doc/operation: in Online backup, mention the necessary access rights of the backup...

It is a frequently asked question from users.

diff --git a/doc/operation.rst b/doc/operation.rst
index 9fa47c37b4440be3fc7dca722a5f4249de120c5b..ac04df4ff17915aa340d02f3e48b47a386317cad 100644 (file)
--- a/doc/operation.rst
+++ b/doc/operation.rst
@@ -956,7 +956,8 @@ their list::
 
     $ knotc zone-backup +backupdir /path/to/backup zone1.com. zone2.com. ...
 
-The backup directory should be empty or non-existing.
+The backup directory should be empty or non-existing and it must be accessible
+and writable for the :ref:`server_user` account under which knotd is running.
 The backup procedure will begin soon and will happen zone-by-zone
 (partially in parallel if more :ref:`server_background-workers` are configured).
 **The user shall check the logs for the outcome of each zone's backup attempt.**