Hello marto and others following the thread. Sorry, a bit delayed getting back to you wrt your helpful suggestions.

I've tried to check everything on the Gnu/Linux box where I'm working. The urllist is as you told me:

cpan> o conf urllist

    urllist

        0 [file:///var/mirrors/minicpan]

The perms on the minicpan dir look correct (I run cpan as user "somian"):

$ ls -ld . ./*
drwxrwxr-x 3 root staff 4096 Jan 20 14:29 .
drwxrwxr-x 4 root staff 4096 Jan 20 14:55 ./minicpan
ls -ld ./minicpan/*
drwxr-xr-x 3 somian somian 4096 Jan 21 16:20 ./minicpan/authors
drwxr-xr-x 2 somian somian 4096 Jan 26 13:57 ./minicpan/modules
bq.

The real test diagnostic comes when I try cpanminus (cpanm), like this (made a bash function):

cpanm --sudo --verbose --cascade-search \

                            --mirror file:///var/mirrors/minicpan \

                            --mirror https://cpan.metacpan.org/ "$1"

This works perfectly, and so in a sense my problem is solved. I'd still like to know what the problem with cpan is.

EDIT

As marto pointed out, I ought to cite the version:/usr/local/bin/cpan version 1.64.

cpanm is my go to, if you still want to know where the cpan problem is I'd look at issues and changelogs, you have not shared which version exhibits the problem.