build-iso is broken if you have done a repo sync in the last 24 hours. https://bugs.launchpad.net/starlingx/+bug/1901920 A fix has been posted for review https://review.opendev.org/#/c/760175/ If you need to build an iso prior to merge of the fix. A workaround would be to ... cd $MY_REPO/centos-repo/rt/Binary/ createrepo -d . Scott