Answer / mohammed sajjad

Scenario 1: Backup the boot sector (or MBR)
If the first harddisk in the system is /dev/sda, to backup the boot sector the following command can be used:

# dd if=/dev/sda of=bsbackup.bin bs=512 count=1

Essentially this command will read the first 512 bytes of /dev/sda and write it to the file bsbackup.bin.
Scenario 2: Restore the boot sector from a file:

# dd if=bsbackup.bin of=/dev/sda bs=512 count=1

This will restore the boot sector to /dev/sda that was backed up in Scenario 1.
Scenario 3: Zero out the boot sector (leaving the partition table intact)
Sometimes a virus or other issue can leave a corrupted executable code section in the MBR. I have personally seen a boot sector that would not store grub information (and thus boot linux after its installed) properly until the first 446 bytes were zeroed out and grub re-installed. The following command will do just that:

# dd if=/dev/zero of=/dev/sda bs=446 count=1

Scenario 4: Zero out the entire MBR (this will erase the partition table as well – effectively destroying the ability to easily access data on the drive)
A variation of the last dd command will wipe out the master boot record entirely. You will have to repartition and reformat your hard disk after this:

howmany layers in the OSI model.

1 Answers  

---

Which application protocol can not be blocked by the Switch?

0 Answers   HCL, Samruddhi,

---

what is mean by domain

5 Answers  

---

True or False: The Transport layer deals with packets while the Data Link layer deals with frames.

1 Answers  

---

On a connectionless protocol , how does error recovery and flow control get taken care of ? a. A different protocol has to run along side b. error recovery and flow control are not taken care of c. the upper layers take care of them d. lower layers take care of them

1 Answers  

---

why we r going to freezing service group and system, what are the freezing steps & how to freezing service group?

0 Answers  

---

How can run the computer without Hard disk?

32 Answers   BSRB,

---

any one explain about frame and MAC address,packet and IP address,and segment and port address

2 Answers   IBM,

---

What is called a set of physically connected computers in relatively small physical area.

1 Answers  

---

In the nsswitch.conf file what does the following entry mean ? NOTFOUND=continue

1 Answers  

---

TCP/IP has howmany layers? a. 2 b. 3 c. 4 d. 5

1 Answers  

---

How does the MAC sublayer assure that nothing was damaged in transit? a. CRC b. it can't c. ackwoledgement

1 Answers  

---