While writing grains and pillars, you may encounter some difficulties. Let's take a look at the most common problems you might have.
You may find that when you issue a grains.items command from the Master, your dynamic grains aren't showing up. This can be difficult to track down, because grains are evaluated on the Minion, and any errors aren't likely to make it back over the wire to you.
When you find that dynamic grains aren't showing up as you expect, it's usually easiest to log in to the Minion directly to troubleshoot. Open up a shell and try issuing a salt-call command to see if any errors manifest themselves. If they don't immediately, try adding --log-level=debug to your command to see if any errors have been hiding at that level. Using a trace log level might also be necessary.