Master Linux Environment Variables: Configuring, Reading, and Loading Order

Linux Environment Variable Configuration

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

Examples assume:

System: Ubuntu 14.0

Username: uusama

MySQL path: /home/uusama/mysql/bin

Linux Reading Environment Variables

Methods to read:

export command shows all defined variables

echo $PATH prints the current PATH value

Example output:

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 colons; quotes are optional.

Method 1: export PATH

Directly modify PATH with export:

export PATH=/home/uusama/mysql/bin:$PATH
# or put PATH first
export PATH=$PATH:/home/uusama/mysql/bin

Notes:

Effective immediately

Only for the current terminal session

Applies to the current user only

Remember to include the existing $PATH to avoid overwriting

Method 2: vim ~/.bashrc

Edit ~/.bashrc and add at the end:

vim ~/.bashrc

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

Notes:

Effective when opening a new terminal or after running source ~/.bashrc Permanent

Applies to the current user only

May be overridden by later files

Method 3: vim ~/.bash_profile

Similar to ~/.bashrc, edit ~/.bash_profile (or ~/.profile) and add:

vim ~/.bash_profile

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

Notes:

Effective on new terminal or after source ~/.bash_profile Permanent

Current user only

If the file is missing, edit ~/.profile or create one

Method 4: vim /etc/bashrc

System-wide configuration requires root:

# make /etc/bashrc writable
chmod -v u+w /etc/bashrc
vim /etc/bashrc

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

Notes:

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

Applies to all users

Method 5: vim /etc/profile

Similar to /etc/bashrc:

# make /etc/profile writable
chmod -v u+w /etc/profile
vim /etc/profile

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

Notes:

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

All users

Method 6: vim /etc/environment

System environment file:

# make /etc/environment writable
chmod -v u+w /etc/environment
vim /etc/environment

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

Notes:

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

All users

How Linux Loads Environment Variables

Variables are loaded in a specific order; later definitions can override earlier ones.

Classification of Environment Variable Files

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

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

Login shells read ~/.bash_profile (or ~/.profile) first, then ~/.bashrc; non‑login shells read ~/.bashrc directly.

Testing Load Order

Define a variable UU_ORDER in each file, appending the file name, then inspect its value. export UU_ORDER="$UU_ORDER:~/.bash_profile" After opening a new terminal, echo $UU_ORDER shows the order:

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

Observed load order:

/etc/environment

/etc/profile

/etc/bash.bashrc

/etc/profile.d/test.sh

~/.profile

~/.bashrc

Detailed File Loading

/etc/profile loads /etc/bash.bashrc and scripts in /etc/profile.d/*.sh:

# /etc/profile: system-wide .profile file for the Bourne shell
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

~/.profile includes ~/.bashrc if it exists:

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

.profile is read once at login; .bashrc is read for each shell invocation.

Tips

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

Define command aliases, such as alias rm="rm -i", and add them to ~/.profile for convenient safe deletions.