Master Linux Environment Variables: Multiple Configuration Methods & Loading Order

Linux Environment Variable Configuration

When installing software manually, you often need to set environment variables. The examples below assume Ubuntu 14.0, user uusama, and the MySQL binary directory /home/uusama/mysql/bin.

Reading Environment Variables

Use export to list all defined variables.

Use echo $PATH to display the current PATH value.

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

The PATH variable contains a colon‑separated list of directories that the shell searches for executable files.

Method 1: export PATH

Directly modify PATH with the export command:

export PATH=/home/uusama/mysql/bin:$PATH
# or place the new path at the end
export PATH=$PATH:/home/uusama/mysql/bin

Effective immediately.

Only affects the current terminal session.

Applies 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 after running source ~/.bashrc.

Permanent for the user.

Only the current user is affected.

If later files overwrite PATH, the change may not take effect.

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

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

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

Effective when a new login shell starts or after source ~/.bash_profile.

Permanent for the user.

If ~/.bash_profile does not exist, edit ~/.profile or create a new file.

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

Requires root privileges:

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

Effective for all users after opening a new terminal or running source /etc/bashrc.

Permanent.

Applies system‑wide.

Method 5: Edit /etc/profile (system‑wide)

Also requires root privileges:

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

Effective for all users after a new login or source /etc/profile.

Permanent.

Applies system‑wide.

Method 6: Edit /etc/environment (system‑wide)

Requires root privileges:

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

Effective after a new login or source /etc/environment.

Permanent.

Applies system‑wide.

How Linux Loads Environment Variables

Environment variables are loaded in a specific order, which determines which definitions take precedence.

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

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

The system first reads /etc/environment, then /etc/profile, which may source /etc/bash.bashrc and scripts in /etc/profile.d/. After that, the user’s ~/.profile is read, which in turn may source ~/.bashrc. The .bashrc file is read for each interactive shell.

Testing the Loading Order

To verify the order, add the following line as the first line of each file listed below, replacing the placeholder with the file’s absolute path: export UU_ORDER="$UU_ORDER:/path/to/file" Files to modify:

/etc/environment

/etc/profile

/etc/profile.d/test.sh (optional)

/etc/bashrc or /etc/bash.bashrc

~/.bash_profile or ~/.profile

~/.bashrc

After editing, open a new terminal and run echo $UU_ORDER. The output reveals the loading sequence, which is:

/etc/environment

/etc/profile

/etc/bash.bashrc

/etc/profile.d/test.sh

~/.profile

~/.bashrc

Additional Tips

Create a custom file (e.g., uusama.profile) with a series of export statements, then source it from ~/.profile to load project‑specific variables on login.

Define command aliases with alias, such as alias rm="rm -i", and place them in ~/.profile for convenient use.