Master Linux Environment Variables: 6 Proven Configuration Methods

Linux Environment Variable Configuration

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

System: Ubuntu 14.0

Username: uusama

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

Reading Linux Environment Variables

Methods to read environment variables:

The export command displays all currently defined environment variables.

The echo $PATH command outputs the current value of the PATH variable.

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 search path for executable commands, separated by colons. Quotes are optional when using export.

Method 1: Using export PATH

Directly modify PATH with export to add the MySQL directory:

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

Effective immediately.

Effective only for the current terminal session; closes when the window is closed.

Applies only to the current user.

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

Method 2: Editing ~/.bashrc

Append the export line to 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.

Applies only to the current user.

If later files overwrite PATH, this setting may be ignored.

Method 3: Editing ~/.bash_profile

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

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

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

Permanent.

Applies only to the current user.

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

Method 4: Editing /etc/bashrc

This system‑wide method requires root privileges:

# make the file writable if needed
chmod -v u+w /etc/bashrc

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

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

Permanent.

Applies to all users.

Method 5: Editing /etc/profile

Another system‑wide file that also requires root privileges:

# make the file writable if needed
chmod -v u+w /etc/profile

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

Effective when a new terminal is opened or after running source /etc/profile.

Permanent.

Applies to all users.

Method 6: Editing /etc/environment

This file defines system‑wide environment variables and also needs root access:

# make the file writable if needed
chmod -v u+w /etc/environment

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

Effective when a new terminal is opened or after running source /etc/environment.

Permanent.

Applies to all users.

How Linux Loads Environment Variables

Linux reads configuration files in a specific order, and later definitions can overwrite earlier ones.

Classification of Environment Variables

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

System‑level files: /etc/bashrc, /etc/profile (or /etc/bash_profile), /etc/environment. The system first reads ~/.bash_profile (or ~/.profile), then ~/.bashrc if present.

Testing the Loading Order

To test 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:~/.bash_profile" After editing all files, open a new terminal and run echo $UU_ORDER:

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

The observed loading sequence is:

/etc/environment

/etc/profile

/etc/bash.bashrc

/etc/profile.d/test.sh

~/.profile

~/.bashrc

Detailed File Loading Explanation

System files are read first, followed by user files. Opening /etc/profile shows it loads /etc/bash.bashrc and then scripts in /etc/profile.d. The ~/.profile file subsequently sources ~/.bashrc. The ~/.profile is read once at login, while ~/.bashrc is read for each new shell.

# /etc/profile: system‑wide profile file for Bourne‑compatible shells
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
if [ -n "BASH_VERSION" ]; then
  if [ -f "$HOME/.bashrc" ]; then
    . "$HOME/.bashrc"
  fi
fi
PATH="$HOME/bin:$HOME/.local/bin:$PATH"

Some Handy Tips

You can create a custom environment file (e.g., uusama.profile) with a series of export statements and source it from ~/.profile to make the variables available on every login.

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