In case of a misbehaving OS update, it is possible to temporarily or permanently switch back to the previous working OS version. This is a manual operation which requires human intervention and console access.
Upon updates, the previous OS deployment is kept on disk so that it can be used as a fallback if something goes wrong.
In order to temporarily boot into the previous OS deployment, hold down
Shift during OS bootup and select the relevant OS entry in the bootloader menu.
The default boot configuration is not affected by this action, and the next reboot will select again the updated OS.
In order to permanently revert to the previous OS deployment, login to the target node and run
rpm-ostree rollback -r.
This operation will update boot-loader configuration, marking the previous OS deployment as the default one and immediately rebooting into it.