How To Quickly Fix Common JRun / ColdFusion Startup Problems
If you've ever poked around with the various JRun XML configuration files in ColdFusion before, chances are you've ran across a time where you've not been able to get JRun to start properly. This is not an end all, be all guide to fixing these problems, but I thought I'd pass a couple of tips that I use to troubleshoot these problems quickly. I've found that it's usually due to a wonky text editor breaking the XML somehow by virtue of character encoding or something of that sort, but here are some tips to quickly fix a JRun server that won't start.
Before making changes to jrun.xml or default-web.xml, make backups.
Admittedly I'm so used to working in these files that I sometimes don't do this. However, I always have a WAR file around of ColdFusion which I can extract the original default files from very quickly.
When I try to start JRun/ColdFusion, it will not start
Most likely jrun.xml has somehow been corrupted or has an incorrect entry. The quickest way to get going again is to restore this file from a backup and try editing it again. Obviously you can also do a diff between the backup and your current file as well and fix as necessary.
After JRun/ColdFusion starts, I get a "500 There is no web application configured to service your request" error
In this case, there is a high likelyhood that defaut-web.xml has somehow been corrupted. Again, restore this file from backup and/or compare the current version to your backup file and fix as necessary. Keep in mind sometimes a text editor can muck the file all up even though it looks exactly the same, so you'll want to try a different editor in that case.
Granted there are many more cases which can cause problems with JRun/ColdFusion, but these are the most common ones I come across. If neither of these help, it's time to start digging in the server logs as well as find-out what has changed with the server recently.