # @doc: https://grpc.github.io/grpc/python/grpc.html#server-object
         server = grpc.server(futures.ThreadPoolExecutor(),

ui/opensnitch/utils/xdg.py

@@ -105,5 +105,6 @@ _home = os.path.expanduser('~')
 xdg_config_home = os.environ.get('XDG_CONFIG_HOME') or os.path.join(_home, '.config')
 xdg_runtime_dir = get_runtime_dir(False)
 xdg_current_desktop = os.environ.get('XDG_CURRENT_DESKTOP')
+xdg_current_session = os.environ.get('XDG_SESSION_TYPE')
 
 xdg_opensnitch_dir = get_run_opensnitch_dir()