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I already had RHEL 7 on my HDD(I have only one) and now recently installed Ubuntu 14.04. I am unable to create Grub2 entry so that I can use both OS, currently I can only use Ubuntu.

The result for #fdisk -l is :

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00098227

 Device    Boot   Start       End         Blocks    Id  System
/dev/sda1   *   314574848   524290046   104857599+  83  Linux
/dev/sda2       524292094   976771071   226239489    f  W95 Ext'd (LBA)
/dev/sda5       524292096   874369023   175038464    7  HPFS/NTFS/exFAT
/dev/sda6       875397120   976771071    50686976   8e  Linux LVM 

Disk /dev/mapper/rhel-swap: 4043 MB, 4043309056 bytes
255 heads, 63 sectors/track, 491 cylinders, total 7897088 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/mapper/rhel-swap doesn't contain a valid partition table

Disk /dev/mapper/rhel-root: 47.9 GB, 47857008640 bytes
255 heads, 63 sectors/track, 5818 cylinders, total 93470720 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/mapper/rhel-root doesn't contain a valid partition table

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  • Did your run sudo update-grub? – Ron Dec 10 '15 at 15:39
  • That's it. It will check what OSes are installed. – Tung Tran Dec 10 '15 at 15:39
  • Ya I did that. The result is ........... Found initrd image: /boot/initrd.img-3.16.0-53-generic Found linux image: /boot/vmlinuz-3.16.0-51-generic Found initrd image: /boot/initrd.img-3.16.0-51-generic Found linux image: /boot/vmlinuz-3.16.0-30-generic Found initrd image: /boot/initrd.img-3.16.0-30-generic Found memtest86+ image: /boot/memtest86+.elf Found memtest86+ image: /boot/memtest86+.bin Found FreeDOS on /dev/sdb1 Found Red Hat Enterprise Linux Server release 7.0 (Maipo) on /dev/mapper/rhel-root done – nabinGhimire Dec 10 '15 at 15:46
  • Make sure fast boot ans secure boot is disabled in bios- update your grub 'sudo update-grub" – DnrDevil Dec 10 '15 at 15:46
  • @DnrDevil I check my bios, there were not such options like fast bootand secure boot . I did sudo update-grub2 and the result says Found Red Hat Enterprise Linux Server release 7.0 (Maipo) on /dev/mapper/rhel-root. – nabinGhimire Dec 10 '15 at 16:07
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Normally Red Hat and related distributions use an LVM configuration in which there's an LVM partition (which you've got) with at least a couple of logical volumes (which you've got) and a separate /boot partition (which you don't seem to have). Without the /boot partition, you won't be able to boot RHEL, since your system won't have a kernel, which is absolutely essential for booting. My suspicion is that you accidentally deleted your RHEL /boot partition when you installed Ubuntu, which I suspect exists on your /dev/sda1. I can't be 100% positive of this diagnosis, though.

There is one small glimmer of hope: Your /dev/sda1 starts at sector 314,574,848, which means there's about 150 GiB of unallocated space at the start of the disk. If /boot was originally in that space, then it may be possible to recover it with TestDisk. You may want to look into that possibility:

A caveat: If I'm right, changing your disk's partition layout runs the risk of creating new problems or making your current problem worse. Doing a low-level backup of the entire disk is a wise precaution. You'd do that with something like:

sudo dd if=/dev/sda of=/path/to/lots/of/space/sda-backup/img

This command is likely to take several hours to complete. You'll need another disk that's at least a little bit larger than your current /dev/sda, mounted somewhere so that /path/to/lots/of/space will reside on that larger disk.

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  • Thank you @RodSmith for the information. I tried TestDisk and was lost, thanks god only the grub entry was erased. I just reinstall grub in /dev/sda and able to use Ubuntu. Will you please mail me or give more info to recover /boot. I am in real need. – nabinGhimire Dec 12 '15 at 10:32
  • There's lots of TestDisk documentation on the Web. You might start with this official TestDisk tutorial or this AskUbuntu question and answer. – Rod Smith Dec 12 '15 at 14:02

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