Alors j'ai d'abord tenté d'ajouter les
guest additions via la VM de VirtualBox en suivant
ceci (c'est comme ça que j'avais fait sur mon ancien PC je crois). Le téléchargement s'est bien passé mais je n'ai pas eu de terminal qui s'est ouvert pour "lancer l'installation". Du coup, j'ai installé les paquets 'virtualbox-ext-pack' et 'virtualbox-guest-addition-iso' (note : il y a un 's' à 'additions') depuis focal-proposed.
toto:~$ sudo apt install virtualbox-ext-pack
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
virtualbox-ext-pack
0 upgraded, 1 newly installed, 0 to remove and 52 not upgraded.
Need to get 10.5 kB of archives.
After this operation, 142 kB of additional disk space will be used.
Get:1 http://fr.archive.ubuntu.com/ubuntu focal-proposed/multiverse amd64 virtualbox-ext-pack all 6.1.16-1~ubuntu1.20.04.1 [10.5 kB]
Fetched 10.5 kB in 0s (57.6 kB/s)
Preconfiguring packages ...
Selecting previously unselected package virtualbox-ext-pack.
(Reading database ... 234481 files and directories currently installed.)
Preparing to unpack .../virtualbox-ext-pack_6.1.16-1~ubuntu1.20.04.1_all.deb ...
License has already been accepted.
Unpacking virtualbox-ext-pack (6.1.16-1~ubuntu1.20.04.1) ...
Setting up virtualbox-ext-pack (6.1.16-1~ubuntu1.20.04.1) ...
virtualbox-ext-pack: downloading: http://download.virtualbox.org/virtualbox/6.1.16/Oracle_VM_VirtualBox_Extension_Pack-6.1.16.vbox-extpack
The file will be downloaded into /usr/share/virtualbox-ext-pack
License accepted.
0%...10%...20%...30%...40%...50%...60%...70%...80%...90%...100%
Successfully installed "Oracle VM VirtualBox Extension Pack".
toto:~$ sudo apt install virtualbox-guest-addition-iso
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package virtualbox-guest-addition-iso
toto:~$ sudo apt install virtualbox-guest-additions-iso
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
virtualbox-guest-additions-iso
0 upgraded, 1 newly installed, 0 to remove and 52 not upgraded.
Need to get 44.7 MB of archives.
After this operation, 61.0 MB of additional disk space will be used.
Get:1 http://fr.archive.ubuntu.com/ubuntu focal-proposed/multiverse amd64 virtualbox-guest-additions-iso all 6.1.16-1~ubuntu1.20.04.1 [44.7 MB]
Fetched 44.7 MB in 10s (4,334 kB/s)
Selecting previously unselected package virtualbox-guest-additions-iso.
(Reading database ... 234486 files and directories currently installed.)
Preparing to unpack .../virtualbox-guest-additions-iso_6.1.16-1~ubuntu1.20.04.1_all.deb ...
Unpacking virtualbox-guest-additions-iso (6.1.16-1~ubuntu1.20.04.1) ...
Setting up virtualbox-guest-additions-iso (6.1.16-1~ubuntu1.20.04.1) ...
toto:~$
Mais je n'ai pas l'impression que l'ISO se soit "installé". J'ai bien un fichier 'VBoxGuestAdditions_6.1.16.iso' sous "/home/toto/.config/VirtualBox/" (je crois que c'est celui qui s'est téléchargé depuis la VM) et dans les paramètres de ma VM j'ai ça :
https://ibb.co/KF5H85v. En fait, je ne comprends pas vraiment en quoi consiste vraiment "l'installation" des
guest additions.
EDIT : je pense que l'installation du paquet 'virtualbox-ext-pack' a créé le dossier "/usr/share/virtualbox-ext-pack/" et l'installation du paquet 'virtualbox-guest-addition-iso' a créé "/usr/share/virtualbox/" contenant 'VBoxGuestAdditions.iso'.