From the Desk of Amit Maheshwari

The Booting process is the first process that is executed when you start a Linux system.
This process is executed in the following steps:

1. The processor searches for the Basic Input/Output System (BIOS) program in the
memory and executes it. BIOS is a program that provides the lowest level interface to
the devices, such as the hard disk, monitor, and mouse, of the system.

2. BIOS runs the Power-On Self Test (POST) program, which checks the system
hardware by verifying the hardware configuration information. The program does this
to ensure that all the required hardware devices are present and functioning properly.

3. BIOS checks the system memory for errors and searches for a bootable device. The
bootable device may either be the hard disk or other bootable devices, such as a CD-
ROM or a diskette drive. The sequence in which BIOS searches for the various
devices for the boot record is called the booting sequence
You can specify the booting sequence by editing the booting sequence information in the
BIOS setup program. To enter the BIOS setup program, you need to press the or
key on the first boot up screen. The boot sequence can be specified as CD-
ROM, C, A, where C represents the hard drive and A represents the diskette drive. In the
preceding boot sequence, BIOS will first search the CD-ROM for the boot record, then
search the hard drive and in the end search the diskette. The following list describes the
sequence in which the boot loader is invoked and loaded:

4. BIOS checks the bootable device for the presence of the Master Boot Record (MBR),
which is the first sector of the bootable device. The MBR is 512 bytes in size and
consists of a boot loader and a partition table. The boot loader contains instructions in
the form of machine code for booting the system. The partition table contains
information about the various partitions of the storage devices, such as the size of the
various partitions and the names of the partitions.

5. BIOS locates and invokes the boot loader by passing the control of the system to the
Initial Program Loader (IPL), also called the first stage of the boot loader, which is
present in the MBR.

6. IPL loads the boot loader in the system memory.

The boot loader takes the control of the system from the IPL when it is loaded into the
memory of the system.

GRUB Configuration File

The GRUB configuration file specifies the various commands that are used to set the
global preferences of the system. The global preferences are the parameters that are not
specific to any operating system and are applicable to the entire menu interface of GRUB.
These preferences are followed by the commands specific to each operating system listed
on the menu interface.

The default location of grub.conf in the filesystem is /boot/grub/grub.conf. A sample
grub.conf file of a system having RHEL5 is shown below:

default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Red Hat Enterprise Linux ES (2.6.18-5.EL5)
root (hd0,0)
kernel /vmlinuz-2.6.9-5.EL ro root=LABEL=/ rhgb quiet
initrd /initrd-2.6.18-5.EL5.img

A sample grub.conf file of a system having RHEL5 and Windows XP operating systems
is shown below:

default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Red Hat Enterprise Linux ES (2.6.18-5.EL5)
root (hd0,0)
kernel /vmlinuz-2.6.18-5.EL5 ro root=LABEL=/ rhgb quiet
initrd /initrd-2.6.18-5.EL5.img
title Windows
rootnoverify (hd0,0)
chainloader +1

In the preceding grub.conf file the various configuration directives are:

· default: Specifies default operating system to load
· timeout: Specifies the time interval, in seconds, GRUB waits for user to select an
operating system from GRUB menu
· splashimage: Specifies the absolute path of the image shown by GRUB on screen at bootup
· hiddenmenu: Specifies GRUB to hide the menu until user presses a key
· title: Specifies the OS name shown in GRUB menu
· root: Specifies the partition where grub is installed
· kernel: Specifies the absolute path of the kernel file to load and label of root partition
· initrd: Specifies the absolute path of the initial RAM disk

· rootnoverify: Specifies the root partition to be used by GRUB but does not mount the partition
· chainloader: Specifies GRUB to load the file as a chain loader

Created By Amit Maheshwari

· Primary partitions
· Logical and extended partitions
· Swap partitions

Each type of partition is assigned a numeric code. This code is automatically generated and has a fixed value. For example, the numerical code of the swap partition is 0×82.
Primary Partitions

When a partition is created on a hard disk for the first time, it is called the primary partition. A hard disk can have a maximum of four primary partitions. From the primary partitions present on the hard disk, only one partition can be subdivided into logical partitions. The partition with the logical partitions is called the extended partition. You can subdivide an extended partition into a maximum of 63 subsections.

The MBR stores the information about all the primary partitions, such as the size of the Partitions in terms of sectors, blocks, and cylinders, and the offset from the zeroth cylinder.

Logical and Extended Partitions :
A hard disk can be divided into a maximum of four primary partitions. Therefore, you can only install four operating systems on a computer. If you want to install more than four operating systems, divide the extended partition into logical partitions.

A logical partition is similar to a primary partition. Each logical partition consists of a pointer that contains the address of the next logical partition. All the logical partitions of a hard disk need to be contiguous.

The first sector of an extended partition contains a block of partition descriptor, which contains the information about all the logical partitions. Linux imposes a limit on the number of types of partitions on a hard disk and on the number of logical partitions on the hard disk.

For example, the maximum number of partitions is 63 on an IDE disk and 15 on a SCSI disk.

Swap Partitions :
A process that runs on a system is allocated certain blocks of the RAM, which are known as pages. Linux identifies the pages that a process can access, and stores those pages in the RAM. When the number of processes that run on a computer increases, the kernel releases the space on the RAM. To do this, the kernel writes the inactive pages back to the hard disk. The storage area of the hard disk where the inactive pages are written back is known as the swap space.

You can specify a swap space as a swap partition, swap file, or a combination of a swap partition and a swap file. A swap partition is a separate division of a hard disk used for storing the pages that are written back from the RAM. A swap file is an ordinary file and is used by an operating system to store the inactive pages from the memory

From the Desk of Amit Maheshwari

Then download Linux (Self-Extracting File) it looks like this
jre-6u14-linux-i586.bin (version may be change)

now login as a root

[root@amit]# mkdir /usr/java ### Create java directory under /usr

then mv jre-6u14-linux-i586.bin file to /usr/java/ by following command

[root@amit]# mv jre-6u14-linux-i586.bin /usr/java

Now make it executable by using following command

[root@amit /usr/java]# chmod u+x jre-6u14-linux-i586.bin

now simply execute it :

[root@amit /usr/java]# ./jre-6u14-linux-i586.bin

NOTE : it require some packages to be pre-installed like
compat-libstdc++ , gcc, compat-libstdc++

After successfully installation make it compatible with FIREFOX by using :

[root@amit /usr/java]# ln -s /usr/java/jre1.6.0_14/plugin/i386/ns7/libjavaplugin_oji.so /root/.mozilla/plugins/

Now restart your Firefox web Browser and Enjoy…..

From the Desk of Amit Maheshwari

To backup: # mysqldump -u root -p (database_name) > filename.sql

To restore: # mysql -u root -p (databsae_name ) < filename.sql

From the Desk of Amit Maheshwari

In the following example we wish to protect a directory called pvt in our htdocs directory.
[root@amit ]# cd /usr/local/apache2/htdocs/
[root@amit.htdocs] # mkdir pvt

Step 2. Create a file named .htaccess
Use your favourite editor to create a file called .htaccess . In the below example we will use vim.
[root@amit.htdocs] # vim .htaccess
Add foloowing lines in .htaccess file
AuthUserFile /usr/local/apache2/conf/.htpasswd #### path of .htpasswd file
AuthName “My Private Password Protect Directory” ### title for the username/password input box.
AuthType Basic
Require valid-user amit #### vaild user name

Step 3. Create the .htpasswd file by adding users
[root@amit.htdocs] # htpasswd -c /usr/local/apache2/conf/.htpasswd amit
New password:
Re-type new password:
Adding password for user amit

This creates a file .htpasswd containing the username amit. Then it will be prompted for a password for amit, which will be stored in the .htpasswd file
So, to create a new users and change the password for existing users, switch to the directory that contain .htpasswd, run this commad # htpasswd -c .htpasswd username

Step 4. Set the permissions on your .htaccess and .htpasswd file
Now use chmod command to chage permission of .htaccess & .htpasswd to make it world-readable

[root@amit.htdocs] # chmod 644 /usr/local/apache2/htdocs/pvt/.htaccess
[root@amit.htdocs] # chmod 644 /usr/local/apache2/conf/.htpasswd

Now you done everything !!!!
Now, anytime you attempt to view your password protected directory (pvt ), any file within it, or recursively any subdirectory of it, you will be prompted for a username and password,
From the desk of Amit Maheshwari

All you need to do is add an exclude line to the end of your [main] section in /etc/yum.conf .

Your /etc/yum.conf should look something like this:

[main]

cachedir=/var/cache/yum

keepcache=0

debuglevel=2

logfile=/var/log/yum.log

exactarch=1

obsoletes=1

gpgcheck=1

plugins=1

installonly_limit=3

exclude= hal bash*

This will prevent upgrades of the hal package as well as bash package while using yum update cmd. The list of apps in the exclude should be space sepeated. Shell wildcards ( * ? ) can also be included.

From the desk of Amit Maheshwari

In Linux Freetds Package provide libraries to connect to the MSSQL database, which can be installed with a yum command:

# yum install php-mssql

the above command asks to install MSSQL extension for PHP, but yum will take care of all the dependencies including Freetds.

Once installed you can use a low level tool like tsql which comes with Freetds to check you setup, but before that edit the Freetds config file (/etc/freetds.conf):

[root@amit]# vim /etc/freetds.conf


[MSSQL]
host = 192.168.1.1
port = 1433
tds version = 8.0

above is a simple configuration that I use to connect to SQL2005/2000 databases. The braces contain a name (any name you like) to refer to the connection from Linux, and host is the IP of the MSSQL Server, port is the port MSSQL is listening on and the tds version is the TDS Protocol Version to use when connecting with database. Now regarding the port, MAKE SURE that you are connecting to the correct MSSQL port. OK, Lets check with tsql now:

# tsql -S MSSQL -U user -P pass

that should give u a prompt like “1>”

Now check whether PHP can connect:

# php -r 'echo mssql_connect("MSSQL","user","pass");'


From the desk of Amit Maheshwari

Here is a very easy tip on how to add a welcome message for your SSH users

If you want that when users connect to your SSH server, they see a banner welcome message after connecting. Then you need to turn on the banner configuration of SSHd in its config file and then create a banner file.

Step 1:

Create a banner file that contains text you want people to see when connecting to your SSH server.

Create and open the banner file:

[root@amit]# vim /home/username/banner

put your message inside it

*****************************************************************
*This is a private SSH Server. You are not supposed to be here. *
*Your information has been logged and a report has been emailed *
*to the admin concerning your unauthorized attempts. *
*****************************************************************

Step 2:

Edit /etc/ssh/sshd_config to set a default banner path.

[root@amit]# vi /etc/ssh/sshd_config

then add the following to the config file:

Banner /path/to/banner

Save the file and quit: :wq

Step 3:

Restart the sshd server.

[root@amit] # /etc/init.d/sshd restart

Step 4:

Try SSH to your server and check Welcome banner on login

From the desk of Amit Maheshwari