Master Linux Environment Variables: 6 Proven Configuration Methods

Linux Environment Variable Basics

When installing custom software on Linux, configuring environment variables is often required. The examples assume Ubuntu 14.0, user uusama, and a MySQL binary directory at /home/uusama/mysql/bin.

Reading Environment Variables

Use export to list all currently defined environment 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"
... (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 directories the shell searches for executables, separated by colons. Quotes around the value are optional when using export.

Method 1: Direct export PATH

Modify PATH on the fly with:

export PATH=/home/uusama/mysql/bin:$PATH
# or prepend the new path
export PATH=$PATH:/home/uusama/mysql/bin

Effective immediately.

Only lasts for the current terminal session.

Applies to the current user.

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

Method 2: Edit ~/.bashrc

Add the following line at 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 be lost.

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

Similar to ~/.bashrc, add:

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 or create the file.

Method 4: Edit System File /etc/bashrc

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

# make writable if needed
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 system‑wide change.

Applies to every user.

Method 5: Edit System File /etc/profile

Also requires root. The steps mirror those for /etc/bashrc:

# make writable if needed
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 system‑wide change.

Applies to every user.

Method 6: Edit /etc/environment

This file sets system‑wide environment variables. After gaining write permission, add the export line:

# make writable if needed
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 for all users.

Applies system‑wide.

How Linux Loads Environment Variables

Linux reads configuration files in a specific order, and later definitions can overwrite earlier ones. The main categories are user‑level files ( ~/.bashrc, ~/.profile / ~/.bash_profile) and system‑level files ( /etc/bashrc, /etc/profile, /etc/environment).

Testing the Loading Order

To observe the order, add a line defining UU_ORDER in each file, appending the file’s name to the variable. Example for ~/.bash_profile: export UU_ORDER="$UU_ORDER:~/.bash_profile" After reopening a terminal, echo $UU_ORDER yields:

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

From this result, the loading sequence is:

/etc/environment

/etc/profile

/etc/bash.bashrc

/etc/profile.d/*.sh (e.g., test.sh)

~/.profile (or ~/.bash_profile)

~/.bashrc

Detailed File Loading

/etc/profile

loads /etc/bash.bashrc and then iterates over scripts in /etc/profile.d/. The user’s ~/.profile subsequently sources ~/.bashrc. The ~/.bashrc file is read each time a new interactive shell starts, while ~/.profile is read only at login.

# /etc/profile snippet
if [ "PS1" ]; then
  if [ "BASH" ] && [ "BASH" != "/bin/sh" ]; then
    if [ -f /etc/bash.bashrc ]; then
      . /etc/bash.bashrc
    fi
  else
    if [ "`id -u`" -eq 0 ]; then
      PS1='# '
    else
      PS1=' '
    fi
  fi
fi

if [ -d /etc/profile.d ]; then
  for i in /etc/profile.d/*.sh; do
    if [ -r i ]; then
      . i
    fi
  done
  unset i
fi

In ~/.profile:

# include .bashrc if it exists
if [ -n "${BASH_VERSION}" ]; then
  if [ -f "$HOME/.bashrc" ]; then
    . "$HOME/.bashrc"
  fi
fi
PATH="$HOME/bin:$HOME/.local/bin:$PATH"

Additional Tips

Create a custom profile file (e.g., uusama.profile) with many export statements, then source it from ~/.profile for project‑specific variables.

Define command aliases, such as alias rm="rm -i", by adding them to ~/.profile or ~/.bashrc for convenient usage.