var folder is one thing, to really check though you'll need to check the rights on the actual view cache files, located in var/<site_name>/cache/content/<siteaccess>/*.cache
To rule out a couple of pit falls you could try to clear the cache from the front end, typing in the /setup/cache url manually while logged in as admin.
<i>var/<site_name>/cache/content/<siteaccess>/*.cache</i> I checked this file and www-data has rw access, so it should be ok.
<i>To rule out a couple of pit falls you could try to clear the cache from the front end, typing in the /setup/cache url manually while logged in as admin.</i>
I tried it and it works ! Why is this working on the front-end but not in back-end ?
well there could be many different thing, is viewcache disabled in admin part?(but you would have noticed that, since the view cache check box would have been disabled in setup/cache) do they share the [FileSettings]VarDir setting? and are you sure there isn't anything wrong with the RelatedSiteAccessList setting?
Post your override/site.ini.append.php file (but without the sensitive parts like db settings and site name/url/domain).
> I have a folder for each siteaccess in the var folder (var/fre, var/ger, var/eng and var/wess_admin).
This is the reason then, related siteaccess need to share var folder to be able to expire view cache and some other caches. But you can't just merge the var folders though, because you'll have to fix the path of images / files that has been uploaded in the fre/eng/ger siteaccesses(if you merge them with the wess_admin var folder).
Simple: When your doing something that triggers cache clear when you are in your admin siteaccess it will clear it's cache in the var/<site_name>/cache/* folders, where site name is taken from the ini settings you are currently using (settings for this siteaccess). Additionally it will try to clear cache for the related siteaccess on cache types that stores it's cache pr siteaccess(the sub folders).
