How do you find the environment for a running process?

Linux

cat /proc/<pid>/environ

Even though /proc/<pid>/environ has a size of 0, running a cat will still return the environment for this process. This file is just a kind of link to the actual location where the enviroment for this process is stored.

The ouput of the command above is not very readable since all strings are separated by NUL and not newlines. To convert them to newlines, you can use:

strings -f /proc/<pid>/environ

or

(cat /proc/<PID>/environ; echo) | tr "00" "n"

or

tr '' 'n' < /proc/<pid>/environ

or

xargs --null --max-args=1 echo < /proc/<pid>/environ

or

cat /proc/<pid>/environ | perl -pne '$a=chr(0);s/$a/n/g'

Note: you can get the pids of a process by using
$ pidof httpd

This return a space separated list of the PIDs of all httpd processes.

Mac OS X

ps -p <pid> -wwwE

AIX

ps eww <pid>

Solaris

pargs -e <pid>

HP-UX

The only way is to attach gdb to the process and examine _environ.

Windows