[CentOS] strange email from cron regarding "rear"

Wed Oct 7 14:11:32 UTC 2020
Fred <fred.fredex at gmail.com>

I don't understand what this means, I found it in root's email this morning:

To log into the recovery system via ssh set up /root/.ssh/authorized_keys
WARNING: /usr/lib/grub/x86_64-efi/moddep.lst not found, grub2-mkimage will
likely fail. Please install the grub2-efi-x64-modules package to fix this.
ERROR: Error occurred during grub2-mkimage of BOOTX64.efi
Aborting due to an error, check /var/log/rear/rear-fcshome.log for details
/bin/sh: line 1: 30339 Terminated              /usr/sbin/rear mkrescue

It is possible it has happened before, as until recently I haven't paid a
lot of attention to root's email (I know, I know,... bad me).

but I wonder what it's all about... I have not knowingly ever used "rear"
or "mkrescue".

BTW, this is on an up to date Centos-7 X86-64 machine.

Thanks in advance!