Those of us who have the wonderful job of managing a SharePoint farm know, installing patches can be a bit like playing roulette. This is especially true when installing Cumulative Updates, but not limited to.
Those of us who manage a SharePoint farm with multiple servers have definitely seen our fair share of messages like the one below.
Obviously, the first thing you need to verify, is that the noted patch is actually on all the servers. If it is, often we are then directed by sites, even mine, to manually run some combination of the PSCONFIG.exe command manually via powershell. This typically works because we’re forcing SharePoint to skip important version checks etc.
I highly recommend before you jump to any powershell that you follow the instructions on the site below.
What this site is doing is clearing your configuration cache on each server before you attempt to run the SharePoint Configuration Wizard on any of your servers. The instructions specifically indicate they are for SharePoint 2010, but they work for SharePoint 2013 as well.
I’ve found I’ve even had issues running the PSCONFIG.exe manually and I still cannot get the config to finish. Clearing the cache is what works. You may need to reboot your servers, and you may even need to clear the cache twice, but soon, it will likely resolve the issue. So if you’re sitting stuck at 10% for forever, kill that PSCONFIG.exe task in the Task Manager and clear your cache. But don’t thank me, thank James Waymire, the author of the above article.