This is just a reminder to always enable docker service at system boot.
Preliminary information
Operating system version.
$ lsb_release -a
No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 20.04 LTS Release: 20.04 Codename: focal
Installed docker package.
$ apt-cache policy docker.io
docker.io:
Installed: 19.03.8-0ubuntu1.20.04
Candidate: 19.03.8-0ubuntu1.20.04
Version table:
*** 19.03.8-0ubuntu1.20.04 500
500 http://archive.ubuntu.com/ubuntu focal-updates/universe amd64 Packages
100 /var/lib/dpkg/status
19.03.8-0ubuntu1 500
500 http://archive.ubuntu.com/ubuntu focal/universe amd64 Packages
Docker details.
$ docker version
Client: Version: 19.03.8 API version: 1.40 Go version: go1.13.8 Git commit: afacb8b7f0 Built: Tue Jun 23 22:26:12 2020 OS/Arch: linux/amd64 Experimental: false Server: Engine: Version: 19.03.8 API version: 1.40 (minimum version 1.12) Go version: go1.13.8 Git commit: afacb8b7f0 Built: Thu Jun 18 08:26:54 2020 OS/Arch: linux/amd64 Experimental: false containerd: Version: 1.3.3-0ubuntu2 GitCommit: runc: Version: spec: 1.0.1-dev GitCommit: docker-init: Version: 0.18.0 GitCommit:
The problem
After system reboot docker service is stopped.
$ systemctl status docker
● docker.service - Docker Application Container Engine
Loaded: loaded (/lib/systemd/system/docker.service; disabled; vendor preset: enabled)
Active: inactive (dead)
TriggeredBy: ● docker.socket
Docs: https://docs.docker.com
It will start after executing docker command-line utility.
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
This is because it is triggered by the docker socket.
$ systemctl status docker
● docker.service - Docker Application Container Engine
Loaded: loaded (/lib/systemd/system/docker.service; disabled; vendor preset: enabled)
Active: active (running) since Sat 2020-07-18 11:10:13 UTC; 24s ago
TriggeredBy: ● docker.socket
Docs: https://docs.docker.com
Main PID: 265 (dockerd)
Tasks: 21
Memory: 102.3M
CGroup: /system.slice/docker.service
└─265 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
Jul 18 11:10:13 swarm-kraken dockerd[265]: time="2020-07-18T11:10:13.753469409Z" level=info msg="API listen on /run/docker.sock"
Jul 18 11:10:13 swarm-kraken systemd[1]: Started Docker Application Container Engine.
Inspect docker service file to see how it is triggered.
$ cat /lib/systemd/system/docker.service
[Unit] Description=Docker Application Container Engine Documentation=https://docs.docker.com BindsTo=containerd.service After=network-online.target firewalld.service containerd.service Wants=network-online.target 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 TimeoutSec=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 [Install] WantedBy=multi-user.target
Inspect docker socket file to see how it defined.
$ systemctl status docker.socket
● docker.socket - Docker Socket for the API
Loaded: loaded (/lib/systemd/system/docker.socket; enabled; vendor preset: enabled)
Active: active (running) since Sat 2020-07-18 11:06:51 UTC; 4min 33s ago
Triggers: ● docker.service
Listen: /run/docker.sock (Stream)
Tasks: 0 (limit: 38388)
Memory: 0B
CGroup: /system.slice/docker.socket
Jul 18 11:06:51 swarm-kraken systemd[1]: Starting Docker Socket for the API.
Jul 18 11:06:51 swarm-kraken systemd[1]: Listening on Docker Socket for the API.
$ cat /lib/systemd/system/docker.socket
[Unit] Description=Docker Socket for the API PartOf=docker.service [Socket] ListenStream=/var/run/docker.sock SocketMode=0660 SocketUser=root SocketGroup=docker [Install] WantedBy=sockets.target
The solution
As you may have noticed, docker service is disabled by default.
$ systemctl is-enabled docker
disabled
Enable docker service and start it immediately.
$ sudo systemctl enable --now docker
Created symlink /etc/systemd/system/multi-user.target.wants/docker.service → /lib/systemd/system/docker.service.
$ sudo systemctl status docker
● docker.service - Docker Application Container Engine
Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
Active: active (running) since Sat 2020-07-18 11:14:05 UTC; 15s ago
TriggeredBy: ● docker.socket
Docs: https://docs.docker.com
Main PID: 263 (dockerd)
Tasks: 20
Memory: 100.4M
CGroup: /system.slice/docker.service
└─263 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
Jul 18 11:14:05 swarm-kraken dockerd[263]: time="2020-07-18T11:14:05.713787002Z" level=info msg="API listen on /run/docker.sock"
Jul 18 11:14:05 swarm-kraken systemd[1]: Started Docker Application Container Engine.
Now, it will perform as expected.