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+# Online Update
+
+Online update implementation based on Mozilla's MAR format + update mechanism
+
+Parts of this code are copied from the mozilla repository, and adapted to
+LibreOffice needs:
+
+`firefox/modules/libmar` -> `onlineupdate/source/libmar`
+`firefox/toolkit/mozapps/update` -> `onlineupdate/source/update`
+
+The source/service directory contains the code for the silent windows updater that avoids the
+repeated administrator check for an update.
+
+## Note
+
+The updater executable should not depend on any other dynamic library in the LibreOffice
+installation as we would need to copy that one also to a temporary directory during update. We can't
+update any library or executable that is currently in use. For the updater executable we solve this
+problem by copying the updater before using it to a temporary directory.
+
+On Windows we use the system to provide us with a crypto library whereas on Linux we use NSS.
+
+## Update Procedure
+
+The updater executable is run two times. In a first run, the current installation is copied to an
+`update` directory and the update is applied in this `update` directory. During the next run, a
+replacement request is executed. The replacement request removes the old installation directory and
+replaces it with the content of the `update` directory.
+
+### User Profile in the Installation Directory
+
+The archive based installations have the user profile by default inside of the installation
+directory. During the update process this causes some problems that need special handling in the
+updater.
+
+* The `update` directory is inside of the user profile resulting in recursive copying.
+* During the replacement request the updater log is in the user profile, which changes location from
+the actual location to a backup location.