[CentOS] Updating microcode_ctl froze Centos7

Fri Jun 12 07:20:34 UTC 2020
Robin Lee <robinlee at mailbox.org>

Today when I ran yum update two packages came up microcode_ctl
and unbound-libs. The updating process went fine until it outputted 

Running transaction
  Updating   : 2:microcode_ctl-2.1-61.6.el7_8.x86_64

then it just froze. I could no longer ssh to the machine and the
console was just blank. I had to shut down it hard. It came back up
seemingly fine. But yum update doesn't work anymore. It says "Error
importing repomd.xml from base/7/x86_64: Damaged repomd.xml file"
I looked at the logs, but journalctl only shows the latest boot on this
machine. 

So I guess I have three questions
- Any idea what happened with the update process?
- How can I repair repomd.xml?
- How do I configure journalctl to store more boots?

/Robin