Master Linux Environment Variables: Permanent, User, and Temporary Settings Explained

What Are Linux Environment Variables?

Linux is a multi‑user operating system, and each user has a personal runtime environment defined by a set of environment variables. Modifying these variables lets you tailor the environment to your needs.

Permanent Variables for All Users

Variables placed in /etc/profile apply system‑wide, affecting every user. Only the root account can edit this file.

# vi /etc/profile
export CLASSPATH=./JAVA_HOME/lib:$JAVA_HOME/jre/lib

After editing, run source /etc/profile to apply changes immediately; otherwise they take effect at the next login.

Permanent Variables for a Single User

For user‑specific settings, add export lines to ~/.bash_profile (login shells) or ~/.bashrc (non‑login shells). Both files are hidden; list them with ls -a.

# vi /home/rethink/.bash_profile
export CLASSPATH=./JAVA_HOME/lib:$JAVA_HOME/jre/lib
source /home/rethink/.bash_profile

The two files differ: .bash_profile is read once at login, while .bashrc is read for each new terminal session.

Temporary Session Variables

Variables defined directly in the shell with export VAR=value exist only for the current session. They disappear when the terminal is closed or the user logs out.

$ export NAME="rethink"
$ echo $NAME
rethink

Common Commands for Managing Variables

echo – prints the value of a variable, e.g., echo $NAME .

export – creates or updates a variable, e.g., export NAME='rethink' .

env – lists all environment variables for the current user.

set – shows all shell variables, including user‑defined ones.

unset – removes a variable, e.g., unset NAME .

readonly – makes a variable immutable; unset will no longer affect it.

Frequently Used Environment Variables

PATH – colon‑separated list of directories searched for executable files. Example:

# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

To prepend the current directory:

$ pwd
/root/docker/httpd
$ export PATH=$PATH:$PWD
$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin:/root/docker/httpd

HOME – the user's home directory.

$ echo $HOME
/home/rethink

HISTSIZE – number of commands stored in history (default 1000).

$ echo $HISTSIZE
1000
$ HISTSIZE=1001
$ echo $HISTSIZE
1001

LOGNAME – the login name of the current user.

$ echo $LOGNAME
rethink

HOSTNAME – the system's host name.

$ echo $HOSTNAME
JDu4e00u53f7

SHELL – path to the user's default shell.

$ echo $SHELL
/bin/bash