ubuntu 16.04更新报错：
sudo apt-get update
命中:1 /ubuntu xenial InRelease
命中:2 /ubuntu xenial-security InRelease
命中:3 /ubuntu xenial-updates InRelease
命中:4 /ubuntu xenial-proposed InRelease
命中:5 /ubuntu xenial-backports InRelease
命中:6 /docker-engine/apt/repo ubuntu-xenial InRelease
获取:7 /repos/vscode stable InRelease [2,802 B]
命中:8 /linux/ubuntu xenial InRelease
获取:9 /ubuntu xenial-security InRelease [107 kB]
获取:10 /libnvidia-container/ubuntu16.04/amd64 InRelease [1,106 B]
获取:11 /nvidia-container-runtime/ubuntu16.04/amd64 InRelease [1,136 B]
获取:12 /nvidia-docker/ubuntu16.04/amd64 InRelease [1,129 B]
命中:13 /ubuntu xenial InRelease
获取:14 /repos/vscode stable/main amd64 Packages [70.4 kB]
获取:15 /ubuntu xenial-updates InRelease [109 kB]
命中:16 /node_6.x xenial InRelease
错误:10 /libnvidia-container/ubuntu16.04/amd64 InRelease
下列签名无效： KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 1538166745
错误:11 /nvidia-container-runtime/ubuntu16.04/amd64 InRelease
下列签名无效： KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 1538166745
错误:12 /nvidia-docker/ubuntu16.04/amd64 InRelease
下列签名无效： KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 1538166745
命中:17 /ethereum/ethereum-dev/ubuntu xenial InRelease
命中:18 /ethereum/ethereum/ubuntu xenial InRelease
获取:19 /ubuntu xenial-backports InRelease [107 kB]
获取:20 /ubuntu xenial-security/main amd64 DEP-11 Metadata [67.7 kB]
获取:21 /ubuntu xenial-security/main DEP-11 64x64 Icons [68.0 kB]
获取:22 /ubuntu xenial-security/universe amd64 DEP-11 Metadata [108 kB]
获取:23 /ubuntu xenial-updates/main amd64 Packages [856 kB]
获取:24 /ubuntu xenial-security/universe DEP-11 64x64 Icons [150 kB]
忽略:25 /sbt/debian InRelease
获取:26 /ubuntu xenial-updates/main i386 Packages [767 kB]
获取:27 /ubuntu xenial-updates/main amd64 DEP-11 Metadata [320 kB]
获取:28 /ubuntu xenial-updates/main DEP-11 64x64 Icons [227 kB]
获取:29 /ubuntu xenial-updates/universe amd64 Packages [690 kB]
获取:30 /ubuntu xenial-updates/universe i386 Packages [632 kB]
获取:31 /ubuntu xenial-updates/universe amd64 DEP-11 Metadata [247 kB]
获取:32 /ubuntu xenial-updates/universe DEP-11 64x64 Icons [333 kB]
获取:33 /sbt/debian Release [815 B]
命中:33 /sbt/debian Release
获取:35 /ubuntu xenial-updates/multiverse amd64 DEP-11 Metadata [5,960 B]
获取:36 /ubuntu xenial-updates/multiverse DEP-11 64x64 Icons [14.3 kB]
获取:37 /ubuntu xenial-backports/main amd64 DEP-11 Metadata [3,328 B]
获取:38 /ubuntu xenial-backports/universe amd64 DEP-11 Metadata [5,104 B]
错误:39 /mrtazz/restclient-cpp/ubuntu xenial InRelease
Connection timed out after 120990 milliseconds
已下载 4,894 kB，耗时 2分 3秒 (39.8 kB/s)
正在读取软件包列表... 完成
W: 校验数字签名时出错。此仓库未被更新，所以仍然使用此前的索引文件。GPG 错误：/libnvidia-container/ubuntu16.04/amd64 InRelease: 下列签名无效：
KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 1538166745W: 校验数字签名时出错。此仓库未被更新，所以仍然使用此前的索引文件。GPG 错误：/nvidia-container-runtime/ubuntu16.04/amd64 InRelease: 下列签名
无效： KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 1538166745W: 校验数字签名时出错。此仓库未被更新，所以仍然使用此前的索引文件。GPG 错误：/nvidia-docker/ubuntu16.04/amd64 InRelease: 下列签名无效： KEYEX
PIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 1538166745W: 无法下载 /mrtazz/restclient-cpp/ubuntu/dists/xenial/InRelease Connection timed out after 120990 milliseconds
W: 无法下载 /libnvidia-container/ubuntu16.04/amd64/InRelease 下列签名无效： KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 15381667
45 KEYEXPIRED 1538166745W: 无法下载 /nvidia-container-runtime/ubuntu16.04/amd64/InRelease 下列签名无效： KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 153
8166745 KEYEXPIRED 1538166745W: 无法下载 /nvidia-docker/ubuntu16.04/amd64/InRelease 下列签名无效： KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 KE
YEXPIRED 1538166745W: 部分索引文件下载失败。如果忽略它们，那将转而使用旧的索引文件。
表明密钥过期，需要更新
参考 ubuntu 12.04下owncloud更新出现KEYEXPIRED解决方法 ，KEYEXPIRED for OwnCloud Ubuntu Package。
最终，在 nvidia 镜像站找到更新 key的方法，参考 libnvidia-container： 的 Updating repository keys 的 Debian-based distributions
curl -s -L /libnvidia-container/gpgkey | \
sudo apt-key add -
试着更新一下：
$ curl -s -L /libnvidia-container/gpgkey | \
> sudo apt-key add -
OK
再更新软件：
$ sudo apt-get update
命中:1 /ubuntu xenial InRelease
命中:2 /ubuntu xenial-security InRelease
命中:3 /ubuntu xenial-updates InRelease
命中:4 /ubuntu xenial-proposed InRelease
命中:5 /ubuntu xenial-backports InRelease
命中:6 /docker-engine/apt/repo ubuntu-xenial InRelease
获取:7 /libnvidia-container/ubuntu16.04/amd64 InRelease [1,106 B]
获取:8 /nvidia-container-runtime/ubuntu16.04/amd64 InRelease [1,136 B]
命中:9 /repos/vscode stable InRelease
命中:10 /ubuntu xenial InRelease
获取:11 /nvidia-docker/ubuntu16.04/amd64 InRelease [1,129 B]
命中:12 /ubuntu xenial-security InRelease
命中:13 /linux/ubuntu xenial InRelease
命中:14 /ethereum/ethereum-dev/ubuntu xenial InRelease
命中:15 /ubuntu xenial-updates InRelease
命中:16 /node_6.x xenial InRelease
命中:17 /ubuntu xenial-backports InRelease
命中:18 /ethereum/ethereum/ubuntu xenial InRelease
忽略:19 /sbt/debian InRelease
获取:20 /sbt/debian Release [815 B]
命中:20 /sbt/debian Release
命中:22 /mrtazz/restclient-cpp/ubuntu xenial InRelease
已下载 3,371 B，耗时 33秒 (99 B/s)
正在读取软件包列表... 完成
done!