1. $ sudo docker pull fedora:20
    2. [sudo] jdxj 的密码：
    3. 20: Pulling from library/fedora
    4. 4abd98c7489c: Pull complete 
    5. Digest: sha256:5d5a02b873d298da9bca4b84440c5cd698b0832560c850d92cf389cef58bc549
    6. Status: Downloaded newer image for fedora:20
    7. docker.io/library/fedora:20
    1. $ sudo docker images fedora
    2. REPOSITORY   TAG       IMAGE ID       CREATED       SIZE
    3. fedora       20        ba74bddb630e   4 years ago   291MB