Master Linux Environment Variables: Quick Config & Loading Order Explained

Linux Environment Variable Configuration

When installing software manually, you often need to set environment variables. Below are several methods to configure them on Ubuntu 14.0 for user "uusama", adding the MySQL bin directory to PATH.

Reading Environment Variables

Use export to list all variables and echo $PATH to show the 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 contains colon‑separated directories; you can add new ones with or without quotes.

Method 1: export PATH directly

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

Effective immediately

Only for the current terminal session

Applies to the current user

Remember to include the original $PATH to avoid overwriting

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 for the current user

If later files overwrite PATH, this may not take effect

Method 3: Edit ~/.bash_profile

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

Effective on new terminals or after source ~/.bash_profile Permanent for the user

Only for the current user

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

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

# make 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 in new terminals or after source /etc/bashrc Permanent

Applies to all users

Method 5: Edit /etc/profile

# make 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 in new terminals or after source /etc/profile Permanent

Applies to all users

Method 6: Edit /etc/environment

# make 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 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, which determines which definition wins when the same variable appears multiple times.

Classification

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

System‑level files: /etc/bashrc, /etc/profile (or /etc/bash_profile), /etc/environment When a login shell starts, Bash reads ~/.bash_profile (or ~/.profile), then ~/.bashrc. System files are read earlier.

Testing Load Order

By adding a line export UU_ORDER="$UU_ORDER:/path/to/file" at the top of each file and echoing $UU_ORDER in a new session, the observed order is:

/etc/environment

/etc/profile

/etc/bash.bashrc

/etc/profile.d/test.sh

~/.profile

~/.bashrc

Detailed Loading Process

/etc/profile

loads /etc/bash.bashrc and then scripts in /etc/profile.d/*.sh. Afterwards, ~/.profile includes ~/.bashrc if it exists. The ~/.profile file is read once at login, while ~/.bashrc is read for each interactive shell.

Tips

Create a project‑specific file (e.g., uusama.profile) and source it from ~/.profile to load custom variables on each login.

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