Oct 23, 2008

How your Linux Boots ?

This is the Normal boot process of a Linux Operating System in to your computer. Boot process takes place in 4 scenes with 4 main characters.

Scene 1
when the computer is switched on,it automatically invokes BIOS[a ROM chip embedded in the motherboard].The BIOS will start the processor and perform a POST[power on self test] to check whether the connected device are ready to use and are working properly. Once the POST is completes BIOS will jump to a specified location in the RAM and check for the booting device.The boot sector is always the first sector of the hard disk and BIOS will load the MBR into the memory.

Scene 2
Here the boot loader takes the control of the booting process.LILO or GRUB are the boot loaders commonly available. It will help the user to select various boot options.Depending on the boot option selected the kernel is loaded.

scene 3

After kernel is loaded the kernel will take the control of the booting process and it will initialize all the hardwares including I/O processors etc.kernel then creates a root device and mounts the partitions.

Scene 4
INIT is loaded

Oct 15, 2008

Encrypt the Mail Attachment.

Now a days internet is considered to be the most unsecured area of data transfer. Most people will send emails with attachment of their confidential matters,agreements etc. Anybody can read once you hack the email. But if attach with an encrypted key,you can open only with the help of a password,which you give at the time of encryption. I am briefing,how to encrypt a file.


OS: Ubuntu 8.04
Application : gpgv

#gpg -c

This time it will ask for the password twice,give it. And you are done. Now you can
see a filename called Filename.gpg. You can send it through internet comfortably.

For Decrypting do the following

#gpg Filename.gpg

Again it will ask for the password. Give ,OK file is decrypted.

Oct 10, 2008

Restart APACHE Safely

In all the Unix like machines ,there is an INIT script running for APACHE. Normally it is located in /etc/init.d/httpd (In case of REDHAT based systems). But in Debian based systems it could be /etc/init.d/apache2. For restarting we use the following

#/etc/init.d/httpd restart (Redhat Based Systems)


#/etc/init.d/apache2 restart (Debian Based Systems)

While doing this command,it will KILL all the listening processes in the machine and stopping and starting Apache. But the problem is while applying the command CLIENTS will losts its all the established connections and result may be an error.

There is a wonderful command is in Apache for preventing this,the command is APACHECTL. Normally called Apache Control. Before restarting apache think once and apply the following

#apachectl -k graceful

The impact is Apache will serve all the established requests to the server. Then only it go for RE-start. User wont have a feelings of this COLD restart.

What is GLUE Record

A glue record is an A record that is created as part of a delegation. If a zone is delegated to a name server whose hostname is a Descendant of that particular zone, then a glue record for that hostname must be included in the delegation.