Master Linux Environment Variables: 6 Proven Configuration Methods and Loading Order

When installing custom software on Linux, configuring environment variables is essential; the article uses an Ubuntu 14.0 system with user uusama and a MySQL binary directory /home/uusama/mysql/bin as the example.

Reading Environment Variables

The commands export (to list all variables) and echo $PATH (to display the current PATH) are shown with sample output, illustrating that PATH is a colon‑separated list of directories.

Method 1: Direct export PATH

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

Effective immediately.

Only the current terminal session is affected; closing the window discards the change.

Applies solely to the current user.

Remember to append the existing $PATH to avoid overwriting previous entries.

Method 2: Edit ~/.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 the current user is affected.

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

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

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 for the user.

Only the current user is affected.

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

Method 4: Edit /etc/bashrc (system‑wide)

# Make the file writable if necessary
chmod -v 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.

Applies to all users.

Method 5: Edit /etc/profile (system‑wide)

# Make the file writable if necessary
chmod -v 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.

Applies to all users.

Method 6: Edit /etc/environment (system‑wide)

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

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

Permanent.

Applies to all users.

Loading Principle and File Classification

Environment variables are divided into user‑level (e.g., ~/.bashrc, ~/.profile / ~/.bash_profile) and system‑level files (e.g., /etc/bashrc, /etc/profile, /etc/environment). When a user logs in, the shell reads ~/.bash_profile (or ~/.profile), then ~/.bashrc. System files are processed earlier.

Testing the Loading Order

To verify the order, the same variable UU_ORDER is exported in the first line of each file, appending the file’s name. After reopening a terminal, echo $UU_ORDER yields:

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

From this result the loading sequence is inferred as:

/etc/environment

/etc/profile

/etc/bash.bashrc

/etc/profile.d/test.sh

~/.profile (or ~/.bash_profile)

~/.bashrc

Detailed File Loading

The /etc/profile script loads /etc/bash.bashrc and then iterates over /etc/profile.d/*.sh. Sample excerpt:

# /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

The ~/.profile script 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"

Additional Tips

Create a custom profile file (e.g., uusama.profile) with your own export statements and source it from ~/.profile for project‑specific variables.

Define command aliases such as alias rm="rm -i" in ~/.profile to make destructive commands safer.