feat: Inherits uid/gid from the PLC program when not executed as root

If the daemon is not executed as root, no alternative UID/GID can be set
for the control program. In this case, the IDs of the daemon process
are inherited to the control program.

src/revpipyload/plcsystem.py

@@ -91,6 +91,8 @@ class RevPiPlc(Thread):
         """Setzt UID und GID fuer das PLC Programm."""
         proginit.logger.debug("enter RevPiPlc._setuppopen()")
 
+        # If we are not root, the process is same uid / gid as daemon
+        if os.getuid() == 0:
             proginit.logger.info("set uid {0} and gid {1} for plc program".format(self.uid, self.gid))
 
             # Set user last to hold root right to do the group things
@@ -101,6 +103,12 @@ class RevPiPlc(Thread):
                 proginit.logger.warning("could not initialize the group access list with all groups")
             os.setgid(self.gid)
             os.setuid(self.uid)
+        else:
+            proginit.logger.info(
+                "leave uid {0} and gid {1} for plc program, because not executed as root".format(
+                    os.getuid(), os.getgid()
+                )
+            )
 
         proginit.logger.debug("leave RevPiPlc._setuppopen()")