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In this guide, you’ll learn how to configure and maintain environment variables and login scripts that apply to all users on a Linux system. We’ll cover:
  • Understanding and viewing environment variables
  • Persisting system-wide variables via /etc/environment
  • Executing commands at login with /etc/profile.d/

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Understanding Environment Variables

Environment variables are key–value pairs that shells and applications use to adjust behavior. You can list the current environment with either env or printenv.
CommandDescriptionExample Output
envDisplays all environment variablesPATH=/usr/local/bin:…
printenv HOMEShows the value of a specific variable (HOME in this case)/home/aaron
# List all environment variables
$ env
PATH=/home/aaron/.local/bin:/home/aaron/bin:/usr/local/bin:/usr/bin
HISTSIZE=1000
GJS_DEBUG_TOPICS=JS ERROR;JS LOG
SESSION_MANAGER=local/unix:@tmp/.ICE-unix/2260

# Show HOME directory
$ printenv HOME
/home/aaron
To modify a variable for your current session, simply reassign it: 
# Increase Bash history size for this session
$ HISTSIZE=2000
$ echo $HISTSIZE
2000
You can reference variables in scripts. For example, create a file in each user’s home directory: 
$ touch "$HOME/saved_file"
This ensures the file lands in the right directory regardless of username.

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Setting System-Wide Environment Variables

While individual users often tweak ~/.bashrc, you can enforce variables globally by editing /etc/environment: 
$ sudo vim /etc/environment
Append lines in the format KEY="value": 
KodeKloud="https://www.kodekloud.com"
Save and log out, then back in to apply changes: 
$ echo $KodeKloud
https://www.kodekloud.com
The file /etc/environment only supports simple KEY="value" assignments. You cannot use shell expansions or commands here.

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Running Commands at Login

To execute scripts for every user at login, place them in /etc/profile.d/. For example, to record the last login timestamp: 
$ sudo vim /etc/profile.d/lastlogin.sh
Add: 
# Log the last login time into a file in the user’s home
echo "Your last login was at:" > "$HOME/lastlogin"
date                       >> "$HOME/lastlogin"
Scripts in /etc/profile.d/ are sourced by login shells automatically—you do not need a shebang (#!/bin/bash). 
# After logging out and back in
$ cat $HOME/lastlogin
Your last login was at: Thursday DEC 16 11:19:27 CDT 2021
Avoid syntax errors in /etc/profile.d/ scripts. A malformed script can prevent users from logging in properly.

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Further Reading & References

In the next article, we’ll explore advanced shell initialization techniques, including per-shell configuration and custom prompts.

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