So more trouble with the OMV box and associated link to the Synology Diskstation! Another story.
However I have moved the Family History site based on Webtrees to the OMV having mistakenly deleted every file in the /volume1/web directory. Luckly it changes very seldomly and I had an sql backup which was OK.
However the install does not seem to give the right directory or file permissions. I have done a CHOWN to give www-data as both user and group but now want to recursively have directories as 755 an files as 644.
find /media/www/webtrees -type d -exec chmod 755 {} \;
and
find /media/www/webtrees -type f -exec chmod 644 {} \;
does the trick.