Linux Directory Structure

This presentation examines the way files are stored in Linux following the File System Hierarchy. It also addresses the recent proposals by Fedora to change this to merge bin directories.

1. Linux Directory Structure
Kevin B. O’Brien
Washtenaw Linux Users Group
http://www.lugwash.org

2. General Notes
●Linux derives from Unix and is designed
to be multi-user
●This explains some otherwise puzzling
choices
●This may have something to do with
Fedora proposing to change this
Directory Structure

3. Drives 1
●Linux derives from Unix
●Different from Windows
●Windows starts with drives, which are
explicit
–C:
–D:

4. Drives 2
●Linux does not make drives explicit.
●You can have one physical drive, several
physical drives, partition the drives into multiple
partitions, and normally you won’t be aware of
it.
●In a file manager, you won’t see drives, just
directories
●But if you look in fstab, you will see things like
hda1, hda2, sda1, sda2. These are logical
drives (either physical or from partitioning)

5. Root
●In Windows, every drive has its own root
–C:\ is the root of the C drive
●In Linux, there is only one root, no matter
how many drives you may have
–In Linux, / is the root
●Root is ambiguous in one respect, since it
can refer to the top of the file structure,
and is also the name of the Administrator-
type account in Linux.

6. Root 2
●For our purposes, we will refer to root as
the top of the file structure in this
presentation.

7. Comparison
/home/data
/var
•/boot
•/bin
•etc.
C:
D:
E:
F:
/
Disk
Partitions
Linux Windows
/home
root

8. Watch out for...
●Windows uses a backslash for
everything
●Linux uses a forward slash for
everything
●In Windows, the logical drive (e.g. C:) is
an important part of the directory
structure
●In Linux, logical drives don't mean
much. You can even mount a separate
physical drive under a directory that is
on another drive.

9. Watch out for 2
●In Windows, case does not matter. The
C:\Windows directory is the same as
the
c:\windows directory.
●In Linux, everything is case sensitive.
The convention in Linux is to use lower
case for most things, but the important
thing to remember is that /usr/bin is not
the same thing as /USR/BIN.

10. Drives vs. directories
●In Windows, drives are directories
●In Linux, you can have several drives all
under one overall directory, or nested
one in another in the directory structure.
●In Linux, you tell the file system where
you want a drive to appear by where it
is mounted. See fstab for more on this.

11. Where did this come from?
●This started with a Linux effort in August,
1993
●In 1996 some BSD folks decided it should
be expanded to all Unix-like systems
●This resulted in the Filesystem Hierarchy
Standard, which can be found at
http://www.pathname.com/fhs/pub/fhs-
2.3.html

12. Standard?
●Of course, many distros vary from this to
some degree, some (Gobo) reject it
entirely, and MacOS tends to substitute
more “readable” names, like Library in
place of lib, etc.
●Red Hat seems to be pretty faithful
http://www.redhat.com/docs/manuals/linux/
RHL-9-Manual/ref-guide/s1-filesystem-
fhs.html

13. Standard? 2
●Distros can vary, but so can programs
●When you install a program, it may not
follow the FHS in deciding where to
place its files
●So this presentation should be
considered a guide to how things more-
or-less ought to work, but YMMV

14. /
●This is the symbol for the root of the file
system in Linux
●Every directory is “under” root,
ultimately
●This is not the same as the user “root”,
which is the user with God-like powers
over the system
●The user “root” does have a directory,
called /root

15. /bin
●Contains many of the commands used on
the command line
●Examples include cat, chmod,dmesg, kill,
ls, mkdir more, ps, pwd, sed, su
●the above commands, and many others,
must be in /bin to meet the standard.
●Other commands can be optionally
included, such as tar. gzip, netstat, and
ping

16. /bin 2
●There are other commands that are not in
here
●They are part of the shell (e.g. cd)
●For most users, this will be bash, the
Bourne-Again Shell
●You can tell by looking at the man pages
●Commands in /bin will have their own man
page, commands in bash will have info in
the bash man page

17. /boot
●Contains files needed for boot
–kernel
–Grub menu (good to know if you are dual-
booting)
–Lilo boot sector backups
●Contains data that is used before the
kernel starts executing user-mode
programs

18. /dev
●Kinda-sorta an equivalent to a mashup
of the Device Manager and
C:\Windows\System in Windows
●Contains a file describing every device,
and these files can send data to each
device
●In Linux, everything is a file or a
directory
●We mean it. We really mean it.

19. /dev 2
●hda1, hda2, etc. are partitions on the
first physical IDE drive
●sda1, sda2, etc. are partitions on the
first physical SATA drive
●/dev/cdrom is the optical drive
●/dev/fd0 is the floppy drive, if you have
one
●/dev/dsp is the speaker device

20. Fun with /dev
●Try this command out:
cat /etc/lilo.conf > /dev/dsp
●The sound you will hear is the sound of
your /etc/lilo.conf file
●If you don't have /etc/lilo.conf, substitute
any other file you do have
●So, /dev/dsp is the speaker, and the
speaker is the file /dev/dsp.

21. More /dev fun
●The most famous device in /dev is the
ubiquitous /dev/null
●Anything sent to this device disappears
into a black hole, and reappears in
another galaxy, much to the puzzlement
of the Lizard people of Zorg in the
CmfR!&v Galaxy.

22. /etc
●Perhaps the most important to understand
●No binaries can be here, per the standard
●This is just for configuration files
●Examples include /etc/inittab, /etc/fstab,
/etc/passwd, /etc/hosts, /etc/x11,and
/etc/opt

23. /etc 2
●These files are generally text files and
can be edited using any text editor:
emacs or vi on the command line, or
whatever graphical equivalent (e.g.
gedit, kate) your desktop offers

24. /etc/inittab
●Describes what takes place at bootup
●Includes the runlevel of the system, and
which processes should be run at each
runlevel
●Linux has seven runlevels, from 0-6

25. /etc/fstab
●Automatically mounts filesystems
across multiple drives or partitions, or
even from remote systems
●This is where you would place an entry
if you added a hard drive
●This file tells the system what drive to
access, and where to mount it in your
system

26. /etc/hosts
●This is the famous hosts file, which
matches up names with IP addresses
●This is like level 1 DNS. The system
looks here first.
●This can be used to block sites by
putting their URL in here and mapping it
to 127.0.0.1. Great way to get rid of
Double-Click.

27. /etc/passwd
●This is the password file, but it contains
more: user name, user password, user
ID, group ID, home directory, and shell.
It can optionally contain the user's “real
name”
●Each user is on its own line
●Each user can select the shell they
want to use (most use bash these days)

28. /etc/opt/
●This is a directory for the configuration files
for each system application you install.
Each application gets its own subdirectory
under /etc/opt/
●System applications are not just for one
user, but for anyone logged in to the
system
●This is not mandatory, so see the man
pages or help for your application

29. /etc/x11
●Configuration directory for x11, which is the
display system for graphical interfaces in
Linux
●This can vary with different distros, so
again you need to check
●/etc/x11/xorg.conf is the configuration file
that lets you specify the resolutions your
monitor and graphics card can display, for
instance

30. /home
●This is where the home directories for
all of the “ordinary” users are located.
●The exception is root, which has its own
home directory, /root/
●Each user gets a directory with their
user name: e.g. /home/baracko
●This can contain configuration files for
applications that are user-specific

31. User-specific Configurations
●These files should be in the /home
directory, and should begin with a “.”
character (i.e. “dot files”)
●If more than one, the files should go
into a directory with a name that begins
with the “.” character (i.e. “dot
directory), and then the files should not
begin with a “.”

32. /home Partition?
●Your home directory is where you
would place all of your documents,
videos, MP3s, etc.
●It can get fairly large
●It is also the stuff you want to back up,
and you don't want to lose
●Putting it on its own partition, or even its
own physical drive, is not a bad idea

33. Reinstalling
●If you have a separate /home partition,
you can reinstall (or do a clean
upgrade) and still keep not only your
data, but many of your file
configurations
●Examples are Firefox bookmarks,
Thunderbird or Evolution e-mail settings
and mail files, etc.

34. /lib
●This is the location for shared library
files that are used by system programs
●Shared library files are equivalent to
Windows' “*.dll” files
●The files here are intended to be
libraries for programs in /bin and /sbin,
i.e. needed to boot the system and run
the commands in the root file system

35. /lib 2
●Also in this directory are kernel modules
●Other library locations for other
programs include /usr/lib and
/usr/local/lib
●Generally these correspond to where
the binary is installed, i.e. a binary in
/usr/bin would put a library in /usr/lib,
and a binary in /usr/local/bin would put
a library in usr/local/lib

36. /media, /mnt
●This is one where there is no general
agreement
●Either directory can be a place to mount
removable media (e.g. CD, USB drive,
Floppy disk)
●/mnt is the older way, and is still used for
temporarily-mounted file systems
●At one time, these devices were often
mounted in the root directory, but that is
less common today

37. /media, /mnt 2
●Either directory is allowed by the standard
●Most current distro versions will mount
these devices automatically
●When they are mounted, an entry will go in
the directory
●For USB devices, you want to safely
unmount before removing. Current
graphical file managers let you do so in the
directory (right-click on the device).

38. /mnt vs. /etc/fstab
●The distinction is temporary vs.
permanent
●A file system that will be permanently
mounted should get an entry in fstab
●A file system mounted temporarily will
get an entry in /mnt when you mount it
●Again, everything in Linux is a file or a
directory. If you mount something on
the command line, a file is created in
/mnt.

39. /opt
●Intended as a place for “optional”
software, i.e. add-on packages that are
not part of the default installation
●Intended for use by sysadmins doing
something locally, not for software
developers creating packages
●Treat this as something deprecated, but
possibly still there.

40. /proc
●Have we mentioned that everything in
Linux is a file or a directory?
●Any time a process is created in Linux,
a corresponding file goes in here
●Most users have no need to go here,
but you're an adult, do what you want
●Gosh, what would happen if you
deleted a file here?

41. /root
●Home directory for the root account
●Normally, you don't want to be root, and
you don't want to go here
●Give yourself a user account, and use
that for day-to-day stuff. It is much safer
that way.

42. /sbin
●Place for System binaries
●One of three such directories
–/sbin
–/usr/sbin
–/usr/local/sbin
●All three hold utilities used for system
administration, and are intended for the
root user

43. /sbin 2
●/sbin should have those utilities
essential for booting, restoring,
recovering, and/or repairing the system
●Programs used after /usr is known to be
mounted (i.e. when there are no
problems) go into /usr/sbin
●Locally installed sysadmin programs go
in /usr/local/sbin

44. /tmp
●Guess what this one is?
●Yes, temporary files are placed here
●Assume that anything in this directory
will be deleted whenever the system is
booted
●If you want to have your own temporary
directory and not lose files at reboot,
create one in your home directory,
i.e. /home/username/temp

45. /usr
●Lots of stuff in here
●Back in the mists of prehistory, these
were the user directories, equivalent to
what are now /home directories
●Now /usr is for shareable data
●Not intended for software packages, in
general

46. /usr/bin
●Contains executable files for many
Linux commands
●These are commands that are not part
of the core Linux operating system
●They would go in /bin
●Examples of commands in here: perl,
python

47. /usr/include
●General use include files, including
header files, for C and C++
programming languages

48. /usr/lib
●Contains libraries for the C and C++
programming languages
●Object files, libraries, and internal files
not intended to be executed directly by
users or shell scripts

49. /usr/local
●For use by System Administrator when
installing software locally
●Must not be over-written when system
software is updated
●Generally has same subdirectories
as /usr

50. /usr/sbin
●Non-essential standard system
binaries, i.e. utilities
●Essential utilities go in /sbin

51. /usr/share
●For read-only architecture independent
data files
●Intended to be shared across platforms
(e.g. i386, Alpha, PPC)
●Must not change
●If the contents are variable, go to /var
e.g. a game file in /usr/share/games
must be static. Game play logs go in
/var/games.

52. /usr/share/man
●Primary location for man pages for the
system

53. /usr/src
●Source code is placed here, for
reference purposes only
●This includes the source code for the
Linux kernel

54. /var
●This is for files that are expected to be
updated and changed
●This includes:
–mail directories
–print spool
–logs
–web sites

55. /var 2
●Because these can be written to
constantly, they can grow over time
●On a server, you may want to put /var
on its own partition to limit the growth
●This can also prevent the /var directory
from bringing down the server by using
up all of the drive space.

56. /var/lock
●Contains lock files
●These files prevent two users (or two
programs) from trying to access the
same data at the same time
●You may need to delete a lock file from
time to time

57. /var/log
●Contains the log files generated by
programs

58. Fedora Proposal
●You may have noticed a lot of /bin
directories in this strcuture
●So did Fedora developers Harald Hoyer
and Kay Sievers
●Their proposal is called /usr merge

59. What is /usr merge?
●Move all executables into /usr/bin
●Move all related libraries into either
/usr/lib or /usr/lib64, as needed

60. Problems with /usr merge
●LSB adheres to FHS
●Would break most shell scripts that (for
example) start #!/bin/sh or #!/bin/bash
●Would other distros go along? Doe
Fedora care if they do?

61. Some benefits to /usr merge
●Matches what Solaris does already
●Simplifies
●Easier to run multiple instances of OS
on different machines in a network. This
is particularly true with btrfs.