How to permanently set environmental variables on Linux

You can add it to the file .profile or your login shell profile file (located in your home directory).

To change the environmental variable "permanently" you'll need to consider at least these situations:

1. Login/Non-login shell
2. Interactive/Non-interactive shell

bash

1. Bash as login shell will load /etc/profile, ~/.bash_profile, ~/.bash_login, ~/.profile in the order
2. Bash as non-login interactive shell will load ~/.bashrc
3. Bash as non-login non-interactive shell will load the configuration specified in environment variable $BASH_ENV

$EDITOR ~/.profile
#add lines at the bottom of the file:  
     export LD_LIBRARY_PATH=/usr/lib/oracle/11.2/client64/lib
     export ORACLE_HOME=/usr/lib/oracle/11.2/client64

zsh

$EDITOR ~/.zprofile
#add lines at the bottom of the file:  
     export LD_LIBRARY_PATH=/usr/lib/oracle/11.2/client64/lib
     export ORACLE_HOME=/usr/lib/oracle/11.2/client64

ksh

$EDITOR ~/.profile
#add lines at the bottom of the file:  
     export LD_LIBRARY_PATH=/usr/lib/oracle/11.2/client64/lib
     export ORACLE_HOME=/usr/lib/oracle/11.2/client64

bourne

$EDITOR ~/.profile
#add lines at the bottom of the file:  
     LD_LIBRARY_PATH=/usr/lib/oracle/11.2/client64/lib     
     ORACLE_HOME=/usr/lib/oracle/11.2/client64
     export LD_LIBRARY_PATH ORACLE_HOME

csh or tcsh

$EDITOR ~/.login
#add lines at the bottom of the file:  
     setenv LD_LIBRARY_PATH /usr/lib/oracle/11.2/client64/lib
     setenv ORACLE_HOME /usr/lib/oracle/11.2/client64

If you want to make it permanent for all users, you can edit the corresponding files under /etc/, i.e. /etc/profile for Bourne-like shells, /etc/csh.login for (t)csh, and /etc/zsh/zprofile and /etc/zsh/zshrc for zsh.

Another option is to use /etc/environment, which on Linux systems is read by the PAM module pam_env and supports only simple assignments, not shell-style expansions. (See Debian's guide on this.)

These files are likely to already contain some assignments, so follow the syntax you see already present in your file.

Make sure to restart the shell and relogin the user, to apply the changes.

If you need to add system wide environment variable, there's now /etc/profile.d folder that contains sh script to initialize variable.
You could place your sh script with all you exported variables here.
Be carefull though this should not be use as a standard way of adding variable to env on Debian.

Reference