@Micha: Danke für den Artikel. Das ist das Verständlichste, was ich (als Laie) zu dem Thema bisher gesehen habe.
@Geier0815. Danke für die Ergänzungen. Er meckert über "https://" bei beiden Befehlen.
root@linux:/home/axel# apt-key adv --recv-keys --keyserver https://keyserver.ubuntu.com 0E98404D386FA1D9
Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).
Executing: /tmp/apt-key-gpghome.PUpqdWUyLN/gpg.1.sh --recv-keys --keyserver https://keyserver.ubuntu.com 0E98404D386FA1D9
gpg: Malformed URL; expected hkp: or hkps:
root@linux:/home/axel# gpg --keyserver https://key.opengpg.org --recv-keys 6ED0E7B82643E131
gpg: Malformed URL; expected hkp: or hkps:
Ohne zu wissen, was das ist oder soll, habe ich es auch mal mit hkp: und hkps: probiert - kein Erfolg:
root@linux:/home/axel# apt-key adv --recv-keys --keyserver hkp://keyserver.ubuntu.com 0E98404D386FA1D9
Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).
Executing: /tmp/apt-key-gpghome.FwHwF46UxG/gpg.1.sh --recv-keys --keyserver hkp://keyserver.ubuntu.com 0E98404D386FA1D9
gpg: key 73A4F27B8DD47936: public key "Debian Archive Automatic Signing Key (11/bullseye) <ftpmaster@debian.org>" imported
gpg: Total number processed: 0
gpg: imported: 1
gpg: error: Broken pipe (os error 32)
gpg: error: Error parsing --import-options
gpg: because: Unknown argument "merge-only"
root@linux:/home/axel# apt-key adv --recv-keys --keyserver hkps://keyserver.ubuntu.com 0E98404D386FA1D9
Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).
Executing: /tmp/apt-key-gpghome.yaStCAVa3l/gpg.1.sh --recv-keys --keyserver hkps://keyserver.ubuntu.com 0E98404D386FA1D9
gpg: key 73A4F27B8DD47936: public key "Debian Archive Automatic Signing Key (11/bullseye) <ftpmaster@debian.org>" imported
gpg: Total number processed: 0
gpg: imported: 1
gpg: error: Broken pipe (os error 32)
gpg: error: Error parsing --import-options
gpg: because: Unknown argument "merge-only"
root@linux:/home/axel# gpg --keyserver hkp://key.opengpg.org --recv-keys 6ED0E7B82643E131
gpg: error sending request for url (http://key.opengpg.org:11371/pks/lookup?op=get&options=mr&search=0x6ED0E7B82643E131): operation timed out
root@linux:/home/axel# gpg --keyserver hkps://key.opengpg.org --recv-keys 6ED0E7B82643E131
gpg: unexpected EOF
Stochern im Nebel...