xcat/ubuntu - Signature issue

[dmestivier]

dear all,

I try to install xcat on an ubuntu 18.04 under Virtualbox.

I follow the tutorial : https://xcat-docs.readthedocs.io/en/stable/guides/install-guides/apt/index.html
The "Prepare the Management Node" step seems ok.

However, during the "Installing xCAT", things goes wrong.

Whatever the installation mode (automatic or manual, root account),
I add the following message :

root@xcatmn:~# apt-get update
Get:1 file:/root/xcat-core bionic InRelease [2,582 B]
Get:1 file:/root/xcat-core bionic InRelease [2,582 B]
Err:1 file:/root/xcat-core bionic InRelease                                      
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F6F63590468E54F8
Hit:2 http://archive.ubuntu.com/ubuntu bionic InRelease                        
Hit:3 http://archive.ubuntu.com/ubuntu bionic-updates InRelease
Hit:4 http://archive.ubuntu.com/ubuntu bionic-backports InRelease
Hit:5 http://archive.ubuntu.com/ubuntu bionic-security InRelease
Reading package lists... Done
N: Download is performed unsandboxed as root as file '/root/xcat-core/dists/bionic/InRelease' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
W: GPG error: file:/root/xcat-core bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F6F63590468E54F8
E: The repository 'file:/root/xcat-core bionic InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details

I try several different VM with different versions of xcat-core.

I also try with different keys downloaded from the xcat site.

I also try with an ubuntu 24.04 but give up because I learn that apt-key
is deprecated for this version and don't know how to deal with it.

Each time, I had the same issue... "The following signatures couldn't be verified..."

I also try using the flag " apt-get --allow-unauthenticated" ... same error message.

What do I miss ? Can you give me some hints ?
sincerely yours
Denis