Hello Tom,
I think I found a workaround. Let me share some new findings:
- What breaks the conversion is not upgrade to 7.6, it is a newer update (to kernel 3.10.0-957.5.1; standard 7.6 installation has kernel 3.10.0-957). It seems it has been rolled out on 01/29 for CentOS, perhaps earlier for RHEL. I.e. after running 'yum update' on a fresh 7.6 installation, that machine can't be converted either.
- The process that hangs during dracut is execution of 'lvm vgs'
- In the setup I use for testing, the root volume is logical and the boot volume is basic. If the conversion is done w/o preserving lvm, i.e. to let the root volume become basic, the conversion succeeds. I suppose logical volumes other than root wouldn't affect dracut but haven't verified that. This means that there is crude workaround - to convert with making root volume basic. This isn't good enough, though.
- It occurs that during the recent '...5.1' kernel update, the lvm binary has been updated as well. By changing /usr/sbin/lvm with one that comes with a fresh 7.6 installation (with kernel 3.10.0-957), the conversion succeeds. That's the workaround I would suggest.
To complicate things, the new lvm build has exactly the same version as the old one, though they differ in size.
Regards,
Plamen