if you do not install grub on the master boot record of the hard disk,how can you boot linux?

See the LQ rules re homework.

You previous was answered, but you need to investigate these things yourself to learn.

You can boot from a FlashDrive, a LiveCD or even a floppy.

That being said, if you are more specific on your question, the answers you get will be more informative.

You can create a grub boot cd as described in the link below. You would then have to set the CD drive to first boot priority. The link below is for Grub Legacy. You don't indicate which Linux you have?

http://www.gnu.org/software/grub/man...ble-CD_002dROM

I don't know why you would want to do that. More information on your system and what operating systems/drives/partitions would be helpful.

The Master Boot Record area is at the very beginning of the disk, so is not inside any partition. If you have only one disk and one operating system, it is best to boot from the MBR. But some people want to run more than one OS - like Windows and Linux - on a single disk. I did this for many years. You can either use Grub to boot into both Linux and Windows, or use a Windows utility to boot both Linux and Windows. There are a few advantages to using a Windows boot utility, and if you do, you must install the Grub boot loader within a Linux partition, instead of in the MBR area.

There are more OSes than Linux and Windows, too, and it is possible to run them on the same computer side by side. It is also possible to have numerous disks in the same computer. Unfortunately, you should not have more than one partition of one disk 'active'. Otherwise it might get terribly confusing. So if you are hypothetically running four operating systems on four different disks in the same computer, you will have to install the boot loader for three of them inside a partition, not on the MBR.

Of course, you can also boot from a jump drive, or a network card , too. The possibilities are very numerous. It's hard to think up more scenarios, but they do exist.