Master Linux Environment Variables: 6 Methods & Loading Order Explained

Linux Environment Variable Configuration

When installing custom software, configuring environment variables is often required; the following methods illustrate various ways to set them.

Example environment:

System: Ubuntu 14.0

Username: uusama

MySQL binary path to add: /home/uusama/mysql/bin

Reading Environment Variables in Linux

Common commands: export – displays all defined environment variables. echo $PATH – outputs 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 the directories searched for executable commands, separated by colons. Quotes are optional when using export.

Method 1: export PATH

Directly modify PATH with the export command:

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 original $PATH to avoid overwriting existing entries.

Method 2: Edit ~/.bashrc

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

vim ~/.bashrc
# Append 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 affects the current user.

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

Method 3: Edit ~/.bash_profile

Similar to ~/.bashrc, add the export line to ~/.bash_profile (or ~/.profile on some systems):

vim ~/.bash_profile
# Append 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.

Only affects the current user.

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

Method 4: Edit /etc/bashrc

System‑wide configuration requires root privileges:

# Make the file writable if needed
chmod -v u+w /etc/bashrc
vim /etc/bashrc
# Append at the end
export PATH=$PATH:/home/uusama/mysql/bin

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

Permanent.

Applies to all users.

Method 5: Edit /etc/profile

Another system‑wide file, also requiring root:

# Make the file writable if needed
chmod -v u+w /etc/profile
vim /etc/profile
# Append at the end
export PATH=$PATH:/home/uusama/mysql/bin

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

Permanent.

Applies to all users.

Method 6: Edit /etc/environment

System environment file (requires root):

# Make the file writable if needed
chmod -v u+w /etc/environment
vim /etc/environment
# Append at the end
export PATH=$PATH:/home/uusama/mysql/bin

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

Permanent.

Applies to all users.

Understanding Linux Environment Variable Loading Order

The system loads variables from several files in a specific sequence, which determines which definitions take precedence.

Variable Classification

Variables are either user‑level (e.g., ~/.bashrc, ~/.profile) or system‑level (e.g., /etc/bashrc, /etc/profile, /etc/environment).

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

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

When a user logs in, the system reads ~/.bash_profile (or ~/.profile); if absent, it reads ~/.bash_login, and then processes ~/.bashrc.

Testing the Loading Sequence

To observe the order, add a test variable UU_ORDER to the first line of each file, appending the file name:

export UU_ORDER="$UU_ORDER:~/.bash_profile"

After saving, open a new terminal and run echo $UU_ORDER:

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

The observed loading order is:

/etc/environment

/etc/profile

/etc/bash.bashrc

/etc/profile.d/test.sh

~/.profile

~/.bashrc

Detailed File Loading

/etc/profile

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

# /etc/profile: system-wide .profile file for the Bourne shell (sh)
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 and sets a user‑specific PATH:

# if running bash
if [ -n "BASH_VERSION" ]; then
  # include .bashrc if it exists
  if [ -f "$HOME/.bashrc" ]; then
    . "$HOME/.bashrc"
  fi
fi

# set PATH so it includes user's private bin directories
PATH="$HOME/bin:$HOME/.local/bin:$PATH"

Note that ~/.profile is read once at login, while ~/.bashrc is read each time a new shell is started.

Additional Tips

You can create a custom environment file (e.g., uusama.profile) with multiple export statements and source it from ~/.profile to load project‑specific variables on each login.

Aliases can also be defined, such as alias rm="rm -i", and added to ~/.profile for convenient usage.