Master Linux Environment Variables: Configure, Read, and Understand Loading Order

Linux Environment Variable Configuration

When installing software you often need to set environment variables; below are various methods.

System: Ubuntu 14.0

Username: uusama

Need to configure MySQL environment variable path: /home/uusama/mysql/bin

Reading Linux Environment Variables

Methods: export shows all defined environment variables. echo $PATH prints 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 LESSCLOSE="/usr/bin/lesspipe %s %s"
declare -x LESSOPEN="| /usr/bin/lesspipe %s"
declare -x LOGNAME="uusama"
declare -x MAIL="/var/mail/uusama"
declare -x PATH="/home/uusama/bin:/home/uusama/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
declare -x SSH_TTY="/dev/pts/0"
declare -x TERM="xterm"
declare -x USER="uusama"

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 command search paths separated by ':' and can be modified with export.

Method 1: export PATH

Directly modify PATH:

export PATH=/home/uusama/mysql/bin:$PATH
# or put PATH at the end
export PATH=$PATH:/home/uusama/mysql/bin

Effective immediately.

Only for the current terminal session.

Applies to the current user.

Remember to include the original $PATH to avoid overwriting.

Method 2: vim ~/.bashrc

Edit ~/.bashrc and add at the end:

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

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

Permanent for the user.

Method 3: vim ~/.bash_profile

Similar to ~/.bashrc, edit and add the same line.

vim ~/.bash_profile
export PATH=$PATH:/home/uusama/mysql/bin

Effective after new login or source ~/.bash_profile.

Permanent for the user.

Method 4: vim /etc/bashrc

System‑wide configuration requires root:

# make file writable if needed
chmod -v u+w /etc/bashrc
vim /etc/bashrc
# add at the last line
export PATH=$PATH:/home/uusama/mysql/bin

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

Method 5: vim /etc/profile

System‑wide configuration similar to /etc/bashrc:

chmod -v u+w /etc/profile
vim /etc/profile
export PATH=$PATH:/home/uusama/mysql/bin

Effective after new terminal or source /etc/profile.

Method 6: vim /etc/environment

Another system‑wide file requiring root:

chmod -v u+w /etc/environment
vim /etc/environment
export PATH=$PATH:/home/uusama/mysql/bin

Effective after new terminal or source /etc/environment.

Linux Environment Variable Loading Principles

Environment variables are loaded in a specific order, affecting which definition takes effect.

Classification

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

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

When a login shell starts, Bash reads ~/.bash_profile (or ~/.profile), then ~/.bashrc. System files are read earlier: /etc/environment → /etc/profile → /etc/bash.bashrc → files in /etc/profile.d → user files.

Testing Loading Order

By adding export UU_ORDER="$UU_ORDER:/path/to/file" at the top of each file and echoing $UU_ORDER, the observed order is:

/etc/environment

/etc/profile

/etc/bash.bashrc

/etc/profile.d/test.sh

~/.profile

~/.bashrc

File Loading Details

/etc/profile loads /etc/bash.bashrc and scripts in /etc/profile.d/*.sh. ~/.profile loads ~/.bashrc. ~/.bashrc is read for each non‑login shell.

Tips

Create a project‑specific file (e.g., uusama.profile) and source it from ~/.profile to load custom variables on login.

Define command aliases with alias in ~/.profile for convenient usage.