Usually the client installation of opsi software packets is started when booting the client. At startup the user has to wait for the installation to finish, before the logon is granted. So it might be useful to do most of the software installation when the client is going to shut down.
The opsi module for installation on shutdown is providing that feature. It can be activated for clients by a productswitch of the opsi-client-agent. The installation on shutdown module is based on the Windows shutdown script mechanism per Local GroupPolicy. Shutdown scripts allow to run tasks at shutdownwhen the user is logged off already, but all the system services are still available.
Per shutdown script an opsi task is executed, which triggers the opsiclientd installation process and waits for the installation to be completed. Then the system shutdown is continued. The new precondition 'installation_pending' manages, that ongoing installations are finished before the user logs on.
At the moment, the simultaneous use of both "WAN extension" and "installation on shutdown extension" is not supportet. On the same opsi server with different clients, these opsi extensions can be used.
Since May 2015 "installation on shutdown" is part of the free opsi core.