# 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.