Commands to live-upgrade CentOS Streams 8 -> 9

centos8-9.sh

# The general procedure here is adapted from the 7->8 guide here. https://www.tecmint.com/upgrade-centos-7-to-centos-8/
#
# It is a curated list of my bash history. I entered other commands so hopefully I got the right ones here.

yum upgrade
reboot
dnf install epel-release
dnf install rpmconf
dnf install yum-utils
rpmconf -a  # answer "n" to both things
package-cleanup --leaves
package-cleanup --orphans
dnf install http://mirror.stream.centos.org/9-stream/BaseOS/x86_64/os/Packages/centos-stream-repos-9.0-9.el9.noarch.rpm http://mirror.stream.centos.org/9-stream/BaseOS/x86_64/os/Packages/centos-stream-release-9.0-9.el9.noarch.rpm http://mirror.stream.centos.org/9-stream/BaseOS/x86_64/os/Packages/centos-gpg-keys-9.0-9.el9.noarch.rpm
curl -O https://dl.fedoraproject.org/pub/epel/epel-release-latest-9.noarch.rpm
curl -O https://dl.fedoraproject.org/pub/epel/epel-next-release-latest-9.noarch.rpm
rpm -Uvh *.rpm
yum update
dnf clean all
rpm -e `rpm -q kernel`
dnf -y --releasever=9 --allowerasing --setopt=deltarpm=false distro-sync
dnf clean all
reboot
rm -f /var/lib/rpm/__db*
rpm --rebuilddb
dnf -y groupupdate "Core" "Minimal Install"

What to do about
warning: Signature not supported. Hash algorithm SHA1 not available.

A Google search leads to https://www.redhat.com/en/blog/rhel-security-sha-1-package-signatures-distrusted-rhel-9
but that doesn't solve anything

Nevermind.. after removing the old kernel, despite the new kernel being installed, the system hangs at grub.
Just once I'd like to use something professionals create.

You can remove the modules by deleting their metadata files from /etc/dnf/modules.d/

The simplest method.

why 3 lines instead of one?
dnf install epel-release rpmconf yum-utils

how is this second hit on google? dont do dis guys

In my case this left me without a grub entry pointing to a working kernel so after the reboot grub2 failed to find a working kernel. I was able to boot off a centos iso and rescue the system to get it mounted. Then installed the iso's kernel rpm into the mounted root. Then chroot to the mounted root and performed a grub2-mkconfig. That got me a working kernel and config. Once that was all done the reboot bought me back into a working system where these steps finished cleanly. So maybe before the reboot there should be an attempt to dnf install kernel? then a grub2-mkconfig to ensure grub's configs are updated to target that new kernel.

Thanks, It's not exactly the configuration I used but it was interresting.
If i can i will commit a Fork wen I will finished my configuration :)