File system discovery by mohamed elshawaf @devent 3

1. File System Discovery
BY
Mohamed Elshawaf

2. Question ?
•
What do you know
about
•
File System ?
•

3. What is file system ?
●
Method of storing and organizing computer files
and their data.
●
Essentially, it organizes these files into a
database for the storage, organization,
manipulation, and retrieval by the computer's
operating system.
Eg:- fat, ntfs, ext4, ext3.......

4. What is file system hierarchy ?

To put it simply, it can be visualized as
a tree with its roots and all.

At the top of the hierarchy is invariably
the root path which is represented by '/' and all other directories
are created beneaththis root path in linux.

5. Different from Windows
.Windows starts with drives, which are
•
explicit
•
– C:
•
– D:

6. 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.

7. Attention
•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.
•In Windows, case does not matter
•In Linux, everything is case sensitive.

8. Drives vs. directories
•In Windows, drives are directories
•In Linux, you can have several drives
•all under one overall directory

9. Standard?
•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

10. /
•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

11. Let’s
Zoooooooooooom

13. /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

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

15. /dev
•Kinda-sortaan equivalent to a mashup
of the Device Manager and
C:WindowsSystem in Windows
•Containsa file describing every device,
and these files can send data to each
device
•InLinux, everything is a file or a
directory

16. /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

17. /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

18. /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

19. /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

20. /etc/fstab
•Automatically mounts file systems
across multiple drives or partitions, or
even from remote systems
•Thisfile tells the system what drive to
access, and where to mount it in your
system

21. /etc/fstab
•Automatically mounts file systems
across multiple drives or partitions, or
even from remote systems
•Thisfile tells the system what drive to
access, and where to mount it in your
system

22. /etc/hosts
•This
is the famous hosts file, which
matches up names with IP addresses
•Thisis like level 1 DNS. The system
looks here first.
•Thiscan be used to block sites by
putting their URL in here

23. /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)

24. /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/

25. /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

26. /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/devmix
•This can contain configuration files for
applications that are user-specific

27. /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

28. 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

29. /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

30. /lib 2
•
•Also
in this directory are kernel
modules
•Other library locations for other
programs include /usr/lib and
/usr/local/lib

31. /media, /mnt
•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
•Most current distro versions will mount
these devices automatically

32. /opt
•Intended as a place for “optional”
software, i.e. add-on packages that are
not part of the default installation

33. /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
•Gosh, what would happen if you deleted
a file here?

34. /root
•Home directory for the root account
•Normally,you don't want to be root,
and you don't want to go here

35. /sbin
•Placefor System binaries
•One of three such directories
 – /sbin
 – /usr/sbin
 – /usr/local/sbin
•Allthree hold utilities used for system
administration, and are intended for the
root user like for booting, restoring,
recovering, and/or repairing the system

36. /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

37. /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

38. /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

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

40. /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

41. /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

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

43. /usr/share/man
•Primary location for man pages for the
system

44. /usr/src
•Source code is placed here, for
reference purposes only
•Thisincludes the source code for the
Linux kernel

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

46. /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.

47. /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

48. /var/log
•
•Contains the log files generated by
programs

49. The end ☺