Changes to environment variables survive as long as the shell runs. When you exit the shell (or logout) these settings are lost. If you want to customize the environment and have those changes take effect every time you login, you need to record those settings in your startup scripts. If you are using bash, that means you want to edit the .bashrc file in your home directory. Simply add the relevant variable assignments (and the export commands) to this file. Since .bashrc is read every time you login to the computer, your customizations will become permanent.