禁用更新

修改/etc/update-manager/release-upgrades中的配置项Prompt=lts为Prompt=never

$ sed -i s/Prompt=lts/Prompt=never/g /etc/update-manager/release-upgrades

清除缓存

删除/var/lib/ubuntu-release-upgrader/release-upgrade-available文件

$ rm /var/lib/ubuntu-release-upgrader/release-upgrade-available

重启

$ reboot