Master Linux Environment Variable Configuration: Six Methods and Loading Order Explained

Linux Environment Variable Configuration

When installing custom software on Linux, you often need to add directories to the PATH or set other environment variables. The example below assumes an Ubuntu 14 system, user uusama, and a MySQL binary directory at /home/uusama/mysql/bin.

Reading Environment Variables

export

– displays all currently defined environment variables. echo $PATH – prints the current value of PATH.

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 where the shell searches for executable files; entries are separated by colons ( :). You can modify it with or without surrounding quotes.

Method 1: Direct export PATH Command

Append the MySQL directory to PATH directly in the current shell:

export PATH=/home/uusama/mysql/bin:$PATH   # prepend
# or
export PATH=$PATH:/home/uusama/mysql/bin   # append

Effective immediately.

Only affects the current terminal session.

Limited to the current user.

Remember to include the existing $PATH to avoid overwriting previous 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 for new terminals or after running source ~/.bashrc.

Permanent for the user.

May be overridden if later files modify PATH.

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

Similar to ~/.bashrc, but placed in the login‑profile file:

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

Effective after a new login session or after 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 append the export line:

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

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

Permanent for all users.

Method 5: Edit System File /etc/profile

Also requires root. The steps mirror Method 4:

# make writable if needed
chmod u+w /etc/profile
vim /etc/profile
# add at the end
export PATH=$PATH:/home/uusama/mysql/bin

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

Permanent for all users.

Method 6: Edit System File /etc/environment

This file is read by the PAM module at login. Add the export line similarly:

# make writable if needed
chmod u+w /etc/environment
vim /etc/environment
# add at the end
export PATH=$PATH:/home/uusama/mysql/bin

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

Permanent for all users.

How Linux Loads Environment Variable Files

Environment variables are divided into user‑level (e.g., ~/.bashrc, ~/.profile) and system‑level (e.g., /etc/bashrc, /etc/profile, /etc/environment) files. During a login, the shell reads files in a specific order, and later definitions can overwrite earlier ones.

Testing the Loading Order

To observe the order, add the same variable UU_ORDER to the first line of each file, appending the file name to its value: export UU_ORDER="$UU_ORDER:/path/to/file" After saving and opening a new terminal, run echo $UU_ORDER to see the concatenated list. The observed order is:

/etc/environment

/etc/profile

/etc/bash.bashrc

/etc/profile.d/test.sh (if present)

~/.profile (or ~/.bash_profile)

~/.bashrc

Detailed File Loading

/etc/profile

loads /etc/bash.bashrc and then iterates over /etc/profile.d/*.sh. The user’s ~/.profile (or ~/.bash_profile) subsequently sources ~/.bashrc. The ~/.profile is read once at login, while ~/.bashrc is read for each interactive shell.

# Example snippet from /etc/profile
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

# Example snippet from ~/.profile
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 file (e.g., uusama.profile) with your own export statements and source it from ~/.profile to keep project‑specific variables organized.

Define command aliases (e.g., alias rm="rm -i") in ~/.profile or ~/.bashrc for safer usage.