I have removed mbr by mistake.

Now I can't boot ubuntu, so I want to reinstall grub.

I'm following this instructions.

The problem is that I'm getting this error:

grub-install --boot-directory=/media/cab64688-2d97-4bbd-9f32-7bc0badb40a8/boot /dev/sdb

rm: cannot remove `/media/cab64688-2d97-4bbd-9f32-7bc0badb40a8/boot/grub/915resolution.mod': Read-only file system

So, problem is that my existing ubuntu partition is mounted read only. When I try:

sudo mount /dev/sdb7  /media/ubuntu_mpt

mount: block device /dev/sdb7 is write-protected, mounting read-only

So I failed to install grub since I'm in read only mode.

Any idea?

Thanks in advance.

EDIT: After apt-get install grub, I repeated the process and got:

Probing devices to guess BIOS drives. This may take a long time.

Unknown partition table signature

sed: can't read /media/cab64688-2d97-4bbd-9f32-7bc0badb40a8_/boot/grub/device.map: No such file or directory

grep: /media/cab64688-2d97-4bbd-9f32-7bc0badb40a8_/boot/grub/device.map: No such file or directory

/dev/sda does not have any corresponding BIOS drive.

EDIT: Requested outputs:

fdisk -l



Disk /dev/sda: 163.9 GB, 163927522816 bytes

255 heads, 63 sectors/track, 19929 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x00000000



Disk /dev/sda doesn't contain a valid partition table



Disk /dev/sdb: 640.1 GB, 640133946880 bytes

255 heads, 63 sectors/track, 77825 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x3dcf5202



   Device Boot      Start         End      Blocks   Id  System

/dev/sdb1   *           1        3917    31463271    7  HPFS/NTFS

/dev/sdb2            3918       77826   593667163    f  W95 Ext'd (LBA)

/dev/sdb5            3918       43080   314576766    7  HPFS/NTFS

/dev/sdb6           77328       77826     4000768   82  Linux swap / Solaris

/dev/sdb7           43081       77197   274041856   83  Linux

/dev/sdb8           77197       77327     1045504   82  Linux swap / Solaris



Partition table entries are not in disk order



Disk /dev/sdc: 4043 MB, 4043284480 bytes

125 heads, 62 sectors/track, 1018 cylinders

Units = cylinders of 7750 * 512 = 3968000 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x6f20736b



This doesn't look like a partition table

Probably you selected the wrong device.



   Device Boot      Start         End      Blocks   Id  System

/dev/sdc1   ?      100405      247697   570754815+  72  Unknown

Partition 1 has different physical/logical beginnings (non-Linux?):

     phys=(357, 116, 40) logical=(100404, 79, 11)

Partition 1 has different physical/logical endings:

     phys=(357, 32, 45) logical=(247696, 24, 51)

Partition 1 does not end on cylinder boundary.

/dev/sdc2   ?       21767      271577   968014120   65  Novell Netware 386

Partition 2 has different physical/logical beginnings (non-Linux?):

     phys=(288, 115, 43) logical=(21766, 48, 47)

Partition 2 has different physical/logical endings:

     phys=(367, 114, 50) logical=(271576, 60, 42)

Partition 2 does not end on cylinder boundary.

/dev/sdc3   ?      241276      491086   968014096   79  Unknown

Partition 3 has different physical/logical beginnings (non-Linux?):

     phys=(366, 32, 33) logical=(241275, 3, 30)

Partition 3 has different physical/logical endings:

     phys=(357, 32, 43) logical=(491085, 14, 39)

Partition 3 does not end on cylinder boundary.

/dev/sdc4   ?      372346      372354       27749+   d  Unknown

Partition 4 has different physical/logical beginnings (non-Linux?):

     phys=(372, 97, 50) logical=(372345, 119, 25)

Partition 4 has different physical/logical endings:

     phys=(0, 10, 0) logical=(372353, 14, 33)

Partition 4 does not end on cylinder boundary.



Partition table entries are not in disk order



mount

aufs on / type aufs (rw)

none on /proc type proc (rw,noexec,nosuid,nodev)

none on /sys type sysfs (rw,noexec,nosuid,nodev)

fusectl on /sys/fs/fuse/connections type fusectl (rw)

none on /dev type devtmpfs (rw,mode=0755)

none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)

/dev/sr0 on /cdrom type iso9660 (ro,noatime)

/dev/loop0 on /rofs type squashfs (ro,noatime)

none on /sys/kernel/debug type debugfs (rw)

none on /sys/kernel/security type securityfs (rw)

none on /dev/shm type tmpfs (rw,nosuid,nodev)

tmpfs on /tmp type tmpfs (rw,nosuid,nodev)

none on /var/run type tmpfs (rw,nosuid,mode=0755)

none on /var/lock type tmpfs (rw,noexec,nosuid,nodev)

binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,noexec,nosuid,nodev)

gvfs-fuse-daemon on /home/ubuntu/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=ubuntu)

/dev/sda on /media/Backup type ext4 (rw,nosuid,nodev,uhelper=udisks)

/dev/sdb7 on /media/cab64688-2d97-4bbd-9f32-7bc0badb40a8_ type ext4 (ro,nosuid,nodev,uhelper=udisks)



ls -lA /dev/disk/by-label

total 0

lrwxrwxrwx 1 root root 9 2011-06-12 18:32 Backup -> ../../sda

lrwxrwxrwx 1 root root 9 2011-06-12 18:31 Ubuntux2011.04x20i386 -> ../../sr0