Linux: File system hierarchy

Quick How To Guide

In this tutorial is described Filesystem Hierarchy Standard (FHS), which specifies required directories. The root directory is "/" and it should contains only the subdirectories.

/bin

Contains binaries which can be executed from command line (ls, grep, mkdir...)
Programs that can be used by users (system, admin, normal users)
It can be in single-user mode

/boot

Contains everything required for the boot process
Kernel
Grant Unified Boot-loader
LILO (LInux LOader)

/sbin

Binaries
Program used by ssytem and admin
Normal users can used programs in /bin if they are allowed
Usually normal users does not have this directory in $PATH variable

/dev

Files of all devices
Created during installation operating system.
Create new devices: /dev/MAKEDEV

File	Description
sda	First SCSI drive on the SCSI/SATA bus
md0	First group of meta discs (RAID)
ttyS0	First serial port
lp0	First parallel printer
null	bin for bits
random	Deterministic random bits
urandom	Non deterministic random bits

/etc

File	Description
passwd	Users information
fstab	Partition and storage mounting information
rc or rc.d or rcX.d	Run commands - commands that runs when OS starts

/home

Home directory for users
All data and system settings of users
Can be divided to groups (school, office, financial)

/root

Home directory for user root
Normal users don't have permissions.

/lib

Libraries for programs
/lib/modules: kernel modules, network controls, file system control

/tmp

Temporary files
Used by running programs

/mnt

Mounting temporary file systems
File systems from /etc/fstab are mounted during start OS
Network file systems
/media: DVD, USB

/usr

Programs, libraries installed from OS distribution
Accessible for everyone

/usr/

Directory	Description
local	Software installed by admin on local device
X11R6	Files of Windows OS
bin	Almost all commands for users
sbin	Usually server's programs
include	Header files for C language
lib	Stable libraries

/usr/share/

Directory	Description
X11	Files of Windows OS
dict	Glossary
man	Manual pages
doc	Documentation
info	Information files
src	source files

/var

Contains files that are changed when OS is running.

Subdirectory	Description
log	Logging files
run	Run-time variable data
spool	Program using queue (mails, printers)
mail	Mailbox
local	variable data from /usr/local
lib	Holds dynamic data libraries/files
lock	Lock files. Indicates that resource (database, file) is in use and should not be accessed by another process.

/opt

Third-party software

/proc

Created by OS kernel
Information about system
Stored only in RAM
Does not use any disc space

Every process has subdirectory (by PID)

Subdirectory	Description
/PID/status	Stats about process
/PID/cmdline	How was process started and what input arguments
/PID/maps	Region of contiguous virtual memory in a process or thread
/PID/environ	Environment of process

Interesting files

File	Description
cpuinfo	Information about CPU
meminfo	Usage of memory
version	Kernel version
cmdline	Kernel's parameters from boot loader
devices	List of drivers for kernel
interrupts	Which interrupts are used and how many times
ioports	list of currently registered port regions used for input or output communication.
dma	ISA Direct Memory Access channel
kcore	image of physical system memory
cmdline	Kernel's parameters from boot loader
cmdline	Kernel's parameters from boot loader

/lost+found

Recovered or damaged data after crash.
Each partition has own /last+found directory

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