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Filesystem Hierarchy Standard

Linux follows the Filesystem Hierarchy Standard (FHS). There are no drive letters - everything starts from a single root /. All devices, network filesystems, and special interfaces are attached via mounting. This entry covers the directory layout and the "everything is a file" philosophy.

Key Facts

  • Single root / - no drive letters (C:, D:)
  • Case-sensitive filesystem
  • All physical devices, network mounts, virtual interfaces appear as files under the tree
  • Config files live in /etc, logs in /var/log, user data in /home

Standard Directory Layout

Directory Purpose
/ Root of filesystem tree
/bin Essential user binaries (ls, cp, mv, bash)
/sbin System binaries (iptables, reboot, fdisk)
/boot Kernel, initrd, GRUB bootloader
/dev Device files (hardware interfaces)
/etc System-wide configuration files
/home User home directories
/lib, /lib64 Shared libraries for /bin and /sbin
/media Auto-mounted removable devices (USB, CD)
/mnt Manual/temporary mount point
/opt Optional/third-party software
/proc Virtual FS: process and kernel info
/root Root user's home directory
/run Runtime data (PIDs, sockets) - cleared on reboot
/srv Service data (web, FTP)
/sys Kernel device/driver info
/tmp Temporary files - cleared on reboot
/usr User programs, libraries, documentation
/var Variable data: logs, mail, caches

Everything Is a File

Unix philosophy: devices, directories, pipes, sockets - all represented as files.

Symbol in ls -l Type
- Regular file
d Directory
l Symbolic link
b Block device (random access: HDD, SSD)
c Character device (sequential: terminal, keyboard)
p Named pipe (FIFO)
s Socket

Special Filesystems

Type Mount Purpose
procfs /proc Process info, kernel parameters (required by ps, top)
sysfs /sys Kernel device/driver info
tmpfs /tmp, /run RAM-backed, fast, cleared on reboot
devfs /dev Device files (managed by udev at boot)

Filesystem Types for Disk Partitions

  • ext4 - standard Linux default
  • ext3 - older journaling FS
  • XFS - high-performance, default on RHEL/CentOS
  • btrfs - modern: snapshots, compression, subvolumes
  • NTFS/FAT32 - Windows filesystems (read/write supported)

Virtual/Overlay Filesystems

  • VFS - kernel abstraction for uniform FS access
  • NFS - mount remote filesystem over network
  • AUFS - merge multiple filesystems (used by Docker)
  • EncFS - transparent file encryption

Disk Usage Commands

df -h                    # mounted filesystems and space usage
df -h /home              # specific mount
du -sh /var/log          # total size of directory
du -h --max-depth=1 /    # size per top-level directory
lsblk                    # list block devices

Archive Utilities

# tar
tar -czf archive.tar.gz dir/         # create gzip archive
tar -xzf archive.tar.gz              # extract
tar -tf archive.tar.gz               # list contents

# zip
zip -r archive.zip dir/
unzip archive.zip
unzip -l archive.zip                  # list contents

Gotchas

  • /tmp has sticky bit by default - everyone can write, but only file owners can delete their own files
  • /proc files have size 0 in ls but contain data when read (generated on the fly by kernel)
  • /run vs /var/run: /run is tmpfs (cleared on reboot), /var/run may persist
  • /home is often a separate partition - reinstalling OS preserves user data

See Also