运行升级指令：
sudo dnf system-upgrade download --releasever=24
Repository fzug-free is listed more than once in the configuration
Repository fzug-free-source is listed more than once in the configuration
Repository fzug-nonfree is listed more than once in the configuration
Repository fzug-nonfree-source is listed more than once in the configuration
determining the fastest mirror (21 hosts).. done.
Fedora 24 - x86_64 - Updates 1.4 MB/s | 4.6 MB 00:03
Failed to synchronize cache for repo 'rpmfusion-nonfree-updates'，禁用。
Failed to synchronize cache for repo 'fzug-nonfree'，禁用。
Failed to synchronize cache for repo 'fzug-free'，禁用。
上次元数据过期检查：0:00:09 前，执行于 Wed Jun 25 23:12:00 2016。
依赖关系解决。
错误：该操作将导致移除已启动的内核：kernel-core-4.5.7-200.fc23.x86_64。
解决：升级第二步采用指令：sudo dnf system-upgrade download --releasever=24 --best --nogpgcheck --allowerasing