How To Take The Backup Of MBR(Master Boot Recorder)

1.How to take the backup and restore MBR? Why do you require to take the backup of your MBR?
Ans : MBR (Master Boot Recorder) is a vital part of your hard disk which contains booting information, without it its difficult to boot the system. Suppose you have windows and Linux duel boot on your machine and as you know windows is more prone to virus attacks. So it’s always better to backup your MBR to be in safe place.

2. How to take backup of your MBR?
Ans : Using dd command (dataset definition). Here are the steps to take backup of you MBR and keep it in safe place to restore your system if it get corrupted.
#dd if=/dev/hdx of=/safe/location bs=512 count=1

Let me explain the above command how it will work.
“If” in the command is nothing but to specify Input File, here we are specifying our input file as hard disk(if the hard disk is /dev/hda it is primary master, so for general purpose I given 'x'). “of” in the command is nothing but to specify Output File, here we are specifying our output file as /safe/location. Then “bs” this is nothing but block size to write in to hard disk. And then “count” nothing but how many times you want to write date this many block sizes. Here in this example count=1 that means first 512 bytes of the hard disk is copied to the specified location.

3.How to restore the MBR?
#dd if=/safe/location of=/dev/hdx bs=512 count=1

Note : Please replace “hdx” with your hard disk name.
This is bit complex, Is there any other way to restore MBR?
Yes, if you have Linux or Windows bootable CD, we can easily restore your MBR if you forgot to take backup(And this method is very much easy to do restoration of MBR when compared to previous method).

Method1 : With Redhat Linux bootable CD.
For this you have to boot your system to rescue mode, then mount your file system to rescue mode and execute below command to restore your MBR
#grub-install /dev/hdx

Note : Please replace hdx with your hard disk name. After that you just reboot your system. Your system will be live and working.

Method2 : With Windows XP bootable CD.
Step1 : Boot the system with XP bootable cd
Step2 : Press f8 to go to repair mode in Windows
Step3 : Once you got the c drive prompt just type below command
Fixmbr
This command will fix the MBR record.

Some FAQ’s
1. What is the MBR size?
Ans : MBR size is just 512 bytes.

2.What MBR conations?
Ans : Mainly MBR can be divided in two parts
a.Boot loader information block(which is of 448 bytes)
b. Partition table information(which is of just 64 bytes)

3.How many partition we can create on a hard disk?
Ans : Totally we can create four partitions as below
a.Four primary parathions.
b.Three primary and one extended partition.
c.Two primary and one extended parathion.
d.One primary and one extended parathion.

Note : In extended parathion we can create logical partitions up to 24 in number.

4.Why we cannot create more then 4 partition as mention above?
Ans : In MBR, the partition table info is just stored in 64 bytes, and one parathion information to store in MBR requires 16 bytes of space. So at most you can create only 4 partitions as mention above.

Please Comment your thoughts regarding this post:-)

Like the post? Please Subscribe to free RSS feed to get updates

EXT2 VS EXT3 File Systems

The differences between Ext2 and Ext3 file systems are as follows.

Sl.No	EXT2	EXT3
Journling	No journling	Has journling
Speed of file system(read-write)	Bit faster	Bit slower then ext2 file-system
Data corruption	File system may be corrupted due to unplanned reboots	Prevents file-system corruption
Way to recover data	Require fsck to recover data after unplanned reboot	Does not require(automatic file recovery is done at booting time)
Online file system growth.	By default there is no Online file system growth.	Online file system growth
Commands to format	mkfs.ext2 or mke2fs	mkfs.ext3 or mke2fs -j
Max file size(if block size is 1kB)	2GB	16GB
De-fragmentation	Easy and done with e2defrag	There is no data security when doing de-fragmentation.
Data accommodation	More data can be accommodated in a give space	Less date is written when compare to ext2 in a give space due to journling.

Some FAQ's:

1. What is Journaling?
Ans : In general, Journaling file systems avoid file system corruption by maintaining a journal. The journal is a special file that logs the changes destined for the file system in a circular buffer. At periodic intervals, the journal is comitted to the file system. If a crash occurs, the journal can be used as a checkpoint to recover unsaved information and avoid corrupting of file system metadata.
2.How many file systems supported by linux? and what are they?
Ans : As of now(09-Nov-2009) Linux will supports : Btrfs, cifs, davfs, ext, ext2, ext3, ext4, exofs, hpfs, JFS minix, msdos, ncpfs, NiLFS(2), ntfs, nfs, proc, smbfs, iso9660, sysv, hpfs, affs, ufs, umsdos, vfat, xia, xfs, ZFS.
Note : Please add some more file systems which you people know in the comment section. So that i will update the post with new file systems.

3.What is the maxium size of a paration we can create using ext2 and ext3?
Ans : 4TB paratation can be created in each ext2 and ext3 file system respectively.

4.What is the maxium size of a file we can create in ext2?
Ans : The maximum size what we can create is 2GB to 2TB. It depends on the block size we taken when we are formating. If the block size is 1KB we can not create a file more than 2GB in ext2 file system.

5.What is "ext" in ext2 and ext3?
Ans : When linux first implemented the default file system is minixfs, in subsequent years it was replaced its sucesser file system called extended filesystem. So the naming convention. So ext2 is second version of extended file system. Same explanation is given to ext3 and ext4.

6. Some points about ext4
a.It supports 64 bit storage limits, where as ext, ext2, ext3 are 32Bit storage limits and minix is 16Bit storage limit.
b.Have backward compatibility and performance is improved from lower version.
c.Extents are introduced (An extent is a range of contiguous physical blocks, improving large file performance and reducing fragmentation. A single extent in ext4 can map up to 128MB of contiguous space with a 4KB block size).

And there are many more advantages please see the below links for more info about all the file systems..
http://en.wikipedia.org/wiki/Ext4
http://en.wikipedia.org/wiki/Ext3
http://en.wikipedia.org/wiki/Ext2
http://en.wikipedia.org/wiki/Extended_file_system
http://www.ibm.com/developerworks/library/l-journaling-filesystems/index.html
http://www.oracle.com/technology/pub/articles/calish_filesys.html
http://www.cyberciti.biz/tips/understanding-unixlinux-file-system-part-i.html Please comment your thoughts regarding this post. To give feed back click here.

Like the post? Please Subscribe to free RSS feed to get updates

Linux Virtual File System

Can we create a file system (i.e. formatting a drive/partition) with in a file system?
Looks little bit strange is int it? So follow me I will show you how to create a virtual partition and file system within a partition.

Step1 : Create a empty file with /dev/zero with size equal to 50Mb.
#dd if=/dev/zero of=/temp/vf0 count=102400

Note :
1. By default "dd" command(dataset definition) uses block of 512bytes so the size will be 102400*512=52 428 800=~50MB
2. /dev/zero is a device files which will be used create a file which conations "0" i.e. an empty file.

Clipped output:
[root@test6 ~]# dd if=/dev/zero of=/temp/vf0 count=102400
102400+0 records in
102400+0 records out
[root@test ~]# ls -lh /temp/vf0
-rw-r--r-- 1 root root 50M Nov 7 12:08 /temp/vf0

Step2 : Create ext3 file system for this virtual partition.
#mkfs -t ext3 /temp/vf0

Here it will ask "do you want to format the file or not"?, just say yes.

Step3 : Now we have to create a mount point (nothing but a directory) and mount the created partition.
# mkdir /virtdrive
# mount -o loop=/dev/loop0 /temp/vf0 /virtdrive

Note:
/dev/loop is special hardware device used to mount ISO files and virtual file systems. In Linux there are total 8 loop devices numbering from 0 to 7. So you can mount only 8 ISO files/virtual file systems by default.

Step4 : Edit /etc/fstab file to mount permanently, so that it be auto mounted at boot time too. Specify following entry in fstab file.
/temp/vf0 /virtdrive ext3 rw,loop=/dev/loop0 0 0

Step5 : Specify the fstab changes to kernel.
#mount -a

Step6 : Conform Weather mounting happen perfectly or not.

Way1 :
#cat /etc/mtab

Way2 : Change the directory to mount point you have to see lost+found folder
[root@test ~]# cd /virtdrive/
[root@test virtdrive]# ls
lost+found
[root@test virtdrive]#

Please comment your thoughts regarding this post:-)

Like the post? Please Subscribe to free RSS feed to get updates