Problem reboot to upgrade from 26 to 27

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Hi everyone,

I followed every steps described on the fedora magazine website to upgrade my Fedora Spins Cinnamon from 26 to 27, and all 3 command to get upgrades went okay (one downloaded like 1k upgrades, around 1.6G so I assume this is okay).

When I use the command to reboot and do upgrade, it goes to where the upgrade should start, just after the fedora build to choose (here 26 as it's not installed yet). Then I got my normal cpu over temperature (never caused problems, even to install 26 one week ago), and I barely see a message popping then it reboot again. From there, back to 26 like everyday.

What can I do to troubleshoot this ?

Edit - Using journalctl -b -1

systemd[1]: Starting System Upgrade using DNF...
dnf[711]: Erreur : Échec de la synchronisation du cache pour le dépôt « updates »
systemd[1]: dnf-system-upgrade.service: Main process exited, code=exited, status=1/FAILURE
systemd[1]: Failed to start System Upgrade using DNF.
systemd[1]: dnf-system-upgrade.service: Unit entered failed state.
kernel: audit: type=1130 audit(1510938551.521:81): pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=dnf-system-upgrade comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=failed'
audit[1]: SERVICE_START pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=dnf-system-upgrade comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=failed'
systemd[1]: dnf-system-upgrade.service: Failed with result 'exit-code'.
systemd[1]: Rebooting: service failed