diff --git a/check_clientbackup b/check_clientbackup
index 924c384c66033b94e098e59ac1ac165913987fce..7bb8c745682ff6d58f994d6465d76387705323c2 100755
--- a/check_clientbackup
+++ b/check_clientbackup
@@ -43,6 +43,10 @@ Licence: GNU GPL 3
 ______________________________________________________________________
 
 Show status of IML backup.
+See https://os-docs.iml.unibe.ch/iml-backup/
+
+It returns with state UNKNOWN if no backup has been performed yet.
+It switches to ERROR an error occured during backup process.
 
 SYNTAX:
 $_self [-d DIRECTORY]