How to set environment (PATH) variable permanently in Linux

There is a time when every Linux Administrator gets stuck at a point of his career when he/she has to set a custom path or any other environment variable permanently in the Linux machine.
Suppose you have added a new path to the PATH variable using the shell but you might observe that every time you switch terminal the PATH variable does not works.
 
Solution
To make this issue to be resolved permanently you need to add the variable inside .bashrc or .bash_profile file inside the home folder of the user.
For example, you want to add a PATH variable for root user so you need to add the path inside ~/.bashrc or ~/.bash_profile
Now the confusion comes which file should we place the variable or inside both the files?
 

Difference between .bashrc and .bash_profile

Every time you login to a Linux (Red Hat) machine .bash_profile file is executed

but
In case you are already logged in and you open a new terminal then .bashrc file is executed
So, basically you can put the environment variable inside any of the two files. As per me I would advice you to put the same inside .bash_profile.

WHY?

Have a look at .bash_profile file

# less ~/.bash_profile
# Get the aliases and functions
if [ -f ~/.bashrc ]; then
        . ~/.bashrc
fi
# User specific environment and startup programs
PATH=$PATH:$HOME/bin
export PATH
export PATH=$PATH:/usr/local/samba/bin