How to Set Display Environment Variable in Linux: A Step-by-Step Guide

Success in Linux often hinges on mastering environment variables. Today, we’re focusing on a specific one: the DISPLAY variable. The DISPLAY variable plays a crucial role, letting your system know where to display an application’s graphical output. If you want your applications to open up on a specific screen or terminal, knowing how to set the DISPLAY environment variable is essential.

When we’re running applications, especially in a multi-user or remote environment, correctly configuring the DISPLAY variable ensures graphical tools appear where we need them. Here’s how you can set it effortlessly: in your shell, use export DISPLAY=:0.0 to set it for your current session. This command tells your system to display graphical output on the first display screen.

But what if you frequently switch displays or need the setting to persist? In such cases, adding the line export DISPLAY=:0.0 to your .bashrc or .profile file can be a lifesaver. This approach sets the environment variable for every session, saving you the hassle of repeatedly configuring it. Setting this correctly ensures our applications play nice with our chosen display, whether we’re working locally, remotely, or handling multiple users.

Understanding Environment Variables

Environment variables are crucial in managing how applications function within the Linux environment. They bridge user commands and system functions by storing configuration values accessible to multiple processes.

Definition and Purpose

Environment variables are key-value pairs used to configure the operating systems and applications. They serve to pass useful information such as user preferences or application settings. For instance, the DISPLAY variable tells graphical applications where to render their interface, which is critical to our intentions of setting it up.

Common environment variables include:

Variables like these aid in controlling software behavior and user settings.

Scope of Environment Variables

Scope determines the availability and longevity of environment variables. We can classify them as session-specific or system-wide.

Session-specific variables exist only within the terminal session you define them in. Once we log out, these variables vanish. Commands like export VAR=value help in temporarily setting these variables.

System-wide variables, on the other hand, persist across user sessions and reboots. We define these in files like /etc/environment or /etc/profile, ensuring all users and processes have access.

Choosing the right scope for your environment variables is essential. If you need temporary settings for quick tasks, session-specific is your guy. For lasting configurations, always aim for system-wide setups, which provide reliability and consistency.

Working With Environment Variables in Linux

In Linux, environment variables play a pivotal role in controlling the behavior of your system. They help manage the settings and preferences needed for various applications and system processes.

Listing and Displaying Variables

To see all the environment variables set in our current session, we can use the command printenv. This displays all the current settings. Using env, another handy command, lists all environment variables too.

printenv
env

For checking specific variables, we use echo followed by the variable name. For instance, to check the DISPLAY variable:

echo $DISPLAY

Adding grep helps filter the environment variables we are interested in. For example:

printenv | grep DISPLAY

Creating and Exporting New Variables

Creating a new environment variable is simple. First, we assign a value to a variable, like so:

MY_NEW_VAR='HelloWorld'

Then, we use the export command to make it an environment variable, ensuring it is available to all sub-processes.

export MY_NEW_VAR

Alternatively, we combine both steps:

export MY_NEW_VAR='HelloWorld'

In our .bashrc or .profile file, we can add these lines for persistence across sessions. Adding variables in these files ensures they are set every time we start a new terminal session.

Modifying and Unsetting Variables

Sometimes, we need to change the value of an existing environment variable. We simply assign a new value and export it:

export MY_EXISTING_VAR='NewValue'

To unset or remove an environment variable, we use the unset command:

unset MY_EXISTING_VAR

This removes the variable from the current session. For completeness, ensure to remove any corresponding lines from configuration files like .bashrc to avoid setting it in future sessions.

Environment Configuration Files

When setting environment variables in Linux, it’s crucial to understand where and how to configure them. Different files serve different purposes and knowing which to use can optimize your workflow and system management.

System-level Configuration

To set environment variables globally, we often use system-level files. /etc/environment is the go-to file for setting system-wide environment variables. This file is straightforward and doesn’t require shell scripting:

Another crucial file is /etc/profile. It’s sourced at login for all users, ensuring commands are executed and environment variables are set. Any variable defined here is available across user sessions, making it key for shared environments:

User Configuration in Bash

For user-specific configurations, ~/.bashrc and .bash_profile are indispensable. .bashrc is ideal for setting shell-specific variables and aliases. Since it’s read for interactive non-login shells, it’s perfect for everyday terminal commands. Add your desired environment variables like so:

export DISPLAY=paxbox1.paxco.com:0.0

.bash_profile is read during user login. It’s great for setting environment variables you need at session start. Place your settings here if they need to be available right from the login process:

export PATH=$PATH:$HOME/bin

To apply changes without logging out, use the source command. This ensures your session updates with the new variables immediately:

source ~/.bashrc

Also, remember the home directory holds these configuration files, making them user-specific and easily accessible for tweaks.

Advanced Environment Variable Concepts

Understanding advanced concepts related to environment variables can significantly enhance our ability to manage Linux environments. We’ll explore how environment variables behave in scripts and subshells and discuss some special variables that can be particularly useful.

Environment Variables in Scripts and Subshells

When we write shell scripts, environment variables play a crucial role in how commands interact with each other. One important point is that variables exported in a script are only available to child processes and not to the parent shell.

Here’s an example:

#!/bin/bash
export MY_VAR="Hello"
echo $MY_VAR # This will output "Hello"

However, if we create a subshell using parentheses, the variable defines within it remains local to that subshell:

(
  MY_VAR="Hello from subshell"
  echo $MY_VAR # This will output "Hello from subshell"
)
echo $MY_VAR # This will output nothing or the value from the parent shell

Remember, PATH variables in scripts determine where the shell looks for executable files, impacting script behavior.

Special Environment Variables

Certain environment variables have special meanings and uses. For example, $HOME holds the current user’s home directory path. This is handy for writing scripts that need to operate in the user’s space:

cd $HOME
echo $HOME # Outputs the home directory

$UID stores the user ID of the current user, allowing scripts to take actions based on user privileges:

if [ "$UID" -eq "0" ]; then
  echo "You are root"
else
  echo "You are a regular user"
fi

$SHLVL shows the shell level, helping us understand how deep we are in nested shells. This can be particularly useful for diagnosing script behaviors in multi-layered shell environments:

echo $SHLVL # Displays the current shell level

By grasping these special variables and their roles, we can write more reliable and dynamic scripts, efficiently interact with the host system, and better manage the locale and system paths.