When needing to allow a less restrictive basedir setting in Plesk for a domain you could modify the sites vhost.conf file normally found or created in /var/www/vhosts/yourdomain.com/conf/ with something like:

<Directory /var/www/vhosts/yourdomain.com/httpdocs/>
php_admin_value open_basedir "/var/www/vhosts/yourdomain.com/httpdocs:/tmp:/php/includes"
</Directory>

Then run:

/usr/local/psa/admin/bin/websrvmng –reconfigure-vhost –vhost-name=yourdomain.com

Or to disable open_basedir you could put in:??

php_admin_value open_basedir none