[CentOS] Fixing grub/shim issue Centos 7

Thu Aug 6 14:25:30 UTC 2020
Simon Matter <simon.matter at invoca.ch>

> Le 04/08/2020 à 08:31, lpeci a écrit :
>> I had the same problem with my UEFI bios machine and I fixed it so for
>> Centos 7:
>> 1) Boot from an rescue linux usb
>> 2) When the rescue system is running:
>>     2.1) #chroot /mnt/sysimage
>> 3) Config network:
>>     3.1) # ip addr add X.X.X.X/X dev X
>>     3.2) # ip route add default via X.X.X.X    <--- default router
>> 4) And finally:
>>     #yum downgrade shim\* grub2\* mokutil
>>     #exit
>>     #reboot
>> I hope you can fix it with these steps.
> Thanks for the detailed suggestion.
> Unfortunately I couldn't recover the installation, and I had to redo
> everything
> from scratch, which cost me the first two days of my holidays.

Now you know how the Window$ admins suffered all the years :-)

> One thought regularly kept crossing my mind:
> "How on earth could this have passed Q & A ?"

Quite simple I guess. It's one of the cases where you can not test so
easily like other updates. Here you have to make tests on real hardware,
different hardware of all kind and can not do it in the Cloud, a VM or

The only real solution I can think of to prevent this would be to make
preview versions of updates available to the public so that a lot of
people can test them on their hardware, hopefully spare hardware, and give

I think current business models do not support such a way these days.

However one can find strategies to survive. What I do is:

* Never update any system directly from what is provided online. Sync to
local repositories first to control what is fed to your systems.

* Never blindly apply updates. Always do tests on not so important systems
or dedicated test systems first.

* If all goes well, update important systems. If you have multiple
systems, update only one first as another test. Then update others.

I have learned my lessons in the past decades but this was a good wake up
call to follow above rules even more strictly. Better safe than sorry.