у меня примерно такая же проблема:
$ cd /var/lib/layman/myreponame
$ cat metadata/layout.conf
masters = gentoo
cache-formats = md5-dict pms
thin-manifests = true
manifest-hashes = SHA256 SHA512 WHIRLPOOL
$ repoman full
!!! Repository 'myreponame' is missing masters attribute in '/var/lib/layman/myreponame/metadata/layout.conf'
!!! Set 'masters = gentoo' in this file for future compatibility