Detailed troubleshooting of docker.service startup errors

Execute the following command to report an error

systemctl restart docker

View error messages

systemctl status docker -l

The error message is as follows:

● docker.service - Docker Application Container Engine
  Loaded: loaded (/usr/lib/systemd/system/docker.service; disabled; vendor preset: disabled)
 Drop-In: /etc/systemd/system/docker.service.d
      └─kolla.conf
  Active: failed (Result: exit-code) since Wednesday 2018-08-01 16:32:27 CST; 52 minutes ago
   Docs: https://docs.docker.com
 Process: 3833722 ExecStart=/usr/bin/docker daemon --insecure-registry 172.16.59.153 (code=exited, status=1/FAILURE)
 Main PID: 3833722 (code=exited, status=1/FAILURE)
  Memory: 8.0K
  CGroup: /system.slice/docker.service

Aug 01 16:32:26 czwei004 systemd[1]: Starting Docker Application Container Engine...
August 01 16:32:26 czwei004 docker[3833722]: time="2018-08-01T16:32:26.527063936+08:00" level=info msg="libcontainerd: new containerd process, pid: 3833733"
Aug 01 16:32:27 czwei004 docker[3833722]: time="2018-08-01T16:32:27.532317497+08:00" level=warning msg="devmapper: Usage of loopback devices is strongly discouraged for production use. Please use `--storage-opt dm.thinpooldev` or use `man docker` to refer to dm.thinpooldev section."
Aug 01 16:32:27 czwei004 docker[3833722]: time="2018-08-01T16:32:27.560010414+08:00" level=warning msg="devmapper: Base device already exists and has filesystem xfs on it. User specified filesystem will be ignored."
August 01 16:32:27 czwei004 docker[3833722]: time="2018-08-01T16:32:27.577758251+08:00" level=fatal msg="Error starting daemon: error initializing graphdriver: \"/var/lib/docker\" contains several valid graphdrivers: devicemapper, overlay2; Please cleanup or explicitly choose storage driver (-s <DRIVER>)"
Aug 01 16:32:27 czwei004 systemd[1]: docker.service: main process exited, code=exited, status=1/FAILURE
Aug 01 16:32:27 czwei004 systemd[1]: Failed to start Docker Application Container Engine.
Aug 01 16:32:27 czwei004 systemd[1]: Unit docker.service entered failed state.
Aug 01 16:32:27 czwei004 systemd[1]: docker.service failed.

Note that in the above error message

msg="Error starting daemon: error initializing graphdriver: \"/var/lib/docker\" contains several valid graphdrivers: devicemapper, overlay2; Please cleanup or explicitly choose storage driver (-s <DRIVER>)"

Go to the docker directory and check, there are directories for devicemapper and overlay2

The reason is that I installed a higher version of docker-engine before, and the default storage driver is overlay2. When I uninstalled it, the overlay2 folder remained in the docker directory. Later, I installed a lower version of docker, and the default was devicemapper, so there were multiple storage drivers.

After restarting the machine, delete the overlay2 directory and you can start it.

Additional knowledge: CentOS7 modifies the default storage location of Docker images

Stop the Docker service

# systemctl stop docker

Modify the docker service startup file

# vim /etc/sysconfig/docker

OPTIONS='--selinux-enabled --log-driver=journald --graph=/docker --signature-verification=false --insecure-registry 192.168.1.1'
#--insecure-registry 192.168.1.1 This is the warehouse address and can be ignored. # The /docker directory is what I use to replace the default /var/lib/docker. After the directory is created, remember to "mv /var/lib/docker/* /docker/" to move all the original

Copy all the files and directories in the first directory to the new directory.

Reload the configuration and start

# systemctl daemon-reload
# systemctl start docker

Check docker information

# docker info

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