使用docker下载镜像时，出现下面错误： 

docker: Error response from daemon: Get https://registry-1.docker.io/v2/: net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers).

 刚开始以为是镜像源问题，更改后没有效果

1. # 操作系统：centos7

2. # 编辑daemon.json文件

3. vi /etc/docker/daemon.json

4. {

5. "registry-mirrors": ["https://docker.mirrors.ustc.edu.cn","https://registry.docker-cn.com","http://hub-mirror.c.163.com"]

6. }

8. # 重启docker

9. systemctl restart docker

接下来进行以下操作，解决了上述无法下载的问题

1. # 第一步：下载dig工具

2. yum install bind-utils

4. # 第二步：

5. dig @114.114.114.114 registry-1.docker.io

7. # 返回内容如下

8. ; <<>> DiG 9.11.4-P2-RedHat-9.11.4-16.P2.el7_8.2 <<>> @114.114.114.114 registry-1.docker.io

9. ; (1 server found)

10. ;; global options: +cmd

11. ;; Got answer:

12. ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 45192

13. ;; flags: qr rd ra; QUERY: 1, ANSWER: 8, AUTHORITY: 0, ADDITIONAL: 0

15. ;; QUESTION SECTION:

16. ;registry-1.docker.io. IN A

18. ;; ANSWER SECTION:

19. registry-1.docker.io. 1 IN A 34.197.211.151

20. registry-1.docker.io. 1 IN A 54.236.165.68

21. registry-1.docker.io. 1 IN A 34.192.204.44

22. registry-1.docker.io. 1 IN A 52.72.232.213

23. registry-1.docker.io. 1 IN A 18.214.230.110

24. registry-1.docker.io. 1 IN A 34.198.213.42

25. registry-1.docker.io. 1 IN A 107.23.149.57

26. registry-1.docker.io. 1 IN A 52.204.76.244

28. ;; Query time: 5 msec

29. ;; SERVER: 114.114.114.114#53(114.114.114.114)

30. ;; WHEN: Fri Dec 18 20:08:55 CST 2020

31. ;; MSG SIZE rcvd: 166

34. # 第三步：接下来我们只需要把以下信息追加到/etc/hosts

35. 34.197.211.151 registry-1.docker.io

36. 54.236.165.68 registry-1.docker.io

37. 34.192.204.44 registry-1.docker.io

38. 52.72.232.213 registry-1.docker.io

39. 18.214.230.110 registry-1.docker.io

40. 34.198.213.42 registry-1.docker.io

41. 107.23.149.57 registry-1.docker.io

42. 52.204.76.244 registry-1.docker.io

接下来docker pull xx镜像，没有报错就可以正常拉取镜像了。

不过，可能会出现证书过期或无效的报错（一般是本地系统时间错误导致报错证书过期）

docker: Error response from daemon: Get https://registry-1.docker.io/v2/: x509: certificate has expired or is not yet valid.

1. # 安装

2. yum install ntpdate

4. # 同步时间

5. ntpdate cn.pool.ntp.org