（作者：陈玓玏）
1、给我一个必须修改镜像的理由
安装好docker后，意欲试用一下docker，于是输入sudo docker run hello-world，结果提示：
Unable to find image 'hello-world:latest' locally
docker: Error response from daemon: Get https://registry-1.docker.io/v2/: dial tcp: lookup registry-1.docker.io on 127.0.1.1:53: read udp 127.0.0.1:54341->127.0.1.1:53: i/o timeout.
See 'docker run --help'也就是说，找不到镜像，于是尝试找一下镜像：
sudo docker search hello-world提示：
Warning: failed to get default registry endpoint from daemon (Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.38/info: dial unix /var/run/docker.sock: connect: permission denied). Using system default: https://index.docker.io/v1/
Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.38/images/search?limit=25&term=hello-world: dial unix /var/run/docker.sock: connect: permission denied于是尝试找一个绝对不可能找不到的镜像;
sudo docker search ubuntu结果提示：
Error response from daemon: Get https://index.docker.io/v1/search?q=ubuntu&n=25: dial tcp: lookup index.docker.io on 127.0.1.1:53: read udp 127.0.0.1:60246->127.0.1.1:53: i/o timeout这下小伙伴说，必须修改镜像源才行了，现在的镜像用不了，连接以后速度太慢，总是会出现timeout错误。
2、怎么修改镜像源
我当前是root用户，所以不用加sudo。
1）打开配置文件
gedit /etc/docker/daemon.json2）修改配置文件
这里用的是网易的镜像，你也可以用阿里的、豆瓣的，还有一些学校的，像中科大、清华什么的，只要把那个网址改掉就好了。改完之后把文件保存好。
{
"registry-mirrors": ["http://hub-mirror.c.163.com"]
}3）检查修改效果
输入
docker search ubuntu结果如下，说明成功了;
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NAME DESCRIPTION STARS OFFICIAL AUTOMATED
ubuntu Ubuntu is a Debian-based Linux operating sys… 8242 [OK]
dorowu/ubuntu-desktop-lxde-vnc Ubuntu with openssh-server and NoVNC 212 [OK]
rastasheep/ubuntu-sshd Dockerized SSH service, built on top of offi… 167 [OK]
consol/ubuntu-xfce-vnc Ubuntu container with "headless" VNC session… 126 [OK]
ansible/ubuntu14.04-ansible Ubuntu 14.04 LTS with ansible 95 [OK]
ubuntu-upstart Upstart is an event-based replacement for th… 87 [OK]
neurodebian NeuroDebian provides neuroscience research s… 52 [OK]
1and1internet/ubuntu-16-nginx-php-phpmyadmin-mysql-5 ubuntu-16-nginx-php-phpmyadmin-mysql-5 43 [OK]
ubuntu-debootstrap debootstrap --variant=minbase --components=m… 39 [OK]
nuagebec/ubuntu Simple always updated Ubuntu docker images w… 23 [OK]
tutum/ubuntu Simple Ubuntu docker images with SSH access 18
i386/ubuntu Ubuntu is a Debian-based Linux operating sys… 13
ppc64le/ubuntu Ubuntu is a Debian-based Linux operating sys… 12
1and1internet/ubuntu-16-apache-php-7.0 ubuntu-16-apache-php-7.0 12 [OK]
eclipse/ubuntu_jdk8 Ubuntu, JDK8, Maven 3, git, curl, nmap, mc, … 6 [OK]
codenvy/ubuntu_jdk8 Ubuntu, JDK8, Maven 3, git, curl, nmap, mc, … 4 [OK]
darksheer/ubuntu Base Ubuntu Image -- Updated hourly 4 [OK]
1and1internet/ubuntu-16-nginx-php-5.6-wordpress-4 ubuntu-16-nginx-php-5.6-wordpress-4 3 [OK]
1and1internet/ubuntu-16-sshd ubuntu-16-sshd 1 [OK]
pivotaldata/ubuntu A quick freshening-up of the base Ubuntu doc… 1
ossobv/ubuntu Custom ubuntu image from scratch (based on o… 0
1and1internet/ubuntu-16-healthcheck ubuntu-16-healthcheck 0 [OK]
1and1internet/ubuntu-16-rspec ubuntu-16-rspec 0 [OK]
smartentry/ubuntu ubuntu with smartentry 0 [OK]
pivotaldata/ubuntu-gpdb-dev Ubuntu images for GPDB development 0