Filesystem.pdf

8/18/2019 Filesystem.pdf

1/50

Class Meeting 3

LINUX BASED NETWORKS

Filesystem Hierarchy Standards & filesystem Structure Slide : 1

Linux Based Networks

Instructor: Zia-ul-Haq Ch.


2/50

Class Meeting 3



Today’s Agenda• File system Hierarchy Standard• Linux File System

– Comparison of MS-DOS & Linux.

– DOS to Linux Cheat Sheet.

– File Systems – File System Types

– Device Driver Names – Partitioning

– The mount command

– The UNIX File System Design


3/50

Class Meeting 3



Comparison of MS-DOS & Linux

In Linux path are separated

by ‘/’.

In Linux they are casesensitive

In Linux a dot is like anyother character in a filename.

In Linux, all file systems arepart of a single hierarchical treedescending from the root

directory ‘/’.

The directories in an MS-DOS

path are separated by ‘\’

In MS-DOS , file names arecase-insensitive

The dot in an MS-DOS filename separates the name part

from the extension.

In MS-DOS , each file systemresides on its own drive,

designated by ‘d:’.

LinuxMicrosoft


4/50

Class Meeting 3



In Linux , any file whoseexecute permission is turned on

is executable , regardless of itsname.

Linux file may have several

name , each represented bydifferent link.

In Linux you can set

permissions on a file.

In Linux , you must log in andprovide a password.

In MS-DOS , an executable fileis one with an extension of

.exe, .com, or .bat.

An MS-DOS , file has only onename.

In MS-DOS you can setattributes to make file readonly, hidden.

In MS-DOS you areautomatically connected to your system when you turn on

your system.

LinuxMicrosoft

Comparison of MS-DOS & Linux


5/50

Class Meeting 3



Many Linux commands you type at a shell prompt arenot that different from the commands you would typeeither in MS-DOS or in Windows (from the MS-DOS

prompt). In fact, some commands are identical.

DOS to Linux Cheat Sheet


6/50Class Meeting 3



DOS to Linux Cheat Sheet


7/50Class Meeting 3



File Systems

The file system is a combination of the partitions

and directories that make up your Linux system.

It is important to keep the file system healthy andorganized or you end up spending more timesearching for files and programs than actually

administering the system.


8/50Class Meeting 3



File System Types

• Depends on the configuration of kernel, LINUX can

support different types of FS (more than 20).

ufs UNIX File System, based on BSD Fat Fast File System (default).

hsfs High Sierra File System, used by CDROMs and supports Rock

Ridge extensions. Very similar to ufs, except that it does notsupport writable media or hard links. (iso9660)

nfs Network File System, the default distributed file system type

rfs Remote File Share, AT&Ts RFS product.

ext2 Second Extended File System. Common Linux file system.

proc Process Access File System, allows access to active processesand their images. This is not a real file system; instead, it's an

interface to the Linux kernel.msdos Used to access MS-DOS files from Linux.

swap swap partitions.

vfat

ufs UNIX File System, based on BSD Fat Fast File System (default).

hsfs High Sierra File System, used by CDROMs and supports Rock

Ridge extensions. Very similar to ufs, except that it does notsupport writable media or hard links. (iso9660)

nfs Network File System, the default distributed file system type

rfs Remote File Share, AT&Ts RFS product.

ext2 Second Extended File System. Common Linux file system.

proc Process Access File System, allows access to active processesand their images. This is not a real file system; instead, it's an

interface to the Linux kernel.msdos Used to access MS-DOS files from Linux.

swap swap partitions.

vfat


9/50Class Meeting 3



Samples of Device Driver Name

Device driver Drive

/dev/hda Master IDE drive, primary IDE bus.

/dev/hdb Slave IDE drive, primary IDE bus.

/dev/hdc Master IDE drive, secondary IDE bus.

/dev/hdd Slave IDE drive, secondary IDE bus.

/dev/sda First SCSI hard drive.

/dev/sdb Second SCSI hard drive.

/dev/st0 First SCSI tape drive./dev/scd0 First SCSI CD-ROM drive.

Device driver Drive/dev/hda Master IDE drive, primary IDE bus.

/dev/hdb Slave IDE drive, primary IDE bus.

/dev/hdc Master IDE drive, secondary IDE bus.

/dev/hdd Slave IDE drive, secondary IDE bus.

/dev/sda First SCSI hard drive.

/dev/sdb Second SCSI hard drive.

/dev/st0 First SCSI tape drive./dev/scd0 First SCSI CD-ROM drive.

nux


10/50Class Meeting 3



Partitioning

• For a large hard disk, it's better to split it intoseveral partitions (fdisk command):

• The root partition

– where / resides.

– Contains all the things necessaryto start the system, (50MB to 100MB)

• The swap partition

– Used to support virtual memory.

– The minimum size is equal to the size of RAM(or 16MB), while the maximum size is roughly 2x Physical memory.

– Linux can support more than one swap partitionand swap file.

/dev/hda1/dev/hda5

/dev/sda2

/dev/hda1/dev/hda5

/dev/sda2





A mount points is defined as the directory, such as "/" (root),under which a file system becomes accessible after beingmounted.

Mount Points





Understanding mounts

Mount points are directories where one may mount a

second disk partition to a first to make the second appearas part of the first.

That is, the tree receives a "graft," another branch, at thatpoint, and the tree thus becomes that much larger.

In fact, this is the only way to add to the existing filesystem's Volume, by adding another partition to it.





Understanding mounts

This additional partition could just as easily be an NFS(network file system) mount from another host across the

network , but would obviously only be available when thenetwork and the remote host were.



LINUX BASED NETWORKSr


Things to remember about mounts

Mount points must necessarily be directory names.

But the directories don't need to be empty.

No directory is truly empty, it contains at a minimum the"." and "..“

If a partition is mounted over an existing directory, thecontents of the existing directory become unavailable.

They can't be seen or used, and the disk space used bythose files is lost. The files in the disk partition mountedover it replace the original.





The mount command

Before a file system is accessible to the system, itmust be mounted on a directory.

– For example, if you have a file system on a floppy, youmust mount it under a directory, eg flp, in order toaccess the files on the floppy.

– After mounting the file system, all of the files in the filesystem appear in that directory.

– After unmounting the file system, the directory (in this

case, /flp) will be empty.

mount -t type device dir





Hard Drive Overview

As with other operating systems, the Linux kernel plus the

files associated with it are stored on a hard drive, which isa physical unit.

Within each hard drive are partitions, which functionsome what as virtual hard drive.

Inside each partition, you build a file system.


17/50


18/50

Class Meeting 3



File system Hierarchy Standard

(FHS)


19/50

Class Meeting 3



File system Structure

Red Hat is committed to the Filesystem HierarchyStandard (FHS), a document that defines the names andlocations of many files and directories.

The complete standard can be viewed at:

http://www.pathname.com/fhs/


20/50

Class Meeting 3



The Directory Tree Structure


21/50

Class Meeting 3



Overview of the FHS

This is where the Kernel is stored and LILO/GRUB gets itsinformation from, and where module information is stored.

Your best bet is to ignore this directory completely asfor a normal user , it is dangerous to play with

The /boot Directory


22/50

Class Meeting 3



The Root Directory ( / )

The root directory (/) of a Linux system is the directory thatcontains all other directories and files.

Other directories may be separately mounted and thus mayor may not be present at system startup.

Therefore, the file system that contains the root directorymust contain all files necessary to operate the system in

single-user mode.

The root directory also contains all files needed to shutdown and recover or repair the system.


23/50

Class Meeting 3



The Root Directory (cont….)

The following directories are essential and must be part ofthe root file system:

/bin, which contains binary files used by the systemadministrator and other users

/dev, which contains device files /etc, which contains host-specific configuration data

/lib, which contains system libraries

/sbin, which contains binary files used by the systemadministrator



24/50

Class Meeting 3



The Root Directory (cont….)

However, Linux systems typically include several otherdirectories, which may be used as mounting points for non-root file systems



25/50

Class Meeting 3



The /dev Directory

The /dev directory contains file system entries whichrepresent devices that are attached to the system. Thesefiles are essential for the system to function properly.

Device File DeviceConsol e System console

cua* Deprecated—originally referred to a serial port

f d* Floppy drive

hd* IDE hard disk or CD-ROM

l p* Parallel port md* RAID array

nul l Null output device

r amdi sk RAM disk

sd* SCSI hard disk

sr* SCSI CD-ROM s t* SCSI tape

t pqi c*, nt pqi c* QIC tape r f t * , nr f t *tty Terminal or pseudoterminal ttys* Serial port

vc* Contents of a tty device, such as a virtual consolezero Alt binary Os input device tty Serial port Contents of a tty



26/50

Class Meeting 3



The /etc Directory

The /etc directory is reserved for configuration files thatare local to your machine.



27/50

Class Meeting 3



Important Files in /etcF i l e C o n t e n t sa d j t i m e T i m e s y n c h r o n i z a t i o n d a t a

f d p r m F l o p p y d i s k p a r a m e t e r s

f s t a b F i l e s y s t e m t a b l e

g e t t y d e f s L o g i n t e r m i n a l c h a r a c t e r i s t i c s

g r o u p U s e r g r o u p s

i n i t t a b S y s t e m s t a r tu p c o n f i g u r a t i o n

1 d . s o . c o n f S y s t e m l i b r a r y c a c h e

l i l o . c o n f L i n u x l o a d e r c o n f ig u r a t i o nm o t d M e s s a g e o f t h e d a y

m t a b M o u n t e d f i l e s y s t e m t a b l e

n s s w i t c h . c o n f L i s t o f s q u r e e s f o r i n f o r m a t i o n o n u s e r s , h o s t s , n e t w o r k s , a n d s e r v i c e s .

m t o o l s . c o n f C o n f ig u r a t i o n o f m t o o l s u t i l i t i e s

p a s s w d U s e r a c c o u n t s

p r o f i l e S h e l l i n i t i a l i z a t i o n s c r i p t

s e c u r e t t y L i s t o f s e c u r e l o g i n t e r m i n a l ss h a d o w U s e r a c c o u n t _ e n c r y p t e d p a s s w o r d s , i f s h a d o w p a s s w o r d s e n a b l e d

s h e l l s L i s t o f a p p r o v e d s h e l l ss y s l o g . c o n f S y s t e m lo g c o n f ig u r a t io ne x p o r t s L i s t o f N S P e x p o r tsf t p * F T P c o n f i g u r a t i o n f i l e sh o s t . c o n f H o s t n a m e r e s o l u t io n c o n f ig u r a t i o n ( s e e a l s o r e s o l v . c o n f )h o s t s L i s t o f k n o w n h o s t s

h o s t s . a l l o w L i s t o f h o s t s a l l o w e d a c c e s s t o s e r v i c e sh o s t s . d e n y L i s t o f h o s t s d e n i e d a c c e s s t o s e r v i c e sh o s t s . e q u i v L i s t o f t r u s t e d h o s t sin e t d . c o n f C o n f i g u r a t i o n o f I n t e r n e t s u p e r - s e r v e r , i n e t dn e t w o r k s L i s t o f k n o w n n e t w o r k sp r in t c a p P r in t e r c o n f i g u r a t i o np r o t o c o l s L i s t o f k n o w n p r o t o c o l sr e s o l v . c o n f H o s t n a m e r e s o lu t i o n c o n f i g u r a t io n ( s e e a l s o h o s t . c o n f )r p c L i s t o f R P C s e r v ic e ss e r v i c e s L i s t o f T C P / I P s e r v i c e s



28/50

Class Meeting 3



Important Subdirectories of /etc

Subdirectory Contents

cron* Configuration of corn service

httpd Configuration of http (Web) servicepam.d Configuration of PAM, Red Hat's security librarypcmcia Configuration of PCMCIA slots and devices

ppp Configuration of PPP servicesrc.d System initialization filessecurity Security configurationskel User environment template filessysconfig System configurationXll X Window System configuration, including XF86 Config file



29/50

Class Meeting 3



The /lib Directory

This is where the basic libraries for booting Linux and runningstandard programs reside.

Do not delete anything in this directory, ever



30/50

Class Meeting 3



The /proc Directory

The /proc directory contains special files that either extract

information or send information to the kernel..

I would advise against deleting anything in thatdirectory.



31/50

Class Meeting 3



The /bin Directory

This is where basic shell commands such as ls and mvreside. This directory is always in the executable path.

The /bin directory contains binary files that are essentialto system operation in single-user mode.

These files are generally commands, which may be usedby the system administrator and by users.

Similar files not required for single user mode are placedin /usr/bin.



32/50

Class Meeting 3



Files in /bin

arch df igawk netstat sort ash dmesg ipcalc nice stty ash.static dnsdomainname kill nisdomainname su

awk doexec ksh ping sync basename domainname linuxconf PS tar bash echo In pwd tcsh bash2 ed loadkeys red touch

bsh egrep login remadmin true cat ex ls rm umount chgrp false mail rmdir uname chmod fgrep mkdir rpm userconf

chown fsconf mknod rvi usleep consolechars gawk mktemp rview vi cp gawk-3.0.3 more sed evie

And many more…………..



33/50

Class Meeting 3



The /sbin Directory

The /sbin directory is for executables used only by the rootuser. The executables in /sbin are only used to boot and

mount /usr and perform system recovery operations.

arp, clock, getty, halt, init, fdisk, fsck.*, ifconfig, lilo,mkfs.*, mkswap, reboot, route, shutdown, swapoff,

swapon, update



34/50

Class Meeting 3



The /usr Directory

This is an interesting one. When you install programs like theGIMP, and Window maker, they need to be accessed by allusers, so this is the directory they get installed into.



35/50

Class Meeting 3



The /var Directory

This is where your log files, and printer files are kept.



36/50

Class Meeting 3



The /home Directory

This is where your users have their accounts. If you haveadded any users other than your standard root account, theywill show up here. It can also house the directories than

your Web Server (Apache) accesses, if you have itinstalled.



37/50

Class Meeting 3



The /mnt Directory

This is the location where you mount your cdrom, zip drives,

or dos drives.



38/50

Class Meeting 3



The /opt Directory

If you have this directory, its probably where Netscape has

installed if you have chosen Netscape to be loaded. RedHat's Applix office suite also installs here.



39/50

Class Meeting 3



The /root Directory

This is main account directory. The root user have thisspace to keep all your downloads, and anything else you

want to keep in there basically



40/50

Class Meeting 3



The /tmp Directory

A useless directory, its short for Temporary. When you install

Linux first, it creates a file in your /tmp directory with all thedetails.

The /tmp directory contains temporary files andsubdirectories that are automatically deleted by thetmpwatch utility when they've not been used for a specifiedperiod of time (by default, 10 days).



41/50

Class Meeting 3



/lost+found: Recovered Files

When you recover a file system, files and file data may bepartially recovered. For example, the recovery utility mayrecover a file's data but not the file's name. Such files areplaced by the utility in the/lost+found subdirectory of the

root directory of the file system.



42/50

Class Meeting 3



• The root filesystem includes the root directory and aminimal set of files and subdirectories: – /boot for the kernel and boot up files;

– /dev for device files;

– /etc for configuration files (most important for SA);

– /sbin (or /bin) for important utilities and binary files (usually link

to /usr/bin);

• Recommended in separated partitions: – /usr for standard programs that are shareable across a whole site;

– /home for home directories of users;

– /var for spool directories, log files, accounting, etc.;

– /tmp for temporary files;

– /proc stores images of all running process

The Root and Standard Directories



43/50

Class Meeting 3

U S O S


Basic File system Concepts

The basis of the Linux Filesystem is firmly rooted in theproven concepts of the UNIX OS.

Files are represented as inodes, and directories are filescontaining a list of entries and devices accessible by requestingI/O on special files.



44/50

Class Meeting 3Filesystem Hierarchy Standards & filesystem Structure Slide : 44

Data Storage Layout in ext2Data within the ext2 file system is stored in a series of

identically sized data blocks.

These blocks are generally 1,024 bytes, though you canset them to be a different size while making a file

system.

• All this information is contained within a file system object

called an inode,



45/50


The UNIX File System Design

• The i-nodes – These are organized in a table format and

created when the file system is created.

– The inode contains more than 40 fields, such as

number of hard links, owner, group, mode, size,time stamps, type (regular, directory, special file,etc), pointers to location of data blocks, etc.

– Use chown, chgrp, touch commands to changesome of those information.



46/50


The UNIX File System Design

• The Super-block

– Its contains information on the size of the filesystem, the number of inodes, the number ofdata blocks, the free and used inodes, and theblock size for the file system.

– The superblock is kept in memory and in multiplelocations on disk for each file system.



47/50


Directories

Directories are structured in a hierarchical tree. Each directorycan contain files and subdirectories. Directories areimplemented as a special type of files.

Actually, a directory is a file containing a list of entries. Eachentry contains an inode number and a file name.



48/50

University of Lahore [email protected] 48


Steps in looking up a file

Looking up /home/pat/ch1.txtLooking up /home/pat/ch1.txt

i-node

number

(2 bytes)

6

Size

time

…

132

…

6 .

1 ..

19 user1

30 john

51 pat

26 peter

…

home directory

in block 132

51

Size

time

…

406

…

51 .

6 ..

64 notes

92 cgi

81 ch1.txt

17 doc

…

pat directory

in block 406

1 .

1 ..

4 bin

7 dev

14 lib

9 etc

6 home

8 tmp

…

root directory

81

Size

time

…

512

646

379

427

…

81

Size

time

…

512

646

379

427

…

data block (1kb)

i-node



49/50


Exercise:



50/50

Homework

• Homework this week:

• Next week:

Filesystem.pdf

Documents