最近遇到一台服务器重启后docker.service无法启动，记录解决过程。

问题现象

1.执行<code>docker ps后，终端报错如下：

Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

2.执行systemctl status docker查看详细信息如下：

解决过程

1. 检查docker.service和docker.socket文件是否异常

不看不知道，一看吓一跳，好家伙，这台服务器上这两个文件都不翼而飞，于是从另一台docker功能正常的服务器拷贝上述两个文件到本机，由于docker安装时未修改默认配置，所以两个文件均未修改.

1.1. 修改docker.service

执行<code>vim /lib/systemd/system/docker.service，添加以下内容：

[Unit]

Description=Docker Application Container Engine

Documentation=https://docs.docker.com

After=network-online.target docker.socket firewalld.service containerd.service time-set.target

Wants=network-online.target containerd.service

Requires=docker.socket

[Service]

Type=notify

# the default is not to use systemd for cgroups because the delegate issues still

# exists and systemd currently does not support the cgroup feature set required

# for containers run by docker

ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

ExecReload=/bin/kill -s HUP $MAINPID

TimeoutStartSec=0

RestartSec=2

Restart=always

# Note that StartLimit* options were moved from "Service" to "Unit" in systemd 229.

# Both the old, and new location are accepted by systemd 229 and up, so using the old location

# to make them work for either version of systemd.

StartLimitBurst=3

# Note that StartLimitInterval was renamed to StartLimitIntervalSec in systemd 230.

# Both the old, and new name are accepted by systemd 230 and up, so using the old name to make

# this option work for either version of systemd.

StartLimitInterval=60s

# Having non-zero Limit*s causes performance problems due to accounting overhead

# in the kernel. We recommend using cgroups to do container-local accounting.

LimitNOFILE=infinity

LimitNPROC=infinity

LimitCORE=infinity

# Comment TasksMax if your systemd version does not support it.

# Only systemd 226 and above support this option.

TasksMax=infinity

# set delegate yes so that systemd does not reset the cgroups of docker containers

Delegate=yes

# kill only the docker process, not all processes in the cgroup

KillMode=process

OOMScoreAdjust=-500

[Install]

WantedBy=multi-user.target

1.2. 修改docker.socket

执行vim /lib/systemd/system/docker.socket，添加以下内容：

vim /lib/systemd/system/docker.socket

[Unit]

Description=Docker Socket for the API

[Socket]

# If /var/run is not implemented as a symlink to /run, you may need to

# specify ListenStream=/var/run/docker.sock instead.

ListenStream=/run/docker.sock

SocketMode=0660

SocketUser=root

SocketGroup=docker

[Install]

WantedBy=sockets.target

2. 重启docker

systemctl daemon-reload

systemctl restart docker

# 验证是否修复

docker ps

# 相同报错

Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

执行以上命令重启docker后，发现报错还在，执行journalctl -u docker.service -f查看docker服务详细信息，终端输出如下：

3. 检查containerd

执行命令<code>which containerd， 发现服务器未安装containerd，执行以下命令安装

## 安装containerd

apt-get install containerd

## 再次查看

which containerd

## 输出如下

/usr/bin/containerd

4. 执行步骤2，再次重启docker

docker重启后，执行docker ps，此时docker已经可以正常使用：

5. 另一个小问题

使用过程中发现docker命令的tab键命令补全功能失效，在网上找到了解决方式：

<code>## 1.下载自动补全脚本：

curl -o /etc/bash_completion.d/docker https://raw.githubusercontent.com/docker/cli/master/contrib/completion/bash/docker

## 2.重新加载bash配置：

source /etc/bash_completion.d/docker

至此，该问题已修复，docker可正常使用