Avec https://www.maketecheasier.com/update-upgrade-ubuntu-without-internet-connection/

apt update && apt dist-upgrade && apt autoremove
apt-get install update-manager-core
# Après vérification du bon channel dans "/etc/update-manager/release-upgrades", valider "lts"
do-release-upgrade -d

Script ''php'' de scan manuel des fichiers, quand on n'a aucun accès console à l'hébergement.

<?php
// copy the script into the nextcloud mainfolder where console.php is located, e.g. /var/www/nextcloud
$path = realpath(dirname(__FILE__));
echo "PHP Version: " . phpversion() ."<br>";
// run upgrade routines after installation of a new release. The release has to be installed before.
//exec("php $path/console.php upgrade 2>&1", $out, $result);
// rescan filesystem
exec("php $path/console.php files:scan --all -v 2>&1", $out, $result);
// for more commands see documentation
echo "Returncode: " .$result ."<br>";
echo "Console output: " ."<br>";
echo "<pre>"; print_r($out);
?>

Avec partie 2 : https://vblog.io/de-vsphere-6-0-a-vsphere-6-5-seconde-partie-raison-et-sentiments/

Suffit de changer les versions pour Stretch. Via https://framapiaf.org/@framasky/1465792