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I have been using Ubuntu since 9.10. Now Maverick crashed and my MBR is wrecked. I have run dd if=/dev/zero of=/dev/sdb bs=512 count=1 on advice from another Ubuntu user but now I can only install any Windows release and no Ubuntu. How do I completely erase the MBR and then use an Ubuntu live CD or another HDD with Ubuntu on to install a Linux-only MBR please.

I am rather new at the technical side of Linux and have bandwidth shortage problems so I can't download large amounts of data. Thanks in advance!

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dd if=/dev/zero of=/dev/sdb bs=512 count=1 It just fill the MBR with zeroes (on /dev/sdb in this case ...). To install/reinstall MBR you should use grub-install. – LGB Feb 12 '11 at 10:41

I have to admit I don't know exactly what you are asking, but if you want to reinstall the bootloader grub then you need to enter the following at a terminal (Applications->Accessories->Terminal):

sudo grub-install /dev/sda

This will install grub onto your [first] hard drive. You may also want to reload the list of operating systems that grub uses when you startup:

sudo update-grub

Both of these commands will prompt you for your password.

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Follow this detailed guide to reinstall GRUB 2: GRUB 2

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If you prefer a GUI way then download Grub Customizer Portable then mark the applications ‘executable’ after download - Right click > Properties > Permissions > Check ‘allow executing as a programme’ then double-click and run and then click File -> install to MBR. enter image description here

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