+ app: unix, windows: require root user on first launch

os_unix.go

@@ -3,6 +3,7 @@
 package main
 
 import (
+	"os"
 	"syscall"
 
 	"github.com/AdguardTeam/golibs/log"
@@ -19,3 +20,8 @@ func setRlimit(val uint) {
 		log.Error("Setrlimit() failed: %v", err)
 	}
 }
+
+// Check if the current user has root (administrator) rights
+func haveAdminRights() (bool, error) {
+	return os.Getuid() == 0, nil
+}