Hello all-- These instructions are somewhat OK but my messed up box is the only one I've got basically to help with this problem. Where can we find "correction" instructions using a "rescue" CD or flash drive? I understand RedHat provided detailed instructions to supported customers. Thanks. _______________________ Sent from MzK's phone. ---------- Forwarded message --------- From: Alan McRae via CentOS <centos at centos.org> Date: Sat, Aug 1, 2020, 19:22 Subject: [CentOS] 8.2.2004 Quick recovery and fix for unbootable machines To: CentOS mailing list <centos at centos.org> This is a quick recovery and fix for the machines rendered unbootable after the grub2/shim yum update. It is written for CentOS 8.2.2004 but similar should work for any CentOS 8 or 7 as long as you get the correct shim file, that is, the one from the latest installation media. I am running on an x86_64 architecture (see uname -i). Please use the correct shim file for your architecture (shim-<arch>-15-11.el8.<arch>.rpm) I have tested this by breaking a machine and then recovering it. It works for me. I hope someone finds it useful. Let me know. Regards Alan HOW TO BOOT AN UNBOOTABLE MACHINE ================================= 1) Download a copy of rEFind. This is a UEFI boot manager. Burn it to a USB key. # wget -O refind.zip http://sourceforge.net/projects/refind/files/0.12.0/refind-flashdrive-0.12.0.zip/download # unzip refind.zip # cd refind-flashdrive-0.12.0 # dd if=refind-flashdrive-0.12.0.img bs=4096 of=/dev/sdX (sdX is the device for your USB key, this will be erased, use the whole device use sdX not sdX1) 1800+0 records in 1800+0 records out 7372800 bytes (7.4 MB, 7.0 MiB) copied, 0.980893 s, 7.5 MB/s 2) Turn off secureboot in your UEFI hardware. 3) Boot the USB key. You should get a colourful screen with icons and a filename below. Use the left/right arrow keys to select the correct grubx64.efi. Hit space to boot. Your usual grub menu should appear and the system should boot normally. HOW TO FIX THE PROBLEM ===================== 1) We need to downgrade the shim package. Now your system is running get an older copy of the correct shim package for your architecture from the CentOS installation media (e.g. CentOS-8.2.2004-x86_64-dvd1.iso) and install it. # mount CentOS-8.2.2004-x86_64-dvd1.iso /mnt # cd /mnt/BaseOS/Packages # cp shim-x64-15-11.el8.x86_64.rpm /root # cd /root # umount /mnt OR Get the package from a CentOS mirror: # cd /root # wget http://ucmirror.canterbury.ac.nz/linux/CentOS/8.2.2004/BaseOS/x86_64/os/Packages/shim-x64-15-11.el8.x86_64.rpm 2) We can now reinstall the older shim package using yum. This will downgrade the package to the working version. # yum install shim-x64-15-11.el8.x86_64.rpm Last metadata expiration check: 2:11:11 ago on Sun 02 Aug 2020 11:31:06 NZST. Dependencies resolved. =========================================================================================== ========================================================================================= Package Architecture Version Repository Size =========================================================================================== ========================================================================================= Downgrading: shim-x64 x86_64 15-11.el8 @commandline 647 k Transaction Summary =========================================================================================== ========================================================================================= Downgrade 1 Package Total size: 647 k Is this ok [y/N]: y Downloading Packages: Running transaction check Transaction check succeeded. Running transaction test Transaction test succeeded. Running transaction Preparing : 1/1 Downgrading : shim-x64-15-11.el8.x86_64 1/2 Cleanup : shim-x64-15-13.el8.x86_64 2/2 Verifying : shim-x64-15-11.el8.x86_64 1/2 Verifying : shim-x64-15-13.el8.x86_64 2/2 Installed products updated. Downgraded: shim-x64-15-11.el8.x86_64 Complete! 3) Your system should now boot normally. 4) add "exclude=shim*" to /etc/yum.conf to prevent the broken one being reinstalled. You should now be able to run 'yum update'. Remove the exclude= when a proper fix becomes available. _______________________________________________ Dear List, I have had 6 of these problems and am on my way to the office to fix two more. Here is what I did with an installation disc along with the advise from the posts of Johny Hughes. So far this has been easy to do and has worked every time. Make sure your system is connected to the network, and know your gateway address and a reasonable ip address of the machine for your network. #1. Boot to tine Install Disc and pick "Recovery Mode" #2. You will be given several options of recover Pick #1 to Continue #3. Use the 'chroot /mnt/sysimage' command to get into your system #4. Activate your network Find the device name you are going to use ip link gives you the name as in 'enp3s0' as the device ip link set dev enpo3s0 up activates the network card ip address add 10.0.0.67/24 dev enp3s0 sets the card's address to 10.0.0.67 with a subnet mask of 255.255.255.0 ip route add default via 10.0.0.124 sets the gateway for your machine to 10.0.0.124 #5. Make sure you have an active domain name service cd /etc/ vim resolv.conf Edit the appropriate value of nameserver 10.0.0.124 (in my case the nameserver and gateway were the same machine) #6. Use of Yum yum clean all This necessary so that you can make sure you have the latest listings yum install shim For Centos 7 you want shim-x64-15-8.el7.x86_64 which Johnny Hughes just released today. When this is installed you will also install mokutil-15-8.el7.x86_64 #7. Exit out of recovery mode, and reboot. This has worked for me every time. Thanks to everyone's advice on this list and all the good work done by the Centos Team!!!! Greg Ennis