- / Primary directory of the entire filesystem hierarchy
- /bin Essential executable programs that must be available in single user mode
- /boot Files needed to boot the system, such as the kernel, initrd or initramfs images, and boot configuration files and bootloader programs
- /dev Device Nodes, used to interact with hardware and software devices
- /etc System-wide configuration files
- /home User home directories, including personal settings, files, etc.
- /lib Libraries required by executable binaries in /bin and /sbin
- /lib64 64-bit libraries required by executable binaries in /bin and /sbin, for systems which can run both 32-bit and 64-bit programs
- /media Mount points for removable media such as CDs, DVDs, USB sticks, etc.
- /mnt Temporarily mounted filesystems
- /opt Optional application software packages
- /proc Virtual pseudo-filesystem giving information about the system and processes running on it. Can be used to alter system parameters.
- /run Run-time variable data, containing information describing the system since it was booted. Replaces the older /var/run
- /sys Virtual pseudo-filesystem giving information about the system and processes running on it. Can be used to alter system parameters. Similar to a device tree and is part of the Unified Device Model.
- /root Home directory for the root user
- /sbin Essential system binaries
- /srv Site-specific data served up by the system. Seldom used.
- /tmp Temporary files; on many distributions lost across a reboot and may be a ramdisk in memory.
- /usr Multi-user applications, utilities and data; theoretically read-only.
- /var Variable data that changes during system operation