[Yum] Problematic 'yum' repository paths using --installroot option

[Peter Willis]

Hello,

I am attempting to build an exported file system for diskless nodes.

My distribution is Scientific Linux 7.7, which is a Redhat variant, and the command I am using is:

yum install @Base kernel dracut-network nfs-utils --installroot=/node_root --releasever=/

The repository problem manifests as a mistranslation of the  '$slreleasever'   environment variable.
 
This makes all the FTP repositories used by YUM malformed. The value '$slreleasever'  appears to be inserted to the URLs rather than the proper value  '7x'. Hence the URLs read:

http://ftp.scientificlinux.org/linux/scientific/%24slreleasever/x86_64/os/Packages/

rather than:

http://ftp.scientificlinux.org/linux/scientific/7x/x86_64/os/Packages/


Has anyone encountered this issue with yum before?

Is there a solution? 

I have tried       'yum clean all'    and friends.

Thanks for any help