问题：拉取docker镜像时提示no space left on device问题解决 (centos7.2)
    解决方式：出现此问题一般是Docker Root Dir目录空间不足导致。可修改其 **Docker Root Dir** 的值，使其指向一个更大空间的目录即可

    • ①：查看docker的根目录：

      docker的默认目录为：Docker Root Dir: /var/lib/docker

    1. [root@localhost ~]# docker info 
    2. Client:
    3.  Context:    default
    4.  Debug Mode: false
    5.  Plugins:
    6.   app: Docker App (Docker Inc., v0.9.1-beta3)
    7.   buildx: Build with BuildKit (Docker Inc., v0.5.1-docker)
    8.   scan: Docker Scan (Docker Inc.)
    10. Server:
    11.  Containers: 2
    12.   Running: 0
    13.   Paused: 0
    14.   Stopped: 2
    15.  Images: 2
    16.  Server Version: 20.10.6
    17.  Storage Driver: overlay2
    18.   Backing Filesystem: xfs
    19.   Supports d_type: true
    20.   Native Overlay Diff: true
    21.   userxattr: false
    22.  Logging Driver: json-file
    23.  Cgroup Driver: cgroupfs
    24.  Cgroup Version: 1
    25.  Plugins:
    26.   Volume: local
    27.   Network: bridge host ipvlan macvlan null overlay
    28.   Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
    29.  Swarm: inactive
    30.  Runtimes: io.containerd.runc.v2 io.containerd.runtime.v1.linux runc
    31.  Default Runtime: runc
    32.  Init Binary: docker-init
    33.  containerd version: 05f951a3781f4f2c1911b05e61c160e9c30eaa8e
    34.  runc version: 12644e614e25b05da6fd08a38ffa0cfe1903fdec
    35.  init version: de40ad0
    36.  Security Options:
    37.   seccomp
    38.    Profile: default
    39.  Kernel Version: 3.10.0-957.el7.x86_64
    40.  Operating System: CentOS Linux 7 (Core)
    41.  OSType: linux
    42.  Architecture: x86_64
    43.  CPUs: 24
    44.  Total Memory: 31.2GiB
    45.  Name: localhost.localdomain
    46.  ID: J6CE:BNRP:HJOO:PHQU:S47A:YEY7:5I6A:CE4B:VPSA:6BRN:7EH3:3UJB
    47.  Docker Root Dir: /var/lib/docker
    48.  Debug Mode: false
    49.  Registry: https://index.docker.io/v1/
    50.  Labels:
    51.  Experimental: false
    52.  Insecure Registries:
    53.   127.0.0.0/8
    54.  Live Restore Enabled: false

    • ②：查看docker的默认var/lib/docker目录所剩余空间：

      1. [root@localhost ~]# df  -hl   /var/lib/docker/
      2. Filesystem               Size  Used Avail Use% Mounted on
      3. /dev/mapper/centos-root   50G   39G   12G  78% /

    • ③：发现/home目录空间容量很大，可以将Docker Root Dir指向到此处：

      1. [root@localhost ~]# df -h
      2. Filesystem               Size  Used Avail Use% Mounted on
      3. /dev/mapper/centos-root   50G   39G   12G  78% /
      4. devtmpfs                  16G     0   16G   0% /dev
      5. tmpfs                     16G  4.0K   16G   1% /dev/shm
      6. tmpfs                     16G  1.6G   15G  10% /run
      7. tmpfs                     16G     0   16G   0% /sys/fs/cgroup
      8. /dev/mapper/centos-home  234G  6.1G  228G   3% /home
      9. /dev/sda1               1014M  146M  869M  15% /boot
      10. tmpfs                    3.2G     0  3.2G   0% /run/user/26
      11. tmpfs                    3.2G     0  3.2G   0% /run/user/0

    • ④：创建/home/docker/lib/docker目录，修改Docker Root Dir: /home/docker/lib/docker：

      1. [root@localhost ~]# mkdir -p /home/docker/lib/docker

    • ⑤：创建devicemapper.conf配置文件：

      1. [root@localhost ~]# mkdir -p /etc/systemd/system/docker.service.d/
      2. [root@localhost ~]# 
      3. [root@localhost ~]#
      4. [root@localhost ~]# vim /etc/systemd/system/docker.service.d/devicemapper.conf

    • ⑥：配置devicemapper.conf文件内容，内如如下：

      1. [Service]
      2. ExecStart=
      3. ExecStart=/usr/bin/dockerd  --graph=/home/docker/lib/docker

    • ⑦：重启docker：

      1. [root@localhost ~]# sudo systemctl daemon-reload
      2. [root@localhost ~]
      3. [root@localhost ~]# sudo systemctl restart docker

    ⑧：注意，由于更换了Docker Root Dir目录，以前下载的镜像需要转移到新目录下，本人通过cp -R命令复制过来后，启动时遇到一些问题，建议直接删除原来的镜像，重新下载。

    文章参考连接：

    • 拉取docker镜像时提示 no space left on device 问题解决：https://www.cnblogs.com/lostvip/p/9909689.html