enviroment files -- How Is The Environment Established

Login shells read one or more startup files as shown below:

File	Contents
/etc/profile	A global configuration script that applies to all users.
~/.bash_profile	A user's personal startup file. Can be used to extend or override settings in the global configuration script.
~/.bash_login	If ~/.bash_profile is not found, bash attempts to read this script.
~/.profile	If neither ~/.bash_profile nor ~/.bash_login is found, bash attempts to read this file. This is the default in Debian-based distributions, such as Ubuntu.

Non-login shell sessions read the following startup files:

File	Contents
/etc/bash.bashrc	A global configuration script that applies to all users.
~/.bashrc	A user's personal startup file. Can be used to extend or override settings in the global configuration script.

In addition to reading the startup files above, non-login shells also inherit the environment from their parent process, usually a login shell.