solved joomla error install template: Failed to create directory

log into your server and just simple:
chown www-data:www-data joomla/
chown www-data:www-data joomla/tmp/

When you copy your joomla directory into your /var/www/
 the directory permissions and owners get the user(root) permissions.
With that command chown www-data:www-data you resolve the job!
That's simple!
You will not find that respons in joomla's forums!