sudo apt update报错

在Ubuntu系统下，使用sudo apt-get update有时会出现“W: 无法下载 http://cn.archive.ubuntu.com/ubuntu/.... 校验和不符”，

xj@xjVir:~/test$ sudo apt-get update
获取:1 http://security.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB]
获取:2 http://cn.archive.ubuntu.com/ubuntu bionic InRelease [242 kB]
获取:3 http://security.ubuntu.com/ubuntu bionic-security/main amd64 Packages [573 kB]
获取:4 http://security.ubuntu.com/ubuntu bionic-security/main i386 Packages [404 kB]
错误:2 http://cn.archive.ubuntu.com/ubuntu bionic InRelease                    
  连接超时 [IP: 91.189.91.24 80]
获取:5 http://cn.archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]  
忽略:4 http://security.ubuntu.com/ubuntu bionic-security/main i386 Packages    
获取:6 http://security.ubuntu.com/ubuntu bionic-security/main Translation-en [190 kB]
获取:7 http://security.ubuntu.com/ubuntu bionic-security/main amd64 DEP-11 Metadata [38.5 kB]
获取:8 http://security.ubuntu.com/ubuntu bionic-security/main DEP-11 48x48 Icons [17.6 kB]
获取:9 http://security.ubuntu.com/ubuntu bionic-security/main DEP-11 64x64 Icons [41.5 kB]
错误:5 http://cn.archive.ubuntu.com/ubuntu bionic-updates InRelease            
  连接超时 [IP: 91.189.91.24 80]
获取:10 http://cn.archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB]
获取:11 http://security.ubuntu.com/ubuntu bionic-security/restricted amd64 Packages [13.2 kB]
获取:12 http://security.ubuntu.com/ubuntu bionic-security/restricted i386 Packages [4,280 B]
获取:13 http://security.ubuntu.com/ubuntu bionic-security/restricted Translation-en [4,292 B]
获取:14 http://security.ubuntu.com/ubuntu bionic-security/universe amd64 Packages [621 kB]
忽略:14 http://security.ubuntu.com/ubuntu bionic-security/universe amd64 Packages
获取:15 http://security.ubuntu.com/ubuntu bionic-security/universe i386 Packages [597 kB]
错误:10 http://cn.archive.ubuntu.com/ubuntu bionic-backports InRelease
  连接超时 [IP: 91.189.91.26 80]
获取:16 http://security.ubuntu.com/ubuntu bionic-security/universe Translation-en [207 kB]
忽略:16 http://security.ubuntu.com/ubuntu bionic-security/universe Translation-en
获取:17 http://security.ubuntu.com/ubuntu bionic-security/universe amd64 DEP-11 Metadata [42.1 kB]
获取:18 http://security.ubuntu.com/ubuntu bionic-security/universe DEP-11 48x48 Icons [16.4 kB]
获取:19 http://security.ubuntu.com/ubuntu bionic-security/universe DEP-11 64x64 Icons [111 kB]
获取:20 http://security.ubuntu.com/ubuntu bionic-security/multiverse i386 Packages [4,292 B]
获取:21 http://security.ubuntu.com/ubuntu bionic-security/multiverse amd64 Packages [5,904 B]
获取:22 http://security.ubuntu.com/ubuntu bionic-security/multiverse Translation-en [2,568 B]
获取:23 http://security.ubuntu.com/ubuntu bionic-security/multiverse amd64 DEP-11 Metadata [2,464 B]
获取:24 http://security.ubuntu.com/ubuntu bionic-security/multiverse DEP-11 48x48 Icons [29 B]
获取:25 http://security.ubuntu.com/ubuntu bionic-security/multiverse DEP-11 64x64 Icons [2,638 B]
获取:4 http://security.ubuntu.com/ubuntu bionic-security/main i386 Packages [404 kB]
获取:14 http://security.ubuntu.com/ubuntu bionic-security/universe amd64 Packages [621 kB]
获取:16 http://security.ubuntu.com/ubuntu bionic-security/universe Translation-en [207 kB]
已下载 2,987 kB，耗时 5分 3秒 (9,868 B/s)                                      
正在读取软件包列表... 完成
W: 无法下载 http://cn.archive.ubuntu.com/ubuntu/dists/bionic/InRelease  连接超时 [IP: 91.189.91.24 80]
W: 无法下载 http://cn.archive.ubuntu.com/ubuntu/dists/bionic-updates/InRelease  连接超时 [IP: 91.189.91.24 80]
W: 无法下载 http://cn.archive.ubuntu.com/ubuntu/dists/bionic-backports/InRelease  连接超时 [IP: 91.189.91.26 80]
W: 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。