{ os } are invalid field names in /home/vagrant/.opam/opam/core.109.07.00.opam. Valid fields are { opam-version, maintainer, substs, build, remove, depends, depopts, conflicts, libraries, syntax, ocaml-version, build-env, patches, files, license, authors, homepage, version, name, configure-style }
foo!
  'opam update' failed

Fatal error: exception Not_found