$ git clone -n https://src.fedoraproject.org/rpms/R-sessioninfo.git /var/lib/mock/f42-build-side-110318-58926523-6569309/root/chroot_tmpdir/scmroot/R-sessioninfo
Cloning into '/var/lib/mock/f42-build-side-110318-58926523-6569309/root/chroot_tmpdir/scmroot/R-sessioninfo'...
$ git fetch origin 31caa3c4e8c142523e5021ca9f24657d5acb677d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-sessioninfo
 * [new ref]         31caa3c4e8c142523e5021ca9f24657d5acb677d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 31caa3c R-maint-sig mass rebuild