CentOS-7 made my other linux (RH6.10) unbootable

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fermiproxy
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CentOS-7 made my other linux (RH6.10) unbootable

Post by fermiproxy » 2021/10/22 23:03:08

I recently installed CentOS-7 along with Windows and RH-6.10. CentOS installation proceeded just fine. After that, I started running it and getting acquainted with it. My Windows is also fine. But My RH-6.10 is now unbootable.

The CentOS boot selection menu includes RH linux installation (as well as Windows). So it clearly recognizes RH-6.10 as another OS residing on the disk. Unfortunately, when I select it, it fails to boot with the messages: "can't find command 'linux' " and "can't find command 'initrd' ". If I knew what caused this, I probably could fix it in the rescue mode for RH linux. But I have no idea why this happened. Can anyone offer suggestions as to how the CentOS installation might have caused this problem?

Thanks in advance.

PS: Just in case, let me add a possibly redundant statement: Yes, my RH linux installation was perfectly bootable before I installed CentOS an hour ago.

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TrevorH
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Re: CentOS-7 made my other linux (RH6.10) unbootable

Post by TrevorH » 2021/10/22 23:29:13

You can't run both 6 and 7 in a dual boot mode easily. They use totally different versions of grub, one Grub Legacy and the other Grub2 which is now the only supported version around. You would have to chain boot from CentOS 7 with grub2 in the MBR and set the CentOS 6 side up to install grub legacy in the PBR not the MBR. So you'd get the CentOS 7 grub screen with the CentOS 6 option then that would start the CentOS 6 grub.

However, after all that, 6 is dead and has been for nearly a year. If it's a RHEL EUS subscription then you get updates for a while yet but if it's not then it's getting increasingly insecure.
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke

fermiproxy
Posts: 13
Joined: 2021/10/19 02:16:33

Re: CentOS-7 made my other linux (RH6.10) unbootable

Post by fermiproxy » 2021/10/23 01:05:18

Thank you, TrevorH for the reply. However, what you said appears to be well beyond my limited Linux boot configuration knowledge to implement for RH6.10. If there is nothing simple I can do for RH-6.10 in the rescue mode, then I have to throw the towel in, and I have to uninstall CenstOS in the hope that this will make RH6.10 bootable again. I have too much legacy code in there too throw it away.

So, will uninstalling CentOS make RH6.10 bootable again? Or will I have to doctor the files associated with grub anyway to save it?

Thanks for helping.

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TrevorH
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Re: CentOS-7 made my other linux (RH6.10) unbootable

Post by TrevorH » 2021/10/23 04:41:11

will uninstalling CentOS make RH6.10 bootable again?
No. It will not. In fact it will render everything else unbootable too, especially since there is no "uninstall" option.

Boot the RHEL 6.10 install media and when you get the first screen with the option to install/verify&install, hit tab to edit the list of options and remove 'quiet' and 'rhgb' and append 'rescue' (no quotes). That will boot in rescue mode and will ask you if you want to mount your system partitions and drop to a shell. Do so. Now your RHEL 6 system filesystems should be mounted under /mnt/sysimage. Use chroot /mnt/sysimage to chroot into it and now you are sitting at a bash command prompt that looks like your RHEL 6 system.

Unfortunately I have deleted my CentOS 6 VM so I cannot boot it to look around to see how things used to work on it. From that bash prompt you should be able to reinstall grub - most likely using grub-install but read the man page on how to use it. And hope that the CentOS 7 install did not delete the old grub legacy config file in /boot/grub/grub.conf.

Or, more likely the longer term solution, boot CentOS 7 and use that to mount your 6 filesystems and copy the things you need over from there and run them on CentOS 7. 6 is either dead (if it's CentOS or not RHEL+EUS) or if it's EUS then it's dying and I think you have another 2 years before that goes pop too.
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke

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