I upgraded one of our Red Hat Enterprise Linux VMs to Tomcat 7.0.4 tonight, did a bit of Apache reconfiguration, and when I restarted Apache I got a "document root doesn't exist" error even though in fact the document root does exist. (Trust me Apache, it's there.)
I double-checked the owners and permissions of all the directories in question and everything was identical to how things are set on another RHEL VM in this cluster on which I haven't upgraded Tomcat and done the reconfiguration yet. I was at a bit of a loss, so I googled around a bit and the prevailing sentiment seemed to be this was related to either A) a config file copied from a Windows box and the line breaks were throwing things off (wasn't applicable in my case), or B) the fact that SELinux was enabled.
If you've been around the Red Hat flavors of Linux long enough you'll remember that SELinux used to be absolutely horrible. For years the very first thing you had to do on Red Hat and Fedora to get anything working at all was turn SELinux off, and for a long time I believe it was even Red Hat's recommendation under their breath to just shut it off. It's gotten better over the years, and honestly stays out of the way to the point where I'd almost forgotten about it.
Since I didn't have anything else to try, however, I went into /etc/sysconfig/selinux and changed SELINUX=enforcing to SELINUX=disabled, restarted the server, and voila the complaining from Apache went away.
What I still don't get is A) why this isn't occurring on my other RHEL box with the same setup, and B) why it just started happening now. The only potential weirdness here is that my document root is a symlink, but again, it's been that way since I setup up these boxes originally and it hasn't been an issue.
So if you run into this same problem the fix (at least until I have more information about why it's happening) is to disable SELinux, but if anyone has more ideas about why this might be happening I'd love to hear them.