In https://coq.inria.fr/opam-using.html, under Using OPAM to install Coq, there should be instructions to check what version of OPAM you have (opam --version) before the 2 boxes. Also it probably should say that OPAM 2 is preferred (e.g., it's required to install the version of Dune we'll be using) and point you to the upgrade directions.
I had installed Ubuntu 18.04 and ran apt install opam, which gives you the old version. Since I'm familiar with OPAM upgrade, I thought to check the version. Others may not know to do this.
In https://coq.inria.fr/opam-using.html, under
Using OPAM to install Coq, there should be instructions to check what version of OPAM you have (opam --version) before the 2 boxes. Also it probably should say that OPAM 2 is preferred (e.g., it's required to install the version of Dune we'll be using) and point you to the upgrade directions.I had installed Ubuntu 18.04 and ran
apt install opam, which gives you the old version. Since I'm familiar with OPAM upgrade, I thought to check the version. Others may not know to do this.I followed the instructions at https://opam.ocaml.org/doc/Install.html#Ubuntu to do the OPAM upgrade.