Download Linux Administration

T.Y. B.Sc. (IT) : Sem. V
Linux Administration
Time: 2½ Hrs.]
Prelim Question Paper Solution
[Marks : 75
Q.1
Attempt any TWO:
[10]
Q.1(a) What is Boot Strapping? Explain with the help of a diagram.
[5]
(A)
Bootstrapping
 In operating systems, this term refers to the process in which a part of the operating
system is brought into the Main Memory, with the processor executing it.
 "Bootstrapping" means starting up your computer. It involves all those stages, from the
moment you power on your machine till the system is ready to log in.
 6 Stages of Linux Boot Process (Startup Sequence)
The following are the 6 high level stages of a typical Linux boot process.
BIOS
 BIOS stands for Basic Input/Output System
 This is the first program to start when the machine is turned on.
 This is stored on the ROM on the computer’s chip.
 It does the POST (Power on self test).
 It checks for the functioning of the basic hardware of the system and displays the
messages accordingly.
 It looks for the MBR(Master Boot Record) in cd-rom, or hard drive. You can press a key
(typically F12 of F2, but it depends on your system) during the BIOS startup to change
the boot sequence.
 Once the MBR program is detected and loaded into the memory, BIOS gives the control
to it.
 So, in simple terms BIOS loads and executes the MBR which stores the boot loader.
MBR
 MBR stands for Master Boot Record.
 It is located in the 1st sector of the bootable disk. Typically /dev/hda, or
/dev/sda(sda1,sda2,sda3 are the partions on the hard disk)
 MBR is less than 512 bytes in size.
 It contains information about GRUB (or LILO in old systems).
 So, in simple terms MBR loads and launches the GRUB boot loader.
GRUB
 GRUB stands for Grand Unified Bootloader.
 The bootloader is the software program.
1
Vidyalankar : T.Y. B.Sc. (IT)  Linux
If you have multiple kernel images installed on your system, you can choose which one to
be executed.
 GRUB displays a splash screen, waits for few seconds, if you don’t enter anything, it
loads the default kernel image as specified in the grub configuration file.(grub.conf in
/boot)
 GRUB has the knowledge of the filesystem (the older Linux loader LILO didn’t
understand filesystem).
 Grub configuration file is /boot/grub/grub.conf (/etc/grub.conf is a link to this). The
following is sample grub.conf of CentOS.
Kernel
 Kernel uncompresses itself first.
 This initially makes the hardware running
 Mounts the root file system.
 initrd is used by kernel as temporary root file system until kernel is booted and the real
root file system is mounted.
 Now initial ramdisk is not required, so initrd goes away as we have the real disk now.
 It also contains necessary drivers compiled inside, which helps it to access the hard
drive partitions, and other hardware.
 Login form is provided at this step.
 Now the control is transferred to Init in /sbin directory of FHS.
 Kernel executes the /sbin/init program
 Since init was the 1st program to be executed by Linux Kernel, it has the process id
(PID) of 1. (Extra - ‘ps -ef | grep init’ and check the pid.)
Init
 Looks at the /etc/inittab file to decide the Linux run level.
 Following are the available run levels
 0 – halt
 1 – Single user mode
 2 – Multiuser, without NFS
 3 – Full multiuser mode
 4 – unused
 5 – X11(full GUI based multiuser mode)
 6 – reboot
 Init identifies the default initlevel from /etc/inittab and uses that to load all
appropriate program.
 Id:5:initdefault (mentioned in the inittab file)
 Execute ‘grep initdefault /etc/inittab’ on your system to identify the default run level
 Typically you would set the default run level to either 3 or 5.
 Based on the number specified in the initdefault parameter of inittab file, the
corresponding rcN.d file in /etc is executed.
Runlevel programs and rc scripts
 When the Linux system is booting up, you might see various services getting started.
For example, it might say “starting sendmail …. OK”. Those are the runlevel programs,
executed from the run level directory as defined by your run level.
 Following are the available run levels
 0 – halt
 1 – Single user mode
 2 – Multiuser, without NFS
 3 – Full multiuser mode
 4 – unused
 5 – X11(full GUI based multiuser mode)
 6 – reboot

2
Q.1(b) What is RAID? What are its different types? What are different levels of RAID?
(A)
RAID :
 Is an acronym for Redundant Array of Independent Disks?
 Used for maintaining copy of the data.
[5]
There are two types of RAID – hardware RAID and Software RAID.
Hardware RAID – in H. RAID, the disks have their own RAID controller with built in software
that handles RAID disk setup. The controller is a card in one of the system’s expansion slots.
Or it may be built onto the system board. The O/S does not control the RAID level used, it is
controlled by the hardware RAID controller.
Software RAID – there is no RAID controller card. The O/S is used to set up a logical
array and the O/S controls the RAID level used by the system.
Six RAID levels are commonly used.
The three most commonly used RAID levels are
 RAID level 0 – stripping
This level requires at least two disks and uses a method called
striping that writes data across both drives. There is no redundancy
provided by this level of RAID, since the loss of either drive makes
it impossible to recover the data. This level does give a speed
increase in writing to the disks.
 RAID level 1 – Mirroring
This level requires at least two disks and uses a method called
mirroring. With mirroring, the data is written to both of the drives.
So, each drive is an exact mirror of the other one and if one fails the
other still holds all the data. There are two variants to level 1 with one
variant using a single disk controller that writes to both disks. The
other variant uses two disk controllers, one for each disk. This variant
of RAID level 1 is known as duplexing.
 RAID level 2 – Error Checking and Correction
Requires minimum 3 disks. RAID 2 adds error checking and correcting checksums to
RAID-1. ECC is Error correcting code in which each data signal confirms to specific
rules of construction so that departures from this construction in the received signal
can generally be automatically detected and corrected.
RAID 2
A1
B1
C1
D1
Disk 0

A2
B2
C2
D2
Disk 1
A3
B3
C3
D3
Disk 2
A4
B4
C4
D4
Disk 3
Ap1
Bp1
Cp1
Dp1
Disk 4
Ap2
Bp2
Cp2
Dp2
Ap3
Bp3
Cp3
Dp3
Disk 5
RAID level 3 – Byte-Level Striping with Parity Disk
Requires minimum 3 disks. It does striping, like
RAID-0, but at a very small granularity. It also
adds parity disks which helps in error detection and
recovery.
Disk 6
RAID 3
A1
A4
B1
B4
A2
A5
B2
B5
A3
A6
B3
B6
Ap(13)
Ap(46)
Bp(13)
Bp(46)
Disk 0
Disk 1
Disk 2
Disk 3
Vidyalankar : T.Y. B.Sc. (IT)  Linux
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RAID level 4 – Block-Level Striping with Parity disk
requires minimum 3 disks. It attempts to add error
checking and recovery to RAID-3 by doing block
level striping with the addition of a single parity
disk.
RAID 4
A1
B1
C1
D1
A2
B2
C2
D2
A3
B3
C3
D3
Ap
Disk 0
Disk 1
Disk 2
Disk 3
RAID level 5 – Block-Level Striping with Distributed Parity
It requires at least three disks and uses striping to
write the data across the two disks similarly to
RAID 1. But unlike 1, this level uses the third disk
A1
B1
to hold parity information that can be used to
C1
reconstruct the data from either, but not both, of
Dp
the two disks after a single disk failure.
Disk 0
Bp
Cp
Dp
RAID 5
Ap
A2
B2
Cp
D1
A3
Bp
C2
D2
B3
C3
D3
Disk 1
Disk 2
Disk 3
The information of system’s RAID configuration is stored in /etc/traidtab .
Q.1(c) Draw and explain the architecture of a UNIX OS.
(A)
Shell
[5]
Applications
System calls
Kernel
Kernel
 It is the core/heart of the operating system. It interacts with hardware and most of
the tasks like memory management, task scheduling and file management.
Shell
 Shell is the utility that process your requests. A command typed in at the terminal, is
interpreted by the shell and calls the program that you want.
Applications
 Commands, utilities, File and Directories are covered.
 All files in UNIX are organized into a tree like structure called the filesystem.
 These are over 250 standard commands that come along with various options.
Q.1(d) Explain the features of Linux in detail with different Linux Distributions.
[5]
(A)
Features of Linux
 Multiuser : Linux system can support from 1 to 1000 users. It supports several users to
login on the same machine at the same time.
4
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Multitasking : Linux is a full multitasking system, and each user can run a different set
of programs and use all of the system resources simultaneously.

Multithreading : Linux has native kernel support for multiple independent threads of
control within a single process memory space.

Multiplatform : Linux runs on many different CPUs that means, it supports
multipropcessor machine.

Multipprocessor : Linux allows dynamic assignment of a program to one or two or more
computers or can involve multiple computers working on the same program at the same
time.
Different Linux distributions :
1) Debian : It is used as a base for many other distributions. It provides security. Debian
foundation is based on Open-Source philosophy with privilege to repositories containing
thousands of software packages ready for installation and use. Debian focuses mainly on
three branches : Stable(latest release), Unstable (branch that is in perpetual evolution)
and testing (next release to be).
2) Ubuntu : refers to a distribution based on unstable branch of Debian distribution, which
facilitates with best looking desktops. It encompasses features like hardware
compatibly and eases of installation, fast release cycle, up to date and various packages.
3) Fedora : comes with efficient graphical interface, strong corporate backing and
configuration tools. It serves as a general purpose distribution and is suitable for both
server as well as desktop applications, as this distribution is tailored with different
apps and functionality.
Q.2
Attempt any TWO:
[10]
Q.2(a) How is DHCP client configured? Explain.
[5]
(A)
Configuring the DHCP client
 Be sure that the NIC is properly configured and recognised by the system.
 Then tell the system that the IP information is to be obtained by the DHCP server by
doing the following steps –
 Open the file - /etc/sysconfog/network-scripts/ifcfg-eth0 in the editor.
 Find the BOOTPROTO = static.
 Change static to dhcp.
 Save the changes.
 Restart the network by issuing the command service network restart and the system
will receive its IP information from the DHCP server.
Q.2(b) State the number of subnets, subnet mask and number of hosts for Class B
subnets with 2, 3, 4 and 5 bits
(A)
No. of bits
No. of Subnets
Subnet mask
No. of hosts
2
4 = 22
255.255.192.0
16382
3
3
6=2
255.255.224.0
8190
4
8 = 24
255.255.240.0
4094
5
16 = 25
255.255.248.0
2046
[5]
Q.2(c) Explain the concept of NFS with suitable example.
[5]
(A)
 NFS is the most common method to share files across Linux networks.
 It is a distributed file system that enables local access to remote disks and file
systems.
Vidyalankar : T.Y. B.Sc. (IT)  Linux


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With proper network connection one can access files and directories that are physically
located on another system or even in a different city or country using standard Linux
commands.
It’s a common and popular file sharing protocol.
It follows standard Client/server architecture principles.
Server side
 The server component of NFS consists of the physical disks that contain the file
system one wants to share and several daemons that make these shared file systems
visible to and available for use by client systems on the network.
 When an NFS server is sharing a file system in this manner, it is said to be Exporting a
file system.
 Similarly, the shared file system is referred to as NFS Export.
Client side
 On the client side, an NFS client simply mounts the exported file systems locally.
 The mounted file system is known as an NFS Mount.
Example :
NFS server configuration and status files.

The server configuration file is /etc/exports, with the following format.
> dir host [options)]
wheredir is a directory or a file system to export,
host specifies one or more hosts permitted to mount dir,
options specifies one or more mount options.
Sample of /etc/exports file :
/usr/local/ *.linuxpracts.com (ro)
/home 192.168.0.0/255.255.255.0 (ro)
/var/tmp 192.168.0.1 (ro)
The
first
line
permits
all
hosts
with
the
name
of
somehost.linuxpracticals.com to mount /usr/local in read only format.
the
format
Configuring the NFS client :
Configuring a client system to use NFS involves
1) Making sure that the portmapper daemon is available.
2) The NFS file locking daemons –stated and locked are available.
3) Mounting the exports using the mount command.
Syntax :
mount -t nfs hostname:/file system mountpoint
Example :
mount –t nfs 192.168.0.1:/var/tmp exp1
Q.2(d) What are the general, server-specific and client-specific NFS security issues?
[5]
(A)
General NFS Security Issues
 /etc/exports file is one NFS weakness.
 If the cracker is able to take over a trusted address, the address listed in
/etc/exports, then the exported NFS mounts are accessible by the crackers.
 Another NFS weakness is a Normal NFS file system access controls that take over once
a client has mounted an NFS export: Once an NFS export has been mounted, normal
user and group permissions on the files take over access control.
 The first line of defence against these two weaknesses is to use host access control to
limit access to services on the system, mainly the portmapper, which is a target of
exploit attempt.
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Similarly, one should add entries in /etc/hosts.deny lockd,statd,mountd and rquotad.
Use of IP packet firewalls, using netfilter, increases NFS server security.
Server Security Issues
 On the server, always root_squash option in /etc/exports should be used.
 While root_squash in place, the server substitutes the UID of the anonymous user for
root’s UID/GID(0), meaning that a client’s root account cannot change files that only the
server’s root account can change.
 NFS also helps in maintaining a secure server through secure mount option, as this
mount option is one of the default option in mounted applies to all exports unless
explicitly disabled using insecure option
Client Security Issues
 On client, SUID (setUID) root program on NFS mounts should be disabled using the
nosuid option.
 This nosuid mount option prevents a server’s root account from creating an SUID root
program on an exported file system, logging in to the client as a normal user and then
using the UID root program to become root on the client.
 NFS versions 3 and 4 support NFS file locking.
 NFS clients must run stated and locked in order for NFS file locks to function
correctly.
 In summary, using TCP wrappers, the secure, root_squash and nosuid options and the
sturdy packet filters can increase the overall security of the NFS setup.
Q.3
Attempt any TWO:
Q.3(a) On a Linux machine a directory named/home/newusr/TYIT is to be accessed from
windows machine. Write the configuration to carry out this task.
(A)
[global]
workgroup = METRAN
encrypt passwords = yes
wins support = yes
log level = 1
max log size = 1000
read only = no
[homes]
browsable = no
map archive = yes
[printers]
path = /var/tmp
printable = yes
min print space = 2000
[10]
[5]
[test]
browsable = yes
read only = yes
path = /home/newusr/TYIT
Q.3(b) Distinguish between NFS and SAMBA Server.
[5]
(A)
The difference between Samba and NFS is primarily that Samba uses the SMB protocol
which is considered "standard" for PCs (Windows and OS/2 both have built in support for it,
a free client is also available for DOS, I'm not sure about MacOS), whereas NFS uses its
own protocol (usually just called "NFS") which is not commonly available for PCs (NFS clients
do exist for operating systems other than UNIX/Linux, but they're usually neither free or
easy to setup).
Vidyalankar : T.Y. B.Sc. (IT)  Linux
Samba's SMB protocol allows the server machine to handle authentication, so it can decide
what files the client has access to base on the particular machine and user connecting. NFS
by default trusts all client machines completely (it's really not intended to share files to
unsecured workstations) and lets the client machines handle authentication all on their own
(once an NFS server has been told to accept connections from a client machine the client
does not require any further server-side authentication, and can do anything it wants with
the filesystem NFS gives it access to). SMB does not (directly) support UNIX style file
permissions, so it is probably a bad idea to routinely use it to map filesystems between
machines which expect this information to be present and mutable, NFS of course supports
all standard UNIX file information (this also means that SMB is fine for accessing a UNIX
filesystem from a Windows machine, but not so hot the other way around). Network File
System (also known as NFS) is a protocol developed by Sun Microsystems. It allows a user
on a computer to access files that are sent across a network – similar to the way one
accesses local storage. It is most common in systems with a similar composition to the
UNIX system Samba is a re-implementation of SMB/CIFS networking protocol (meaning a
re-imaging of Server Message Block – or Common Internet File System). As with the NFS,
Samba runs most naturally on a system with qualities not unlike those of the UNIX systems.
It comes standard with almost every distribution of Linux, and is used as a basic system
service on all other UNIX-based systems. a. NFS is a protocol that allows a user to access
files over a network; Samba is essentially a re-imaging of the Common Internet File System.
b. NFS has four versions, the newest of which includes a stateful protocol; Samba has
multiple versions, the latest of which allows file and print sharing between multiple
computers.
NFS is developed from SUN Micro systems for file sharing Solaris/UNIX like system
samba is developed for sharing objects like file/printer between UNIX like system and
windows.
NFS is a way to mount remote file systems on an inode (UNIX) system so they look local.
Samba is a way to manage Windows network file systems on a Linux platform.
NFS is a protocol that allows a user to access files over a network; Samba is essentially a
re-imaging of the Common Internet File System.
NFS has four versions, the newest of which includes a stateful protocol; Samba has multiple
versions, the latest of which allows file and print sharing between multiple computers.
NFS is a protocol native to UNIX systems, while Samba is a program that provides SMB, a
protocol native to Windows systems. Linux supports both as file systems. From the point of
view of a Windows user, SMB may be the only available option. NFS isn't supported by
Windows without additional software.
Q.3(c) How are samba users created? Explain.
(A)
Creating samba users
 to use the samba server, samba users have to be created.
 On the command prompt, write the following commandsmbpasswd –a Kumar (where Kumar is a local user)
New SMB password:
Retype new SMB password:
Added user Kumar
Starting the samba server
Service smb start
8
[5]
Q.3(d) List NTP utility programs. Write purpose of any four.
(A)
NTP utility programs are as follows :
1) ntpdate
Sets the system date and time via NTP
2) ntpdc
Controls the htp daemon, ntpd
3) ntpkeygen
Generates public and private keys for use with NTP
4) ntpq
Queries the ntp daemon
5) ntprim
Provides ntp simulation for development and testing
6) ntptime
Displays the time variables maintained by Linux kernel.
7) ntptrace
Traces a chain of NTP servers back to the primary source.
8) tickadj
Sets certain time variables maintained by the Linux kernel.
[5]
Q.4
Attempt any TWO:
[10]
Q.4(a) What is zone file? Explain with suitable example.
[5]
(A)
Zone files contain resource records (RR) about IP addresses. Atypical zone file is shown in
A zone file can contain many types of RRs, which are listed in the order in
which they generally appear in the zone files, and explained next.
SOA — Start of Authority
The start of authority (SOA) is the first line in the zone file. The SOA identifies the name
server as the authoritative source for information about that domain. Each zone file has
only one SOA, and it contains the following data:
@ IN SOA main.tactechnology.com. mail.tactechnology.com.
(/2000052101 ; Serial
8h ;Refresh
2h ;Retry
1w ;Expire
1d) ;Minimum TTL
The first character in the SOA line is a special symbol that means “to look at this domain.”
IN means Internet. SOA means Start of authority. In this example, the authoritative
server for this domain is main .tactechnology.com., and mail.tactechnology.com. is the e-mail
address of the administrator. Note the trailing period after the domain names. If these are
not included, the domain name is appended to the entry. The opening parenthesis enables
the first line to be extended so that anything between the opening and closing parenthesis
is considered one line. The information within the parenthesis is passed to other name
servers, secondary masters that use this information to update their records. The line
containing 2000052101 ; Serial is the serial number of the file. Secondary servers compare
Vidyalankar : T.Y. B.Sc. (IT)  Linux
this number with their stored information. If the numbers are the same, the information
has not changed, and it is not necessary to download this file. If the serial numbers are
different, the file is downloaded to update the information in the secondary server. The
serial number can be any number desired as long as it can be incremented to indicate a
revision to the file. The semicolon indicates that what follows to the end of the line is a
comment.
Refresh — The amount of time the server should wait before refreshing its data.
Retry — The amount of time the server should wait before attempting to contact the
primary server if the previous attempt failed.
Expire — Means that if the secondary master is unable to contact a primary master during
the specified period, the data expires and should be purged.
TTL — Specifies the time to live for the data. This parameter is intended for caching name
servers and tells them how long to hold the data in their cache.
Q.4(b) State and explain E-Mail service and its components.
[5]
(A)
SMTP (pronounced as separate letters) Short for Simple Mail Transfer Protocol, a
protocol for sending e-mail messages between servers. Most e-mail systems that send mail
over the Internet use SMTP to send messages from one server to another; the messages
can then be retrieved with an e-mail client using either POP or IMAP. In addition, SMTP is
generally used to send messages from a mail client to a mail server. This is why you need to
specify both the POP or IMAP server and the SMTP server when you configure your e-mail
application.
POP3
 The full form is Post Office Protocol.
 This protocol is a part of email process.
 POP3 was developed to solve the problem of what happens to messages when the
recipient is not connected to the network.
 POP3 runs on a server that is connected to a network and that continuously sends and
receives mail.
 The POP3 server stores any messages it receives until the message recipient request
them.
 Without POP3, MUA and MTA cannot communicate.
 If one wants to read the mail, he needs POP3 to retrieve messages that arrive at his
MTA while he is offline.
 POP3 uses the MTA’s storage to hold messages until they are requested.
 When users want to check their email, they connect to the POP3 server and retrieve
messages that were stored by the server.
 After retrieval, the messages are stored locally and one can his MUA on his PC to read
them at his leisure.
IMAP4
 Full form – Internet Massage Access Protocol version 4.
 It provides much more sophisticated email-handling functionality than POP3 does.
 IMAP4 enables one to store email on a networked mail server.
 IMAP4 enables mail to reside permanently on a remote server, from which one can
access his mail.
 Mail retrieval can be done from any device, office PC, PDA, cell phone etc.
 The usual mail delivery process involves three components, a mail user agent (MUA), a mail
transfer agent (MTA) and a mail delivery agent (MDA).
Components :
 Mail user Agent
 To be able to send mail, users need a program called a mail user agent which is widely
referred to as mail client.
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The MUS provides users an interface for reading and writing email messages. Two types
of MUAs are available: those that have a graphical user interface(GUI) such as
thunderbird or Kmail, and those that have a command line interface(CLI), such as Mutt
or elm.
Whether MUA is GUI or CLI, the functionality is the same.
After composing an email message, the MUA sends it to a MTA which transmits the
message across the network.
Mail Transfer Agent
It is a program that sends the message across the network.
MTA works without any intervention by the user.
The MTA reads the information in the To: section of the email message and determines
the IP address of the recipient’s mail server.
Then the MTA tries to open a connection to the recipient’s server through a TCP/IP
port, typically port no 25. MTA queries.
MTAs query a domain’s DNS mail exchanger to determine the host that is responsible
for receiving mail for that domain.
If the MTA on the sending machine can establish a connection for the destination MTA,
it transmits the message using the SMTP.
Mail delivery Agent
After MDA receives the message from MTA, it stores the new message in the
recipient’s mail spool.
Mail spool is always identified by the recipient’s user name.
Q.4(c) Explain use of ssh, scp, sftp services.
[5]
(A)
ssh
 It is a secure shell program.
 It is used for logging into a remoter machine and executing commands in a remote
machine.
 It provides secure, encryptes communications between hosts.
 The host name to login should be specified.
 When the username is specified in the ssh command line, it demands for the password.
Example :
# ssh node5
Log on securely to node5.
# [email protected]
Log on to mylab.testra.edu as user user1.
scp
 This command securely copies files over the network.
Example : Putting of a single file –
# scp myfile1.dat mylab.textra.edu:data1.txt
Getting of a single file # scp mylab.textra.edu:data1.txt ./
It copiesnfile data1.text form your home directory of node4 to your current working
directory on your local server.
sftp
 Is used to transfer files to and from a remote computer.
 It is interactive and secure.
Vidyalankar : T.Y. B.Sc. (IT)  Linux

Once connected to the remote computer, giving a password if necessary, you can type the
following interactive commands to change directories and to transfer files between your
local computer and the remote computer.
get filename Retrieves remote file and stores it to local computer.
put filename Upload local file to store on remote computer.
cd path
Change remote directory to path
Ls
List remote files
Lls
List local files
lcd path
Change local directory to path
Quit
Quit sftp
Help
Display help text
Example :
# sftp 192.156.1.0
Enter password :
sftp> use the above commands.
#sftp [email protected]
Connect to mylab.testra.edu using username user1.
Q.4(d) Explain the files required to configure DNS server.
[5]
(A)
Examining Server Configuration Files
The three required files are
 named.conf — found in the /etc directory, this file contains global properties and
sources of configuration files.
 named.ca — found in /var/named, this file contains the names and addresses of root
servers.
 named.local — found in /var/named, this file provides information for resolving the
loopback address for the localhost.
The two files required for the master domain server are
 zone - this file contains the names and addresses of servers and workstations in the
local domain and maps names to IP addresses.
 reverse zone - this file provides information to map IP addresses to names.
1. /etc/named.conf
The named.conf file
 Commands are passed to the file in the form of statements.
 Seven configuration Statements can be used. These are listed here with a brief
explanation of their function.
options— lists global configurations and defaults
include— gets information from another file and includes it
acl— specifies IP addresses used in an access control list
logging— specifies log file locations and contents
server— specifies properties of remote servers
zone— specifies information about zones
key— specifies security keys used for authentication
2. The named.ca file
The first zone file is known as the cache file, and it references a file called named.ca,
which contains information about the world’s root name servers. This information
changes and needs to be updated periodically.
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3. The named.local file
The next zone file contains information about the localhost. The file referenced here is
named.local and contains information about the local domain.
4. Zone files
 The DNS zone file is text based database file that describes a portion of the
domain name system(DNS) called a DNS zone.
 A zone contains mapping between domain name and ip addresses and other resources
records (RR)
 Zone files contain resource records (RR) about IP addresses.
5. The reverse zone file
 The last zone file shown in the named.conf file is called tac.rev.
 This file is used to provide information for reverse lookups.
 Name also can be found out from an IP number, and this is called reverse address
resolution.
Q.5
Attempt any TWO:
[10]
Q.5(a) What are the features of Postfix Mail Server? Explain its primary configuration file.
[5]
(A)
 Postfix is a mail server that handles thousands and tens of thousands of messages per
day, so it probably provides all of the functionality needed.
Configuring Postfix
 Configuration file is /etc/postfix/main.cf.
 The mydomain variable specifies your domain name:
mydomain = example.com
 The myhostname variable identifies the local machine’s fully qualified domain name:
myhostname = coondog.example.com
 The myorigin variable identifies the domain name appended to unqualified addresses
myorigin = $mydomain
this causes all mail going out to have your domain name appended. Thus, if the value of
mydomain is possum_holler.com and your username is bubba, then your outgoing mail will
appearto come from bubba@possum_holler.com.


The mydestination variable tells Postfix what addresses it should deliver locally. For a
standalone workstation, which is a system that is connected directly to the Internet and
that has some sort of domain name resolution sunning, you want mail to that machine and
to localhost delivered locally, so the following entry should suffice:
mydestination = $myhostname, localhost, localhost.$mydomain
Postfix supports a larger number of configuration variables than the four just needed,
but these are the mandatory changes you have to make.
Create or modify /etc/aliases. At the very last, you need aliases for Postfix, postmaster
and root in order for mail sent to those addresses to get a real person.
postfix : root
postmaster : root
root : bubba
After creating or modifying the aliases file, regenerate the alias database using :
Postfix’s newaliases command:
#/usr/sbin/newaliases
You are ready to start postfix:
#service postfix start
Vidyalankar : T.Y. B.Sc. (IT)  Linux
Q.5(b) What are the files required for the configuration of VSFTPD? Explain.
(A)
Files
Description
/usr/sbin/vsftpd
This is the main vsftpd executable. It is the daemon
itself.
/etc/vsftpd/vsftpd.conf This is the main configuration file for the vsftpd
daemon. It contains many directives that control the
behavior of the FTP server.
/etc/vsftpd/ftpusers
Text file that stores the list of users not allowed to
log into the FTP server.
/etc/vsftpd/user_list
Text file used to either allow or deny access to users
listed. Access is denied or allowed according to the value
of the userlist_deny directive in the vsftpd.conf file.
/var/ftp
This is the FTP server’s working directory.
/var/ftp/pub
This serves as the directory that holds files meant
for anonymous access to the FTP server
[5]
Q.5(c) How to configure user level ftp access?
[5]
(A)
 To configure user level ftp access, /etc/vsftpd/ftpusers file is used.
 It contains the list of user or account names that are not allowed to log in using FTP.
 This file is used to increase security.
 For example, if a cracker somehow obtains the root password and tries to log in as root
using FTP, the login attempt will fail.
 This file is used to prevent privileged user accounts, such as root, from using FTP to
obtain access to the system.
 The following code shows the default /etc/vsftpd/ftpusers file
root
bin
daemon
adm
lp
sync
shutdown
halt
mail
news
uucp
operator
games
nobody
 So to prevent the username ‘bubli’ from logging in to the system via FTP, add ‘bubli’ to
the end of /etc/vsftpd/ftpusers.
Q.5(d) Explain any five parameters of vsftpd.conf file.
[5]
(A)
(i) anonymous_enable – allows or disallows anonymous FTP access.
anonymous_enable=YES/NO
(ii) write_enable – YES/NO – allows or disallows all variations of the FTP
commands that
allow FTP users to modify the file system.
(iii) chown_username – the user mentioned here is allowed to login via ftp.
chown_username=whoever
(iv) ftpd_banner - displays a site specific banner message when users connect to the
servers
ftpd_banner=”Welcome to FTP service”.
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(v) dirmessage_enable – through this, vsftpd displays the contents of a file named
.message.
dirmessage_enable=YES/NO
Q.6
Attempt any TWO:
[10]
Q.6(a) Explain the working of Apache web server.
[5]
(A)
How Web Servers Work?
 The Web client (a browser in this case) first performs a DNS lookup on the server name
specified in the URL, obtains the IP address of the server, and then connects to port
80 at that IP address (or another port if the server is not using the default HTTP
port).
 When the connection is established, the client sends an HTTP GET request for the
document in the URL, which could be, among other possibilities, a specific HTML
document, an image, a script, or a directory listing.
 After the server receives the request, it translates the document URL into a filename
on the local system.
For example, the document URL http://localhost/~kwall/news.html might become
/home/kwall/public_html/news.html.
 Next, Apache evaluates whether or not the requested document is subject to some sort
of access control and requests a user name and password from the client or rejects the
request outright, depending on the type of access control in place.
 If the requested URL specifies a directory (that is, the URL ends in /) rather than a
specified document, Apache looks for the directory index page, index.html by default,
and returns that document to the client. If the directory index page does not exist.
 Apache might send a directory listing in HTML format back to the client or send an
error message, depending on how the server is configured. The document can also be a
specially written script, a CGI (Common Gateway Interface) script. In this case, Apache
executes the script, if permitted to do so, and sends the results back to the client.
 Finally, after Apache has transmitted the requested document and the client receives
it, the client closes the connection and Apache writes an entry in one or more log files
describing the request in varying levels of detail.
Q.6(b) Write an SSI page that will display the long listing of the directory /home/tyit.
(A)
Create a new file having .shtml extension and place it in “/var/www/html/” directory.
<html>
<head>
SSI Test Page
</head>
<body>
<center>
SSI Test Page Output
<hr>
<p>
The listing of the directory /home/tyit - :
<p>
<!--#exec cmd="ls /home/tyit" -->
<hr>
</body>
</html>

SSI directive look like HTML comments. The general format is
<!-- #element attribute=value 
[5]
Vidyalankar : T.Y. B.Sc. (IT)  Linux
Q.6(c) Explain the files/etc/passwd and /etc/shadow and their fields.
[5]
(A)
/etc/passwd stores all the user details. Whenever a new user is created, an entry is made in
/etc/passwd. It stores the username, the user ID, group ID, the home directory and the
shell used by the user.
eg. logon : x: 501: 501: /home/logon:/bin/bash
/etc/shadow contains hashed (encrypted)
passwords for the users in /etc/passwd. The passwords are encrypted using md5 algo.
Q.6(d) How is virtual server configured? Explain virtual server configuration directives.
[5]
(A)
Virtual Servers
 The next section consists of the directives that are required to make settings for a
virtual hosts.
 It allows configurations through which web request is sent to different IP addresses or
hostnames and are handled by the same Apache Server process.
 Virtual hosts can be categorised in two forms
> IP bases virtual hosts
> Name based virtual hosts.
The virtual server configuration directiveDirective
Description
<virtualHostipaddr[:port]>
Defines the virtual host whose IP
address is addr.
<VirtualHost>
Default server
NameVirtualHostipaddr[:port]
Defines the IP address for an namebased virtual host.
ServerAliasltname
It enables the virtual server to respond
to one or more alternate hostnames when
used with name-based virtual hosts.
Starting and stopping Apache
#service httpd start
#service httpd stop
#service httpd restart
#service httpd reload
#service httpd configtest – to tell Apache to parsr its configuration files and display an
error message when detects any error.
Q.7
Attempt any THREE:
Q.7(a) State any 5 linux supported file systems and explain ext3 and ext 2.
(A)
5 Linux Supported File System
1. ext3
2. ext2
3. Reiser
4. FAT
5. NTFS
[15]
[5]
ext2(non-journaling file system)
 xt2 stands for second extended file system.
 ext2 does not have journaling feature.
 On flash drives, usb drives, ext2 is recommended, as it doesn’t need to do the over head
of journaling.
 Can handle file systems up to 4 TB
 It supports long file names up to 1012 characters.
 In case user processes fill up a file system, ext2 normally reserves about 5% of disk
blocks for exclusive use by root so that root can easily recover from that situation.
Ext3
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[2 marks]








Ext3 stands for third extended file system.
Starting from Linux Kernel 2.4.15 ext3 was available.
The main benefit of ext3 is that it allows journaling.
Journaling has a dedicated area in the file system, where all the changes are tracked. When
the system crashes, the possibility of file system corruption is less because of journaling.
(If no journaling, then fsck commend(file system consistency check) is used to check for
the corrupted file and to repair that file).
Under ext2, when a file system is uncleanly mounted, the whole file system must be
checked. This takes a long time on large file systems. ext3 keeps a record of
uncommitted file transactions and applies only those transactions when the system is
brought back up.
Maximum individual file size can be from 16 GB to 2 TB
Overall ext3 file system size can be from 2 TB to 32 TB
You can convert a ext2 file system to ext3 file system directly (without
backup/restore).
Q.7(b) What are the files required to be changed when we setup a new system or move
[5]
the system from one loction to another?
(A)
Whenever a new system is set up to work on a new network, a set of files needs to be
modified to get it working on new network.
1) Setting up the IP Address-/etc/sysconfig/network-scripts/ifcfg-eth0
 To set up the IP address on the network interface, the following file has to be changed
/etc/sysconfig/network-scripts/ifcfg-eth0
 Setting up the IP address on the network interface identifies the computer on the
network.
 Open the file /etc/sysconfig/network-scripts/ifcfg-eth0.
 Insert the interface’s IP address on the line that says
IPADDR= “ ”
 Check the following lines also.
BROADCAST=192.168.1.255”
NETMASK=”255.255.255.0”
DEVICE =”eth0”
BOOTPROTO=”static”
BROADCAST=192.168.1.255”
NETASK=”255.255.255.0”
NETWORK=”192.168.1.0”
ONBOOT=”yes”
USERCTL=no
 Once, the IP address is added, restart the network service by the command – “service
network restart”.
 Then check the changed ipaddress with the command - ifconfig.
2) Setting up the Hostname - Choose the host name.
It has to be added in two different places
/etc/sysconfig/network
/etc/hosts
In /etc/sysconfig/network HOSTNAME = “JERRY”
/etc/hosts Change the first line in the file by adding the host name
127.0.0.1
JERRY localhost:localdomain
And reboot the machine.
Vidyalankar : T.Y. B.Sc. (IT)  Linux
3)





Setting up the DNS Name resolution - resolv.conf.
The program that resolves hostnames to IP addresses reads a file called resolv.conf.
In this file DNS server’s IP address can be put with the name given to the server.
Multiple name servers can be added in this file. If one doesn’t respond , the control
shifts to the other host.
> nameserver1.2.3.4
> nameserver1.2.3.5
> nameserver1.2.3.6
On the local machine, try this with the ping command.
If the local machine’s address is 192.168.0.1 and the name given to it is “MyServer”,
then try to ping MyServer by the following command.
ping MyServer
4) Starting up network service from xinetd  In computer networking, xinetd (extended Internet daemon) is an open-source superserver daemon which runs on many Unix-like systems and manages Internet-based
connectivity.
 Xinetd is started on bootup and listens on ports designated in the /etc/xinetd.conf for
incoming network connections.
 Multiple network services, for ex, telnet, talk, etc. are stored in the file xinetd.d.
 One should disable any unnecessary services from being started from xinetd as a part
of securing the system. For example : telnet
 For example to disable telnet service, look in /etc/xinetd.d for a file telnet. And change
the following line
disable = no, and make it to yes to disable the telnet service.
 After the changes are saved, the xinetd service should be restarted by the following
command.
 Service xinetd restart
5) Starting up network services from the rc Scripts – /etc/rc3.d directory.
 Network services that are not started out of xinetd are started out of the rc scripts at
boot time.
 Network services started at the default boot level 3 are started out of the /etc/rc3.d
directory.
 This file has the names of the services to start or stop.
 The script to start the service starts either an S and the kill script starts with a K.
 For example, SSH is started from /etc/rc3.d/S55sshd and killed upon shutdown from
/etc/rc6/d/K25sshd.
Q.7(c) Explain the steps to configure caching proxy server on Linux.
(A)
The web proxy is called as Squid.
Configuring Squid
 The Squid configuration file is /etc/squid/squid.conf.
Key Squid Configuration Parameters
Parameters
Default values
Description
Cache_effective_group
Squid
Identifies the group Squid
runs as
Cache_effective_user
Squid
Identifies the user squid
runs as
Httpd_acce1_host
None
Defines the hostname of the
real HTTP server
Httpd_accel_with_proxy
Off
Controls whether Squid runs
as both an cache and a proxy
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[5]
Httpd_accel_port
Httpd_access
80
Deny all
Defines a port number of
real HTTP server
Defines who can access the
Squid server.
The following listing shows the changes to make /etc/squid/squid.conf :
cache_effective_user
squid
cache_effective_group
squid
httpd_acce1_host
squid.example.com
httpd_accel_with_proxy
on
httpd_accel_uses_host_header on
httpd_access
allow
all
Initialize squid\’s cache using squid –z command.
Q.7(d) Explain the two programs used to check the DNS configuration.
[5]
(A)
 The command dig is a tool for querying DNS nameservers for information about host
addresses, mail exchangers, nameservers and related information.
Example : dig mt-example.com
The output tells the technical details about the answer received from DNS server.
Finally it tells the ip address of mt-example.com as
;; ANSWWER SECTION
Mt-example.com
28626 IN A 205.190.150.66
The quick way to get the answer only is : dig mtiexamplke.com +short

host – is a simple utility for performing DNS lookup. It is normally used to convert
names to IP addresses and vice versa.
host [name] [server]
name is a domain name that is to be looked up. It can also be an ip address. In which
case host will by default perform a reverse lookup for the address.
Server is an optional argument which is either the name or IP address of the name
server that host should query instead of the server or servers listed in /etc/resolv.conf
[5]
Q.7(e) Write the purpose of following vsftpd configuration directives :
(i) anonymous_enable
(ii) writeenable
(iii) ftpd_banner
(iv) banned_email_file
(v) chown_username
(A)
(i) anonymous_enable
anonymous_enable=YES, allows anonymous FTP access. You can set this to NO if you do
not want to enable anonymous FTP.
(ii) write_enable
write_enable=YES enables all variations of the FTP commands that allow FTP users to
modify the file system, such as STOR (the FTP put and mput commands for uploading
files) and DELE (the FTP del command for deleting files). As a rule, it is unwise to
permit FTP users to modify the file system, so if security is a concern, you might
consider disabling write commands by setting write_enable to NO.
(iii) ftpd_banner
The ftpd_banner directive allows you to display a site-specific banner message when
users connect to the server. For example, the directive ftpd_ banner=* * * * Welcome
to the Possum Holler FTP Server * * * * looks like the following when users first log in:
220 * * * * Welcome the Possum Holler FTP Server * * * *
Vidyalankar : T.Y. B.Sc. (IT)  Linux
(iv) banned_email_file
If you want to deny access to your server based on the email address providedas part
of an anonymous login, uncomment the deny_email_enable = YES and put the email
addresses you want to deny access into a file named /etc/vsftpd.banned_emails. If you
want to store the banned addresses in a different file, uncomment the
banned_email_file=/etc/vsftpd.banned_ emails directive and change the filename.
(v) chown_username – the user mentioned here is allowed to login via ftp.
chown_username=whoever
Q.7(f) What are the changes in Apache 2?
[5]
(A)
 The build system was rewritten to use the standard GNU build tools, namely, sutoconf
and libtool.
 A new API for modules removes most requirements for loading modules in a certin
order.
 Apache 2 supports IPv6 on those systems that have IPv6.
 Apache’s regular expression support has been replaced using Perl-Compatible Regular
Expression (PCRE).
 HTTP error messages generated by the server can be displayed in multiple languages
using server-side includes (SSI).
 Filters to modify the httpd input or output stream can be implemented as modules,
ionproving the performance of those filters.
 The configuration language has been simplified and rationalised. Confusing directives
such as Port and BindAddress have been replaced by Listen.

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