I have a linux instance that I set up some time ago.  When I fire it up and log in as root there are some environment variables that I set up but I can't remember or find where they came from.  I've checked ~/.bash_profile, /etc/.bash_rc, and all the startup scripts.  I've run find and grep to no avail. I feel like I must be forgetting to look in some place obvious.  Is there a trick for figuring this out?
How to determine where an environment variable came from
bash;shell;environment variables
If you use the env command to display the variables, they should show up roughly in the order in which they were created.  You can use this as a guide to if they were set by the system very early in the boot, or by a later .profile or other configuration file.  In my experience, the set and export commands will sort their variables by alphabetical order, so that listing isn't as useful.