EDG Make Gridmap (usually referred to by it's command-line name, mkgridmap), is a tool that creates a Globus grid-mapfile automatically. To create this file, it consults a list of VOMS servers and a configuration file that describes how to map the users in each virtual organization (VO) to local users. It was originally created by the European DataGrid (EDG) project, and is now maintained by the LHC Computing Grid (LCG) project.
In VDT 1.3.10 and earlier, edg-mkgridmap was invoked every 24 hours by a daemon called edg-gridmapfile-upgrade. In VDT 1.3.11, edg-mkgridmap is invoked every six hours by cron. In order to avoid having all VDT sites contact the VOMS servers simultaneously, we configure the cron job to pick a random time to run, then every six hours after that. For example, we might pick randomly 2:13am, then 8:13am, 2:13pm, and 8:13pm.