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The LOCKSS Daemon is the Java application that runs continuously on a preservation node server to collect digital objects into Archival Units, caches them on the server, computes a checksum to monitor the integrity of the data in the AU, and compares the checksum with the ocpies preserved on other nodes throughout the network. ("Daemon" is a common term for a computer program that runs continually as a background process to serve requests or perform scheduled tasks.)

From LOCKSS Technical Manual

LOCKSS caches: The LOCKSS caches are the nodes in the network in which digital objects will be preserved and monitored as archival units. One archival unit is typically a one-year collection (size: 1GB to 20GB). [...] The daemon is a java application which collects digital objects through http requests from the original website, store them inside the cache as an Archival Unit, computes an SHA-1 checksum and regularly monitors their integrity by comparing the preserved content with the other caches in the network with a specific voting protocol (LCAP). The AUs are collected at various moments in time by the different nodes in the network to reduce the risk of communication issues. The content is regularly recrawled from the original website if it is still available. If a new version of the AU is available, the previous version is kept but only the most recent AUs will be checked for fixity. A LOCKSS cache can also be configured as a proxy to deliver the preserved content. The LOCKSS cache local configuration can be managed through a web-based user interface. This interface allows local administrators to add or remove AUs from the cache, to view the daemon status and to modify the local cache configuration.
—From LOCKSS Technical Manual: Basic Private LOCKSS Network infrastructure (Plnwiki)