How to determine where an environment variable came from

Question

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?

Answer 1

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.

Answer 2

If you put set -x in your .profile or .bash_profile, all subsequent shell commands will be logged to standard error and you can see if one of them sets these variables. You can put set -x at the top of /etc/profile to trace it as well. The output can be very verbose, so you might want to redirect it to a file with something like exec 2>/tmp/profile.log.

If your system uses PAM, look for pam_env load requests in /etc/pam.conf or /etc/pam.d/*. This module loads environment variables from the specified files, or from a system default if no file is specified (/etc/environment and /etc/security/pam_env.conf on Debian and Ubuntu). Another file with environment variable definitions on Linux is /etc/login.defs (look for lines beginning with ENV_).

Answer 3

Check your startup scripts for files that they source using . (dot) or source. Those files could be in other directories besides /etc and $HOME.

Answer 4

@Cian is correct. Other than using find and grep, there isn't much you can do to discover where it came from. Knowing that it is indeed an environment variable, I would attempt focusing your search in /etc/ and your home directory. Replace VARIABLE with the appropriate variable you're searching for:

$ grep -r VARIABLE /etc/*

$ grep -r VARIABLE ~/.*

Answer 5

Other than find and grep (which seem to have already failed), I'm afraid not.