Linux System Administration Practical

Index

Installation of Linux operating system (kali)

Download the Kali Linux iso file.

Create a new virtual machine.

Open Virtual Machine then create a new Machine for install Linux OS

Click on “Installer disc image file(iso):” and then set the Linux iso file path then click on next.

Select Linux in the Guest operating system then select the suitable version then click next

Fill in the virtual machine name then set the right position to install the Linux OS then click next.

Set the disk capacity “recommended size 20 GB” then click “store virtual disk as a single file” then click next.

If you change any hardware property then click on “Customize hardware” otherwise click finish

Your virtual is ready for use.

Linux Installation

Click on “Play virtual machine”.

Linux Installation starting.

Select a language “English”.

Select your location “India”

Configure your keyboard “American English”

Configure the network

Enter the system hostname

Enter the domain name

Setup the user and password

Enter the user’s full name

Enter the username

Enter the user password

Disk partition

Select the “Guided – use enter disk”

Select disk partition – SCSI33(0,0,0) ……….

Select partitioning scheme – “All files in one partition”

Click on “Finish partitioning and write changes to disk”

Write the change to disk? – yes

Disk partitioning complete

Software Selection for according to the user.

Install the GRUB Boot loader

Click on yes

Select devices for boot loader installation

Linux Installation Finish.

Package Installation

okular package – view pdf files

cmatrix – display matrix in a live way

Package Removing

Shutting down

Working with basic commands

Basic Commands

whoami - User Name

who - User name and details

users - List all users

uname - Print machine name or type

uname -r - Print machine version

uname -r -a - Print all machine details.

pwd - Present working directories

ls - List all folders or files in the present working directory

ls -r - Print all details

ls -a - Print all with hidden files

man command_name - Print command details

cd - Change directory

lsblk - List disk partitioning

cal - Calendar

date - Print date full

wget url - Download any webpage in HTML

ps - Print service

top - List all tools and services currently work

kill pid_number - Close any operation or tool

figlet text - Text print in a different style

factor - Number for finding the factors

shutdown time - Shutdown machine on specific time

Directory Commands and Operations

mkdir folder_name - Create folder

touch file_format - Create any type of file

type > file_format - Create any type of file

echo text > file_name - Create a file with data

cat ./to.txt - print file data

touch .hiddenfile_name - Create hidden file

cp ./filename /location - File copy on location to other

mv /filename /location - Move a file from one location to other

mv old_file_name new_file_name - Rename a file
rm file_name - Remove files in the current directory

rmdir directoryname - Remove empty directory

Linux system administration

superuser – superuser is commonly known as root. It is created by default and has user ID & Group ID as 0. It doesn’t have a password by default one can assign it by

# sudo passwd root

Create new user –

Switch user –

Administrative commands –

man - Display information about all commands
kill - Kill a process
wget - Download file from network
env - Display environment variable for currently logged–in user
cat - Display, copy or combine text files
ifconfig - Display configuration
sudo - Run a command as a root user
su - Switch from one to another user
history - Find the all-history command list.

Administrative configuration files

Check user directory

Check password directory

Configuring NICs with Network Device Configuration Utilities (ip and ifconfig)

Using ip command

Using ifconfig command

Install and configure a DNS Server with a domain name of your choice.

Check Requirements

Check hostname system

Check ip server

Update system

Instal DNS Server

Install DNS

Checking status DNS server

If you have UFW firewall, open up access to BIND

Configure DNS Server

Create Forward zone

DNS query will be forwarded to the forwarders when your local DNS server is unable to resolve query.

Uncomment add your DNS

Create a new forward.hg.local file

Create a new reverse.hg.local file

Check Bind Configuration Syntax

Testing DNS Server

Add DNS server Ip address in /etc/resolve.conf file

Add new: nameserver IP DNS Server

Testing on DNS Server

Testing on Windows

Install and configure a DHCP server and client

Update System

Install DHCP Server

The ISC DHCP server package is available in the official package repository of ubuntu. So, you can easily install it using the APT package manager.

Configure DHCP Server

Backup Configure File of ISC DHCP server in the /etc/dhcp/ directory.

Create a new blank configure file dhcpd.conf in /etc/dhcp/ directory

To check the syntax of dhcpd.conf file for errors.

Restart and Enable ISC DHCP to auto-start during boot time

Checking ISC DHCP service, ensure its running.

Install and configure Mail Server

Set a Hostname and Create DNS Records for Domain

First, set a valid FQDN (Fully Qualified Domain Name) hostname for your Ubuntu server using the hostnamectl command as shown.

Next, you need to add MX and A records for your domain in your DNS control panel that guides other MTAs that your mail server mail.yourdomain.com domain is responsible for email delivery.

Installing Apache, MariaDB, and PHP on Ubuntu

In order to create a running mail server using “Roundcube”, we’ll have to install Apache2, MariaDB, and PHP packages first, to do so, run.

Installing Postfix Mail Server on Ubuntu

Postfix is a mail transfer agent (MTA) which is the responsible software for delivering & receiving emails, it’s essential in order to create a complete mail server.

During installation, you will be asked to choose the type of mail configuration, choose “Internet Site”.

Now enter the fully qualified domain name that you want to use for sending and receiving emails.

Once Postfix is installed, it will automatically start and create a new /etc/postfix/main.cf file. You can verify the Postfix version and status of the service using the following commands.

Testing Postfix Mail Server on Ubuntu

Now try to check your mail server is connecting on port 25 using the following command.

The above message indicates that the connection is successfully established. Type quit closing the connection.
You can also use a mail program to send and read emails using the following command.

Installing Dovecot IMAP and POP in Ubuntu

Dovecot is a mail delivery agent (MDA), it delivers the emails from/to the mail server, to install it, run the following command.

Next, restart the Dovecot service using the following command.

Installing Roundcube Webmail in Ubuntu

Roundcube is the webmail server that you’ll be using to manage emails on your server, it has a simple web interface to do the job, it can be customized by installing more modules & themes.

Next, you need to create a new database and user for Roundcube and grant all permission to a new user to write to the database.

Next, import the initial tables to the Roundcube database.

Create an Apache Virtual Host for Roundcube Webmail

Create an apache virtual host for Roundcube webmail.

Add the following configuration to it.

Next, enable this virtual host and reload the apache for the changes.

You can now access the webmail by going to http://yourdomain.com/roundcubemail/installer/

Next, go to the Database settings and add the database details.

After making all the changes, create a config.inc.php file.

After finishing the installation and the final tests please delete the installer folder and make sure that enable_installer option in config.inc.php is disabled.

Now go to the login page and enter the user name and the password of the user.

Creating Mail Users

In order to start using the Roundcube webmail, you’ll have to create a new user, to do so, run.

Replace “myusername” with the user name you want, create a password for the new user by running.

Now go back to the login page and enter the user name and the password of the newly created user.

Install and configure Apache Web server for hosting websites

Install Apache server

Run the following command to install Apache.

Run the following command to start the Apache process.

Verify that the service is running by executing the following command.

Run the following command to restart Apache.

Configure Apache server

The next step is to set up the web server configuration for the domain. The Apache configuration directory is /etc/apache2 and apache2.conf is the main Apache configuration file. Each domain needs its own Virtual Host configuration file.
The configuration files use the .conf extension, and needs to be saved in the /etc/apache2/sites-available/ directory.
Create a file at /etc/apache2/sites-available/yourdomain.com.conf and add the following lines in it.

Create a directory for the website and then create an index.html file for the website.

Add some content to index.html.

Restart Apache service for the above changes to take effect.

Open any browser and enter the website URL.

Test Apache server

The Apache web server can be tested by entering the server IP address into the browser’s address bar:
http://your_server_ip

Securing a simple network with a Linux firewall

Netfilter: - The Netfilter project enables packet filtering, network address [and port] translation (NA[P]T), packet logging, userspace packet queueing, and another packet mangling. The Netfilter hooks are a framework inside the Linux kernel that allows kernel modules to register call-back functions at different locations of the Linux network stack.

iptables: - iptables is a generic firewalling software that allows you to define rulesets. Each rule within an IP table consists of a number of classifiers (iptables matches) and one connected action (iptables target).

Displaying the Status of Your Firewall

Type the following command as root:

Sample outputs:

The above output indicates that the firewall is not active. The following sample shows an active firewall:

Sample outputs:

-L: List rules.
-v: Display detailed information. This option makes the list command show the interface name, the rule options, and the TOS masks. The packet and byte counters are also listed, with the suffix ‘K’, ‘M’ or ‘G’ for 1000, 1,000,000, and 1,000,000,000 multipliers respectively.
-n: Display IP address and port in numeric format. Do not use DNS to resolve names. This will speed up the listing.

To inspect firewall with line numbers, enter:

Sample outputs:

You can use line numbers to delete or insert new rules into the firewall.
To display INPUT or OUTPUT chain rules, enter:

Stop / Start / Restart the Firewall

If you are using CentOS / RHEL / Fedora Linux, enter:

You can use the iptables command itself to stop the firewall and delete all rules:

-F: Deleting (flushing) all the rules.
-X: Delete chain.
-t table_name: Select table (called nat or mangle) and delete/flush rules.
-P: Set the default policy (such as DROP, REJECT, or ACCEPT).

Delete Firewall Rules

To display line number along with other information for existing rules, enter:

You will get the list of IP. Look at the number on the left, then use the number to delete it. For example, delete line number 4, enter:

OR find source IP 202.54.1.1 and delete from the rule:

-D: Delete one or more rules from the selected chain

Insert Firewall Rules

To insert one or more rules in the selected chain as the given rule number use the following syntax. First find outline numbers, enter:

Sample outputs:

To insert rule between 1 and 2, enter:

To view updated rules, enter:

Sample outputs:

Save Firewall Rules

To save firewall rules under CentOS / RHEL / Fedora Linux, enter:

In this example, drop an IP and save firewall rules:

For all other distros use the iptables-save command:

Restore Firewall Rules

To restore firewall rules form a file called /root/my.active.firewall.rules, enter:

To restore firewall rules under CentOS / RHEL / Fedora Linux, enter:

Drop Private Network Address on Public Interface

IP spoofing is nothing but to stop the following IPv4 address ranges for private networks on your public interfaces. Packets with non-routable source addresses should be rejected using the following syntax: