Master Linux Environment Variables: 6 Proven Configuration Methods

Linux Environment Variable Configuration

When installing custom software you often need to set environment variables. The examples assume an Ubuntu 14.0 system, user uusama, and a MySQL binary directory at /home/uusama/mysql/bin.

Reading Environment Variables

export

– lists all currently defined environment variables. echo $PATH – prints the value of the PATH variable.

uusama@ubuntu:~$ export
declare -x HOME="/home/uusama"
declare -x LANG="en_US.UTF-8"
... (other variables) ...
declare -x PATH="/home/uusama/bin:/home/uusama/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"

uusama@ubuntu:~$ echo $PATH
/home/uusama/bin:/home/uusama/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

The PATH variable defines the search order for executable commands, separated by colons. It can be defined with or without surrounding quotes.

Method 1: Direct export PATH

Use the export command to modify PATH directly:

export PATH=/home/uusama/mysql/bin:$PATH   # prepend MySQL bin
# or
export PATH=$PATH:/home/uusama/mysql/bin   # append MySQL bin

Effective immediately.

Only lasts for the current terminal session.

Applies only to the current user.

Remember to include the original $PATH to avoid overwriting existing entries.

Method 2: Edit ~/.bashrc

Add the export line to the end of ~/.bashrc:

vim ~/.bashrc
# add at the end
export PATH=$PATH:/home/uusama/mysql/bin

Effective when a new terminal is opened, or immediately after running source ~/.bashrc.

Persists permanently for the user.

Only affects the current user.

If another file later overwrites PATH, the change may be lost.

Method 3: Edit ~/.bash_profile (or ~/.profile )

Similar to ~/.bashrc, add the export line to the end of the file:

vim ~/.bash_profile
# add at the end
export PATH=$PATH:/home/uusama/mysql/bin

Effective after opening a new login shell or running source ~/.bash_profile.

Permanent for the user.

If ~/.bash_profile does not exist, edit ~/.profile instead.

Method 4: Edit /etc/bashrc (system‑wide)

Requires root privileges. Make the file writable, then add the export line:

chmod -v u+w /etc/bashrc
vim /etc/bashrc
# add at the end
export PATH=$PATH:/home/uusama/mysql/bin

Effective in new terminals or after source /etc/bashrc.

Permanent.

Applies to all users.

Method 5: Edit /etc/profile

Also system‑wide and requires root. The steps mirror Method 4:

chmod -v u+w /etc/profile
vim /etc/profile
# add at the end
export PATH=$PATH:/home/uusama/mysql/bin

Effective in new terminals or after source /etc/profile.

Permanent.

Applies to all users.

Method 6: Edit /etc/environment

This file is another system‑wide configuration point:

chmod -v u+w /etc/environment
vim /etc/environment
# add at the end
export PATH=$PATH:/home/uusama/mysql/bin

Effective in new terminals or after source /etc/environment.

Permanent.

Applies to all users.

How Linux Loads Environment Variables

Environment variables are defined either at the user level or the system level.

User‑level files: ~/.bashrc, ~/.profile (or ~/.bash_profile).

System‑level files: /etc/bashrc, /etc/profile, /etc/bash_profile, /etc/environment.

During a login, the shell reads ~/.bash_profile (or ~/.profile); if absent it reads ~/.bash_login, then ~/.bashrc.

Testing the Loading Order

Insert the same test variable UU_ORDER at the top of each file, appending the file name to its value. After opening a new terminal and running echo $UU_ORDER, the observed order is:

UU_ORDER:/etc/environment:/etc/profile:/etc/bash.bashrc:/etc/profile.d/test.sh:~/.profile:~/.bashrc

/etc/environment

/etc/profile

/etc/bash.bashrc

/etc/profile.d/test.sh

~/.profile

~/.bashrc

Detailed Loading Process

/etc/profile

loads /etc/bash.bashrc and then iterates over /etc/profile.d/*.sh. Afterwards, ~/.profile loads ~/.bashrc. The ~/.profile file is read only once at login, while ~/.bashrc is read for each interactive shell.

Additional Tips

Create a custom file such as uusama.profile, define variables with export, and source it from ~/.profile for project‑specific settings.

Define command aliases, e.g., alias rm="rm -i", and place them in ~/.profile for convenient, safer usage.