Thank you, Magic Banana.
I tried what you said, but still no success. Here is the report:
:~$ apt-key adv --fetch-keys
http://jenkins.trisquel.info/archive/trisquel/trisquel-archive-signkey.gpg
Executing: gpg --ignore-time-conflict --no-options --no-default-keyring
--homedir /tmp/tmp.vRv7Pc62Yx --no-auto-check-trustdb --trust-model always
--keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg
--keyring /etc/apt/trusted.gpg.d/debian-archive-squeeze-automatic.gpg
--keyring /etc/apt/trusted.gpg.d/debian-archive-squeeze-stable.gpg --keyring
/etc/apt/trusted.gpg.d/debian-archive-wheezy-automatic.gpg --keyring
/etc/apt/trusted.gpg.d/debian-archive-wheezy-stable.gpg --keyring
/etc/apt/trusted.gpg.d/ubuntukylin-archive-keyring.gpg --fetch-keys
http://jenkins.trisquel.info/archive/trisquel/trisquel-archive-signkey.gpg
gpg: key 8D8AEBF1: "Trisquel GNU/Linux (Trisquel GNU/Linux signing key) " not
changed
gpg: Total number processed: 1
gpg: unchanged: 1
I also tried with another web, but I am not either able to go ahead:
:~$ apt-key adv --fetch-keys
https://mirror.fsf.org/trisquel/trisquel-archive-signkey.gpg
Executing: gpg --ignore-time-conflict --no-options --no-default-keyring
--homedir /tmp/tmp.ExYSEHxD9E --no-auto-check-trustdb --trust-model always
--keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg
--keyring /etc/apt/trusted.gpg.d/debian-archive-squeeze-automatic.gpg
--keyring /etc/apt/trusted.gpg.d/debian-archive-squeeze-stable.gpg --keyring
/etc/apt/trusted.gpg.d/debian-archive-wheezy-automatic.gpg --keyring
/etc/apt/trusted.gpg.d/debian-archive-wheezy-stable.gpg --keyring
/etc/apt/trusted.gpg.d/ubuntukylin-archive-keyring.gpg --fetch-keys
https://mirror.fsf.org/trisquel/trisquel-archive-signkey.gpg
gpgkeys: protocol `https' not supported
gpg: no handler for keyserver scheme `https'
gpg: WARNING: unable to fetch URI
https://mirror.fsf.org/trisquel/trisquel-archive-signkey.gpg: keyserver error
I have also tried to add the key manually in Systems Settings > Passwords and
Keys but also nothing happens. When I try later to update the system, I get
the same warnings as I reported in the previous post. Sorry for speaking
previously about error instead of warnings. I am still not familiar with the
correct way of speaking about so many technical aspects... I thanks of all
you for helping me to learn little by little :)
