/- 1st level./usr- 2nd level./usr/local- 3rd level.
The directories on each level usually repeat, e.g. /bin --> /usr/bin --> /usr/local/bin
/ - Root directory structure, everything is under root
├── /bin - Common system commands
├── /boot - Linux system boot files, anything necessary to boot up the system
├── /dev - Special device files
├── /etc - Configuration files for all proprams
│ └── /opt - Configuration files for binaries stored in /opt
├── /home - Users' home directory (example /home/george, /home/daniel, etc.)
├── /lib - System libraries
├── /media - Removable media mounts (e.g. cdrom, floppy, etc.)
├── /mnt - Temporary mounting points for devices (e.g. file system disks)
├── /opt - Optional packages by various software
├── /proc - Process and kernel info
├── /root - Home directory of the root user
├── /run - Runtime data, e.g. process PIDs
├── /sbin - System binaries essential for the system
├── /srv - Site-specific data (web scripts, ftp files, repositories)
├── /sys - Data about devices, kernel, etc.
├── /tmp - Temporary files, not preserved between system reboots
├── /usr - User data, usually read-only
│ ├── /bin - User binaries, not necessary for the system to work
│ ├── /lib - Libraries for user binaries
│ ├── /local - Local user data, specific to the host
│ │ └── /bin - Local user binaries, specific to the host
│ ├── /sbin - User services, daemons
│ └── /share - Shared data for user binaries
└── /var - Variable files that are expected to change
├── /cache - Cache data for various binaries
├── /lib - Data that's persisted by various binaries (e.g. databases)
├── /log - Various log files including system and non-essential binary logs
├── /run - Runtime variable data, usually a symlink to /run
└── /tmp - Temporary data that are usually preserved between reboots, unlike /tmp
Refs