How to show environment variable for a process id (pid)

Sometimes it may be useful to see what environment variables were passed to a process. e.g. you may want to see LC_ALL value for a long running or command or environment variable passed to a cron process. Here are the steps to find env variables passed to a process given its pid on Ubuntu Linux. This approach should work on other Linux systems also.

Each process keeps the list of environment variables in file /proc/[pid]/environ. Here are quick steps to find environment variables for running apache2 daemon.

1. First find the pid of running apache2 process.

   $ ps aux | grep apache2 | grep root
   root     27220  0.0  3.1 432004 31892 ?        Ss   Oct04   0:39 /usr/sbin/apache2 -k start
   

2. Now run the following to display environment variable for above process id:

   $ sudo cat /proc/11824/environ | tr '\0' '\n'
   APACHE_RUN_DIR=/var/run/apache2
   APACHE_PID_FILE=/var/run/apache2/apache2.pid
   PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
   APACHE_LOCK_DIR=/var/lock/apache2
   LANG=C
   APACHE_RUN_USER=www-data
   APACHE_RUN_GROUP=www-data
   APACHE_LOG_DIR=/var/log/apache2
   PWD=/
   

   You can also use Linux cli utility strings to print content of /proc/[pid]/environ in human readable format as shown below:

   $ sudo strings /proc/11824/environ