databases are hosted on servers that are Linux-based (from Red Hat), with a software platform that includes Apache, PHP (with PEAR and Smarty), shards, Memcached, Squid, Perl, ImageMagick and Java; the system administration tools include Ganglia, SystemImager, Subcon and CVSup. Signed-in Flickr users can "Follow" the Photostreams of other Flickr photographers. Reciprocating this process is optional. A user's homepage contains a stream of their Contacts' photos at 2/3 screensize. Groups are another major means of interaction with fellow members of Flickr around common photography interests. A Flickr Group can be started by any Flickr user, who becomes its administrator and can appoint moderators. Groups may either be open access or invitation-only, and most have an associated pool of photos. The administrator of the Flickr group can monitor and set restrictions for the group, assign awards to members, and may curate and organize the photo content. Recent uploads to a group will sometimes appear on its members' homepages. Group photo pools may be displayed in the "Justified View" or as a slideshow. "Galleries" of photos from other photostreams may be curated by any signed-up Flickr user, provided the feature is not disabled by the photo's uploader, these are then publicly viewable. Any Flickr user can post comments to a Flickr photo on its photopage, unless this has been disabled by the uploader, and users can "favorite" a photo. A user's favorites can be viewed in a justified or slideshow display. Users of Windows Photo Gallery, Apple's iPhoto (version 8), Adobe's Lightroom 3.2, Apple's Aperture (version 3.0), darktable, and digiKam have the ability to upload their photos directly to Flickr. They can also automatically update their status on other social networking services when they upload their images to Flickr. Flickr provides a desktop client for Mac OS X and Windows that allows users to upload photos without using the web interface. Uploadr allows drag-and-drop batch uploading of photos, the setting of tags and descriptions for each batch, and the editing of privacy settings. Flickr has entered into partnerships with many third parties. Flickr had a partnership with the Picnik online photo-editing application that included a reduced-feature version of Picnik built into Flickr as a default photo editor. On April 5, 2012, Flickr replaced Picnik with Aviary as its default photo editor. In addition to using commercial mapping data, Flickr now uses OpenStreetMap mapping for various cities; this began with Beijing during the