All (really all?) the opam conf packages are just interfaces to the respective OS packages,
so you would normally need the package plus the dev-package for it.

Just search with apt-cache, apt-file, or command-not-found (beware the recursion, the latter two have to be installed :-)

/Str.

On 28.03.2016 05:08, Helmut Brandl wrote:
I have severe problems installing some packages with opam. I want to install 'js_of_ocaml' with opam, but it cannot install the package 'conf-pkg-config'. In trying to do this I get the error:
opam install conf-pkg-config
The following actions will be performed:
  ∗  install conf-pkg-config 1.0

=-=- Gathering sources =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

=-=- Processing actions -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
[ERROR] The compilation of conf-pkg-config failed at "pkg-config --help".

#=== ERROR while installing conf-pkg-config.1.0 ===============================#
# opam-version 1.2.2
# os           linux
# command      pkg-config --help
# path         /home/helmut/.opam/4.02.3/build/conf-pkg-config.1.0
# compiler     4.02.3
# exit-code    127
# env-file     /home/helmut/.opam/4.02.3/build/conf-pkg-config.1.0/conf-pkg-config-11348-42bb52.env
# stdout-file  /home/helmut/.opam/4.02.3/build/conf-pkg-config.1.0/conf-pkg-config-11348-42bb52.out
# stderr-file  /home/helmut/.opam/4.02.3/build/conf-pkg-config.1.0/conf-pkg-config-11348-42bb52.err



=-=- Error report -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
The following actions failed
  ∗  install conf-pkg-config 1.0
No changes have been performed

=-=- conf-pkg-config.1.0 troobleshooting =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
=> This package relies on external (system) dependencies that may be missing. `opam depext conf-pkg-config.1.0' may help you find the
   correct installation for your system.

The recommended check does not give any information.

I have installed the version 4.02.3 successfully via opam and switched to that version.

Any ideas on how to analyze the problem?

Regards
Helmut