Hello @lah7 !
Thank you for your answer. As I said, i followed this page to upgrade which seems to be an official way given by @wolfman : How to upgrade Ubuntu (Mate) via the terminal
lsb_release -a
gives :
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04 LTS
Release: 16.04
Codename: xenial
My PPAs active in Software&Updates ( i deleted other few hours ago)
