If you use Linux, it’s very helpful to know where important system files are stored. These folders control how your system runs, manages users, handles logs, and much more.
Here’s a quick and easy guide to the 10 most useful Linux directories and what they do 👇

1. /etc/passwd & /etc/shadow

These two files store user account details.

• /etc/passwd has info like username, user ID, and home folder.
• /etc/shadow stores encrypted passwords and password expiry settings.
  👉 Only the root user can view or edit /etc/shadow.

2. /etc/sudoers

This file controls who can run commands as root using sudo.
To edit it safely, always use: visudo

3. /etc/hosts & /etc/resolv.conf

These handle your computer’s network name settings.

• /etc/hosts maps IPs to names (like a mini local DNS).
• /etc/resolv.conf tells your system which DNS servers to use.

127.0.0.1   localhost
8.8.8.8     google.com

4. /etc/fstab

This file lists all the disks and partitions your system mounts automatically when it starts.
Example:

/dev/sda1  /  ext4  defaults  0  1

5. /var/log/

This folder contains system logs — records of what’s happening inside your system.
Common logs:

• syslog → general system messages
• auth.log → login and authentication logs
• dmesg → kernel messages

You can check logs using:

tail -f /var/log/syslog

6. /etc/network/interfaces or /etc/netplan/*.yaml

These files manage your network connections.
Older systems use /etc/network/interfaces, while newer ones (like Ubuntu 20+) use /etc/netplan/.

Example (Netplan):

network:
  version: 2
  ethernets:
    eth0:
      dhcp4: true

7. ~/.bashrc & ~/.bash_profile

These files store your custom commands and environment settings.
For example, you can set shortcuts (aliases) or add paths:

alias ll='ls -la'
export PATH=$PATH:/opt/bin

8. /etc/crontab & /var/spool/cron/

These files are used to schedule automatic tasks (cron jobs).
Example:

0 3 * * * /usr/bin/backup.sh

9. /var/www/

This is where web server files are stored — like your website’s pages and scripts.
Example:

/var/www/html/index.html

10. /etc/systemd/system/

This folder controls system services — programs that start automatically (like web servers or databases).
You can manage them using:

systemctl start nginx
systemctl enable mysql
systemctl status ssh