Primary hierarchy root and root directory of the entire file system hierarchy.
What is / ?
100
This directory contains the kernel and boot files. E.g. GRUB
What is /boot ?
100
Users' home directories, containing saved files, personal settings, etc.
What is /home ?
100
This directory contains the system configuration files.
What is /etc?
100
Default location for personal data and profile of the root user
What is /root?
200
This directory serves as a mount point for removable media devices such as CD-ROM's, digital cameras, and various usb-attached devices.
What is /media?
200
It contains variable data, such as logs, news, mail spool files and so on which is constantly being modified by various programs running on your system.
What is /var?
200
This directory contains the shared program libraries.
What is /lib?
200
This directory contains files that define and point to the system devices. It allows user
programs to access hardware devices on the system through the kernel. They are not data files,
but look like files from the OS's point of view.
What is /dev?
200
Secondary hierarchy for read-only user data; contains the majority of (multi-)user utilities and applications.
What is /usr?
300
Log files. Various logs.
What is /var/log?
300
It can be considered a black hole; it has unlimited storage, but nothing can be retrieved from it.
What is /dev/null ?
300
Temporarily mounted filesystems.
What is /mnt?
300
This directory typically contains spool directories for mail and cron, but also serves as a parent directory for other spool files (for example print spool files).
What is /var/spool ?
300
Mailbox files. In some distributions, these files may be located in the deprecated /var/spool/mail.
What is /var/mail?
400
Contains information about devices, drivers, and some kernel features.
What is /sys?
400
This virtual directory contains status information. "Virtual" means that no actual disk space is
associated with the file system; it is entirely contained in memory.
What is /proc?
400
This directory contains libraries that are not directly executed by users or scripts.
e.g.
4Suite
ao
apt
arj
aspell
avahi
bonobo
What is /usr/lib?
400
It contains any binaries that aren't required for repairs & booting.
What is /usr/bin ?
400
This virtual file contains information about the CPU. It's located in /proc directory.
What is /proc/cpuinfo ?
500
Tertiary hierarchy for local data, specific to this host. Typically has further subdirectories, e.g., bin/, lib/, share/
What is /usr/local?
500
A typical first file to check when troubleshooting on Red Hat (and derivatives). By default this file will contain information on what just happened to the system. The file is called /var/log/syslog on Debian and Ubuntu.
What is /var/log/messages?
500
Site-specific data served by this system, such as data and scripts for web servers, data offered by FTP servers, and repositories for version control systems
What is/srv ?
500
This file tells the Red Hat Setup Agent not to run at boot time. If you want to run the Red Hat Setup Agent at the next reboot, then simply remove this file
What is /etc/sysconfig/firstboot?
500
Run-time variable data: Information about the running system since last boot.