diff --git a/doc/erko_howto_tools.txt b/doc/erko_howto_tools.txt
index f1eff095dee90cfb466a4ac0b68bd37a8aef4cbd..3371412936503e7732066da2f29826cee4651c27 100755
--- a/doc/erko_howto_tools.txt
+++ b/doc/erko_howto_tools.txt
@@ -801,6 +801,9 @@ sudo chgrp -R software dirname  # recursively change group of 'dirname' to 'soft
 
 sudo chown user_name file_name  # change user,group
 
+# Linux upgrade
+https://linuxmint-user-guide.readthedocs.io/en/latest/upgrade-to-mint-20.html
+
 *******************************************************************************
 * ICT diensten
 *******************************************************************************