# Debian Filesystem

Debian follows the **Filesystem Hierarchy Standard (FHS)**, a standard layout for Linux filesystems. Understanding the directory structure helps you find files, configure systems, and write portable scripts.

Key directories:

- `/bin`, `/usr/bin` — executable programs (built-in commands and utilities)
- `/sbin`, `/usr/sbin` — system programs (usually require root)
- `/lib`, `/usr/lib` — libraries and shared objects
- `/etc` — system configuration files (editable)
- `/home` — user home directories (e.g., `/home/alice/`)
- `/root` — root user's home directory
- `/tmp` — temporary files (cleared on reboot)
- `/var` — variable data: logs (`/var/log`), cache (`/var/cache`), databases
- `/opt` — optional third-party software
- `/usr/share` — documentation, data files, locale files
- `/usr/local` — locally compiled software (doesn't get overwritten by package updates)

```bash
$ ls /                          # list root directories
$ df -h                         # show disk usage by filesystem
$ mount                         # show mounted filesystems
$ du -sh /var/log              # disk usage of a directory
```

Tip: Configuration files in `/etc` usually have `.dist` backups. Always back up `/etc` before making changes—it's your system's personality.