Master Linux Environment Variables: Configuration, Loading Order, and Tips

Linux Environment Variable Configuration

When installing software manually, you often need to set environment variables. Below are several ways to configure them on Linux.

System: Ubuntu 14.04

User: uusama

Target: add MySQL bin directory /home/uusama/mysql/bin to

PATH

Reading Environment Variables

You can list all environment variables with export and display a specific variable with echo $PATH.

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 the shell searches for executable files, separated by colons.

Method 1: Using export PATH

Directly modify PATH in the current shell:

export PATH=/home/uusama/mysql/bin:$PATH

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

Effective immediately

Only lasts for the current terminal session

Applies to the current user

Remember to keep the original $PATH part to avoid overwriting existing entries

Method 2: Editing ~/.bashrc

Add 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 for the user

Only affects the current user

If later files overwrite PATH, the change may be lost

Method 3: Editing ~/.bash_profile

Similar to ~/.bashrc, add the export line to ~/.bash_profile (or ~/.profile if the former does not exist):

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

Only affects the current user

Method 4: Editing /etc/bashrc

System‑wide configuration requires root privileges:

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

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

Applies to all users

Method 5: Editing /etc/profile

Another system‑wide file, edited similarly to /etc/bashrc:

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

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

Applies to all users

Method 6: Editing /etc/environment

This file sets system‑wide environment variables. Edit it with root rights:

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

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

Applies to all users

How Linux Loads Environment Variables

Linux reads configuration files in a specific order. The order determines which definition wins when the same variable is defined multiple times.

Classification of Environment Variables

They can be divided into:

User‑level variables defined in ~/.bashrc, ~/.profile (or ~/.bash_profile)

System‑level variables defined in /etc/bashrc, /etc/profile (or /etc/bash_profile), and /etc/environment When a login occurs, the shell reads ~/.bash_profile (or ~/.profile), then ~/.bashrc, applying the values in that sequence.

Testing the Loading Order

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

export UU_ORDER="$UU_ORDER:/etc/bash_profile"

After logging out and back in, run echo $UU_ORDER to view the concatenated list, which reveals the loading sequence:

/etc/environment

/etc/profile

/etc/bash.bashrc

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

~/.profile

~/.bashrc

Detailed Loading Process

The system first processes /etc/profile, which may source /etc/bash.bashrc and scripts under /etc/profile.d/. Then ~/.profile is read, which in turn sources ~/.bashrc. The ~/.bashrc file is executed for each interactive shell.

# Example snippet from /etc/profile
if [ "$PS1" ]; then
  if [ -n "$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

Later, ~/.profile typically contains:

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

# Ensure user bin directories are in PATH
PATH="$HOME/bin:$HOME/.local/bin:$PATH"

Additional Tips

You can create a custom environment file for a specific project, e.g., uusama.profile, define variables there, and source it from ~/.profile with source uusama.profile. This makes the variables available on each login.

Aliases can also simplify commands, such as alias rm="rm -i", which can be added to ~/.profile for persistent use.