Shared folders which are automatically mounted via Shared Folders configuration get the following permissions per default:
root:vboxsf with permission 0770
Per default, nobody is in the vboxsf group, you have to manually add one. Here come’s the oddity. In
/etc/nsswitch.conf
the following line is present:
group: files altfiles systemd
which means, the system looks for groups at first in /etc/group, then in /usr/lib/group and at last in the corresponding systemd module. The group vboxsf is defined in /usr/lib/group which is located in a read-only location, so the usual tools like adduser fail to add the user to the group:
sudo adduser egon vboxsf
results in:
Adding user `egon' to group `vboxsf' ...
gpasswd: group 'vboxsf' does not exist in /etc/group
adduser: `/bin/gpasswd -a egon vboxsf' returned error code 3. Exiting.
To work around the issue, you have to insert the corresponding line from /usr/lib/group into /etc/group:
vboxsf:*:127:
Then the usual commands for adding the user to the group work again.