An example of a "vhost.conf" with Plesk

As Plesk overwrites the php.ini for the Apache webserver, you have to create a file vhost.conf inside the webuser's directory in the folder conf with the following content:

DocumentRoot /var/www/vhosts/meinedomain.com/httpdocs/web
<Directory /var/www/vhosts/meinedomain.com/httpdocs/web>
  <IfModule mod_php5.c>
    php_value memory_limit 512M
    php_admin_value open_basedir "/var/www/vhosts/meinedomain.com/httpdocs:/tmp:/usr/bin:/usr/local/bin"
    php_admin_value post_max_size 1024M
    php_admin_value upload_max_filesize 1024M
    php_admin_value safe_mode Off
    php_admin_value register_argc_argv On
    php_admin_value register_globals Off
  </IfModule>
  <IfModule sapi_apache2.c>  
    php_value memory_limit 512M
    php_admin_value open_basedir "/var/www/vhosts/meinedomain.com/httpdocs:/tmp:/usr/bin:/usr/local/bin"
    php_admin_value post_max_size 1024M
    php_admin_value upload_max_filesize 1024M
    php_admin_value safe_mode Off
    php_admin_value register_argc_argv On
    php_admin_value register_globals Off
  </IfModule>
</Directory>

Next Plesk has to be informed to import the modifications. This can be done with the following command:

/usr/local/psa/admin/sbin/websrvmng --reconfigure-vhost --vhost-name=MEINEDOMAIN.TLD

On Ubuntu:

/opt/psa/admin/bin/websrvmng --reconfigure-vhost --vhost-name=MEINEDOMAIN.TLD 

The vhost.conf configuration only works for the Apache Webserver. For the php-cli the values have to be entered into the according php.ini additionally.