On a completely fresh ubuntu 18.04 VM I tried to install opam:
$ wget https://github.com/ocaml/opam/releases/download/2.1.0/opam-2.1.0-x86_64-linux
$ mv opam-2.1.0-x86_64-linux opam
$ chmod 777 opam
$ ./opam init
And here is the error I got
<><> Fetching repository information ><><><><><><><><><><><><><><><><><><><><><>
[ERROR] Could not update repository "default": OpamDownload.Download_fail(_,
"Download command failed: \"/usr/bin/wget --content-disposition -t 3 -O
/tmp/opam-5936-f23d09/index.tar.gz.part -U opam/2.1.0 --
https://opam.ocaml.org/index.tar.gz\" exited with code 5 \"ERROR:
cannot verify opam.ocaml.org's certificate, issued by
\226\128\152CN=Zscaler Intermediate Root CA (zscaler.net) (t)\\\\
,OU=Zscaler Inc.,O=Zscaler Inc.,ST=California,C=US\226\128\153:\"")
[ERROR] Initial download of repository failed.
How should I solve this?