Trying to build a package in mock on a el7 box gives me the following output: INFO: Installed packages: Start: build phase for epson-inkjet-printer-escpr-1.6.13-1.1lsb3.2.fc27.src.rpm Start: build setup for epson-inkjet-printer-escpr-1.6.13-1.1lsb3.2.fc27.src.rpm sh: /usr/bin/cups-config: No such file or directory Building target platforms: x86_64 Building for target x86_64 Wrote: /builddir/build/SRPMS/epson-inkjet-printer-escpr-1.6.13-1.1lsb3.2.fc25.src.rpm No such command: builddep. Please use /usr/bin/dnf --help It could be a DNF plugin command. ERROR: Exception(/home/susi/fedora/epson-inkjet-printer-escpr/master/epson-inkjet-printer-escpr-1.6.13-1.1lsb3.2.fc27.src.rpm) Config(fedora-25-x86_64) 7 minutes 59 seconds INFO: Results and/or logs in: /var/lib/mock/fedora-25-x86_64/result ERROR: builddep command missing. Please install package dnf-plugins-core. After installation of dnf-plugins-core, mock works. dnf-plugins-core should be added to the Requires of mock.
Mock on RHEL does not even require DNF. It is soft dependence. Mock can work without DNF just fine. You can even configure it to use YUM to install fedora-27 chroot. It should be listed as soft dependence, but RHEL{6,7} cannot handle weak dependencies. The other option will force dnf and dnf-plugins-core for all users of mock, which is really unnecessary.