Where to Declare Environment Variables?

In the world of software development and system administration, environment variables serve as a key component in managing the behavior of various processes within an operating system. This article will guide you through the process of declaring environment variables in Ubuntu, focusing on both global and user-specific environment variables.

What are Environment Variables?

Environment variables are dynamic, named values that can affect the way running processes behave on a computer. They exist in every operating system, and are used to make the system aware of certain conditions or settings. They can be created, edited, saved, and deleted, and they can be accessed by software programs and the operating system itself.

Declaring Global Environment Variables

Global environment variables are those that are available system-wide and affect all users and processes. In Ubuntu, you have a couple of options for setting these.

/etc/environment

The recommended location for declaring global environment variables is the /etc/environment file. This file is not a script file, but rather a system file that holds global environment variable settings. It uses assignment expressions, with one per line. For example:

PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games"
JAVA_HOME="/usr/lib/jvm/java-8-oracle"

In this example, PATH and JAVA_HOME are environment variables, and the text within the quotes are the values assigned to these variables.

/etc/profile and /etc/bash.bashrc

While you can use /etc/profile or /etc/bash.bashrc for global environment variables, their functionality is limited in Ubuntu, and it’s generally recommended to avoid using these files for this purpose.

Declaring User-Specific Environment Variables

User-specific environment variables only affect the respective user’s environment. The process for setting these is slightly different than for global variables.

~/.pam_environment

The recommended location for user-specific environment variables is the ~/.pam_environment file. This file is loaded by the PAM system when a user session is started. It uses the same syntax as /etc/environment.

~/.profile

If ~/.pam_environment doesn’t work for you, you can use ~/.profile. This file is applied to most shells and may also be applied to your GUI session by the display manager, although this can vary depending on the display manager or display server being used.

~/.bash_profile or ~/.bash_login

For bash-specific shells, you can use ~/.bash_profile or ~/.bash_login. If either of these files exists, bash executes it instead of ~/.profile when bash is started as a login shell. Bash prefers ~/.bash_profile over ~/.bash_login. These files won’t influence a graphical session by default.

~/.bashrc

Another option for bash is ~/.bashrc, which may be the easiest place to set variables.

Conclusion

Understanding where and how to declare environment variables is crucial for managing your Ubuntu system effectively. Whether you’re setting global variables that affect all users or user-specific variables, you have several options to choose from. Remember to choose the method that best suits your needs and the specific behavior you want to achieve.

Remember, /etc/environment sets the default environment for all processes, while the user-specific files mentioned above only affect the respective user’s environment. Always be careful when setting environment variables, as incorrect settings can cause system instability or other unexpected behavior.