User Jobs

Users specify in the JDL the tag corresponding to the software release they need. This will ensure that only those sites run their jobs where the software is either installed and certified, or the software is on the site's SE and has been certified to install and run correctly on the site WNs. The users job needs a script to be run at the beginning that tests the value of the environmental variable VO_$<$EXP$>$_SW_DIR. In case this is "." a script provided by the experiment retrieves the version wanted from the SE and installs it locally. There are several ways the script can be told what the wanted release is. It is up to the experiments to define conventions to steer this. The experiment's install script should test that in case of local installation the provided scratch space is sufficient for installing the software and running the job. At the end of the job the software is removed by the batch system.
In case there is a path different than "." defined by the environmental variable the script does nothing but starts the user's program assuming the version in the path.
For the sites that are using the non-shared-file-system approach the performance might suffer. If a cache management system for local software is in place the changes to the experiments scripts should be small.