Jan 17 01:18:56 localhost.localdomain systemd[1]: docker.service failed.
Jan 17 01:18:59 localhost.localdomain systemd[1]: docker.service holdoff time over, scheduling restart.
Jan 17 01:18:59 localhost.localdomain systemd[1]: Stopped Docker Application Container Engine.
Jan 17 01:18:59 localhost.localdomain systemd[1]: start request repeated too quickly for docker.service
Jan 17 01:18:59 localhost.localdomain systemd[1]: Failed to start Docker Application Container Engine.
Jan 17 01:18:59 localhost.localdomain systemd[1]: Unit docker.service entered failed state.
Jan 17 01:18:59 localhost.localdomain systemd[1]: docker.service failed.
Jan 17 01:20:37 localhost.localdomain systemd[1]: docker.service has more than one ExecStart= setting, wh...ing.
Jan 17 01:21:34 localhost.localdomain systemd[1]: docker.service has more than one ExecStart= setting, wh...ing.
Jan 17 01:23:46 localhost.localdomain systemd[1]: docker.service has more than one ExecStart= setting, wh...ing.
Hint: Some lines were ellipsized, use -l to show in full.
解决：
升级内核：
[root@localhost docker.service.d]# yum update -y
升级完成后，卸载旧版本，重新安装docker-ce。
[root@localhost docker.service.d]# rpm -qa |grep docker-ce
docker-ce-19.03.5-3.el7.x86_64
docker-ce-cli-19.03.5-3.el7.x86_64
[root@localhost docker.service.d]# rpm -e --nodeps docker-ce-19.03.5-3.el7.x86_64
[root@localhost docker.service.d]# rpm -e --nodeps docker-ce-cli-19.03.5-3.el7.x86_64
[root@localhost docker.service.d]# yum install -y docker-ce-*
[root@localhost docker.service.d]# systemctl start docker
[root@localhost docker.service.d]# systemctl status docker
docker正常启动！！！！
反思：是否可以先安装flannel，再按照docker-ce，是否会出现类似的情况？待测试！！！！
问题二：docker、flannel正常启动，但docker0无法获取地址池地址。
解决：
修改/usr/lib/systemd/system/docker.service文件
[root@localhost docker.service.d]# vim /usr/lib/systemd/system/docker.service
添加以下内容：
在ExecStart=/usr/bin/dockerd后添加$DOCKER_NETWORK_OPTIONS
在[server]最后添加
EnvironmentFile=/run/flannel/docker
重新启动docker
[root@localhost docker.service.d]# systemctl daemon-reload
[root@localhost docker.service.d]# systemctl restart docker.service
[root@localhost docker.service.d]# ifconfig 
docker0正常获取flannel地址池。
docker之docker容器flannel模式多网段跨主机通信所遇问题集
原文：https://blog.51cto.com/3001441/2467573