Step 5: Install Docker

Docker Overview

Docker is a tool designed to make it easier to create, deploy, and run applications by using containers. Containers allow a developer to package up an application with all of the parts it needs, such as libraries and other dependencies, and ship it all out as one package. By doing so, thanks to the container, the developer can rest assured that the application will run on any other Linux machine regardless of any customized settings that machine might have that could differ from the machine used for writing and testing the code.

In a way, Docker is a bit like a virtual machine. But unlike a virtual machine, rather than creating a whole virtual operating system, Docker allows applications to use the same Linux kernel as the system that they’re running on and only requires applications to be shipped with things not already running on the host computer. This gives a significant performance boost and reduces the size of the application. Read more on opensource.com’s What is Docker? article.

View these pages to learn more about Docker

Install Docker

Docker is not installed by default. So, we must install it and then verify that it works properly.

There are several versions of docker. We will use docker.io because is easier to set up.

  1. We should refresh the apt packages to ensure that we are installing the latest version.

  2. Then, we will install docker.io using flag -y to install docker and any required packages automatically.

    sudo apt update
sudo apt install -y docker.io

     1 root@vps298933:~# sudo apt install docker.io
 2 Reading package lists... Done
 3 Building dependency tree
 4 Reading state information... Done
 5 The following additional packages will be installed:
 6 bridge-utils cgroupfs-mount libltdl7 pigz ubuntu-fan
 7 Suggested packages:
 8 ifupdown aufs-tools debootstrap docker-doc rinse zfs-fuse | zfsutils
 9 The following NEW packages will be installed:
10 bridge-utils cgroupfs-mount docker.io libltdl7 pigz ubuntu-fan
11 0 upgraded, 6 newly installed, 0 to remove and 0 not upgraded.
12 Need to get 40.3 MB of archives.
13 After this operation, 198 MB of additional disk space will be used.
14 Do you want to continue? [Y/n] y
15 Get:1 http://nova.clouds.archive.ubuntu.com/ubuntu bionic/universe amd64 pigz amd64 2.4-1 [57.4 kB]
16 Get:2 http://nova.clouds.archive.ubuntu.com/ubuntu bionic/main amd64 bridge-utils amd64 1.5-15ubuntu1 [30.1 kB]
17 Get:3 http://nova.clouds.archive.ubuntu.com/ubuntu bionic/universe amd64 cgroupfs-mount all 1.4 [6,320 B]
18 .
19 .
20 .
21 Setting up docker.io (18.06.1-0ubuntu1~18.04.1) ...
22 Adding group 'docker' (GID 115) ...
23 Done.
24 Created symlink /etc/systemd/system/sockets.target.wants/docker.socket ? /lib/systemd/system/docker.socket.
25 Processing triggers for ureadahead (0.100.0-20) ...
26 Processing triggers for libc-bin (2.27-3ubuntu1) ...
27 Processing triggers for systemd (237-3ubuntu10.11) ...
28 root@vps298933:~#

  3. Enable Docker so it will start on reboot

    sudo systemctl enable docker

    1 root@vps298933:~# sudo systemctl enable docker
2 Synchronizing state of docker.service with SysV service script with /lib/systemd/systemd-sysv-install.
3 Executing: /lib/systemd/systemd-sysv-install enable docker

  4. View the status of the application. You should see this line: Active: active (running)

    sudo systemctl status docker

     1  root@vps298933:~/sphinx-server#
 2  root@vps298933:~/sphinx-server# systemctl status docker
 3  ● docker.service - Docker Application Container Engine
 4  Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
 5  Active: active (running) since Sat 2019-03-16 11:18:56 +06; 3h 21min ago
 6      Docs: https://docs.docker.com
 7  Main PID: 900 (dockerd)
 8      Tasks: 15
 9  CGroup: /system.slice/docker.service
10          +-  900 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
11          +-10992 /usr/bin/docker-proxy -proto tcp -host-ip 0.0.0.0 -host-port 8000 -container-ip 172.17.0.2 -container-p
12
13  Mar 16 11:18:55 vps298933 dockerd[900]: time="2019-03-16T11:18:55.564648939+06:00" level=info msg="Default bridge (docker0
14  Mar 16 11:18:55 vps298933 dockerd[900]: time="2019-03-16T11:18:55.652024810+06:00" level=info msg="Loading containers: don
15  Mar 16 11:18:56 vps298933 dockerd[900]: time="2019-03-16T11:18:56.070100870+06:00" level=info msg="Docker daemon" commit=7
16  Mar 16 11:18:56 vps298933 dockerd[900]: time="2019-03-16T11:18:56.087081485+06:00" level=info msg="Daemon has completed in
17  Mar 16 11:18:56 vps298933 systemd[1]: Started Docker Application Container Engine.
18  Mar 16 11:18:56 vps298933 dockerd[900]: time="2019-03-16T11:18:56.126780847+06:00" level=info msg="API listen on /var/run/
19  Mar 16 12:35:13 vps298933 dockerd[900]: time="2019-03-16T12:35:13.895938839+06:00" level=error msg="stream copy error: rea
20  Mar 16 12:35:13 vps298933 dockerd[900]: time="2019-03-16T12:35:13.968707954+06:00" level=error msg="Error running exec 01d
21  Mar 16 12:35:21 vps298933 dockerd[900]: time="2019-03-16T12:35:21.967738507+06:00" level=error msg="stream copy error: rea
22  Mar 16 12:35:22 vps298933 dockerd[900]: time="2019-03-16T12:35:22.035983646+06:00" level=error msg="Error running exec 804

    Note

    You might need to press Ctrl+C or :q to end the status command if it did not return you back to your prompt.

Verify Docker Install

  1. View the version of Docker. You should see a similar version.

    docker --version

    1 root@vps298933:~# docker --version
2 Docker version 19.03.5, build 633a0ea838

  2. View the available options using the --help command

    docker --help

     1 root@vps298933:~# docker --help
 2
 3 Usage:  docker [OPTIONS] COMMAND
 4
 5 A self-sufficient runtime for containers
 6
 7 Options:
 8     --config string      Location of client config files (default "/root/.docker")
 9 -D, --debug              Enable debug mode
10 -H, --host list          Daemon socket(s) to connect to
11 -l, --log-level string   Set the logging level ("debug"|"info"|"warn"|"error"|"fatal") (default "info")
12     --tls                Use TLS; implied by --tlsverify
13     --tlscacert string   Trust certs signed only by this CA (default "/root/.docker/ca.pem")
14     --tlscert string     Path to TLS certificate file (default "/root/.docker/cert.pem")
15     --tlskey string      Path to TLS key file (default "/root/.docker/key.pem")
16     --tlsverify          Use TLS and verify the remote
17 -v, --version            Print version information and quit
18
19 Management Commands:
20 config      Manage Docker configs
21 container   Manage containers
22 image       Manage images
23 network     Manage networks
24 node        Manage Swarm nodes
25 plugin      Manage plugins
26 secret      Manage Docker secrets
27 service     Manage services
28 stack       Manage Docker stacks
29 swarm       Manage Swarm
30 system      Manage Docker
31 trust       Manage trust on Docker images
32 volume      Manage volumes
33
34 Commands:
35
36 attach      Attach local standard input, output, and error streams to a running container
37 build       Build an image from a Dockerfile
38 commit      Create a new image from a container’s changes
39 cp          Copy files/folders between a container and the local filesystem
40 create      Create a new container
41 diff        Inspect changes to files or directories on a container’s filesystem
42 events      Get real time events from the server
43 exec        Run a command in a running container
44 export      Export a container’s filesystem as a tar archive
45 history     Show the history of an image
46 images      List images
47 import      Import the contents from a tarball to create a filesystem image
48 info        Display system-wide information
49 inspect     Return low-level information on Docker objects
50 kill        Kill one or more running containers
51 load        Load an image from a tar archive or STDIN
52 login       Log in to a Docker registry
53 logout      Log out from a Docker registry
54 logs        Fetch the logs of a container
55 pause       Pause all processes within one or more containers
56 port        List port mappings or a specific mapping for the container
57 ps          List containers
58 pull        Pull an image or a repository from a registry
59 push        Push an image or a repository to a registry
60 rename      Rename a container
61 restart     Restart one or more containers
62 rm          Remove one or more containers
63 rmi         Remove one or more images
64 run         Run a command in a new container
65 save        Save one or more images to a tar archive (streamed to STDOUT by default)
66 search      Search the Docker Hub for images
67 start       Start one or more stopped containers
68 stats       Display a live stream of container(s) resource usage statistics
69 stop        Stop one or more running containers
70 tag         Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE
71 top         Display the running processes of a container
72 unpause     Unpause all processes within one or more containers
73 update      Update configuration of one or more containers
74 version     Show the Docker version information
75 wait        Block until one or more containers stop, then print their exit codes

  3. View the docker system information

    sudo docker info

     1 root@vps298933:~# docker info
 2 Containers: 0
 3 Running: 0
 4 Paused: 0
 5 Stopped: 0
 6 Images: 0
 7 Server Version: 18.06.1-ce
 8 Storage Driver: overlay2
 9 Backing Filesystem: extfs
10 Supports d_type: true
11 Native Overlay Diff: true
12 Logging Driver: json-file
13 Cgroup Driver: cgroupfs
14 Plugins:
15 Volume: local
16 Network: bridge host macvlan null overlay
17 Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
18 Swarm: inactive
19 Runtimes: runc
20 Default Runtime: runc
21 Init Binary: docker-init
22 containerd version:  (expected: 468a545b9edcd5932818eb9de8e72413e616e86e)
23 runc version: N/A (expected: 69663f0bd4b60df09991c08812a60108003fa340)
24 init version: v0.18.0 (expected: fec3683b971d9c3ef73f284f176672c44b448662)
25 Security Options:
26 apparmor
27 seccomp
28 Profile: default
29 Kernel Version: 4.15.0-43-generic
30 Operating System: Ubuntu 18.04.1 LTS
31 OSType: linux
32 Architecture: x86_64
33 CPUs: 1
34 Total Memory: 3.759GiB
35 Name: vps298933
36 ID: H2AG:BHBS:OKEZ:UJZ7:S2JB:MXP5:WYKU:42BD:SEOK:VDBS:2VTH:MTTA
37 Docker Root Dir: /var/lib/docker
38 Debug Mode (client): false
39 Debug Mode (server): false
40 Registry: https://index.docker.io/v1/
41 Labels:
42 Experimental: false
43 Insecure Registries:
44 127.0.0.0/8
45 Live Restore Enabled: false
46
47 WARNING: No swap limit support

  4. Verify the hello-world container runs

    sudo docker run hello-world

     1 root@vps298933:~# docker run hello-world
 2 Unable to find image 'hello-world:latest' locally
 3 latest: Pulling from library/hello-world
 4 1b930d010525: Pull complete
 5 Digest: sha256:2557e3c07ed1e38f26e389462d03ed943586f744621577a99efb77324b0fe535
 6 Status: Downloaded newer image for hello-world:latest
 7
 8 Hello from Docker!
 9 This message shows that your installation appears to be working correctly.
10
11 To generate this message, Docker took the following steps:
12 1. The Docker client contacted the Docker daemon.
13 2. The Docker daemon pulled the "hello-world" image from the Docker Hub. (amd64)
14 3. The Docker daemon created a new container from that image which runs the executable that produces the output you are currently reading.
15 4. The Docker daemon streamed that output to the Docker client, which sent it to your terminal.
16
17 To try something more ambitious, you can run an Ubuntu container with:
18 $ docker run -it ubuntu bash
19
20 Share images, automate workflows, and more with a free Docker ID:
21 https://hub.docker.com/
22
23 For more examples and ideas, visit:
24 https://docs.docker.com/get-started/

  5. View the docker images. You should see the hello-world image under the REPOSITORY column.

    sudo docker images

    1 root@vps298933:~# sudo docker images
2 REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
3 hello-world         latest              fce289e99eb9        2 weeks ago         1.84kB

  6. View the active containers (stopped or running)

    • docker ps shows the active containers

    • docker ps -a shows the active (running) and inactive (stopped) containers

    Note

    Some containers stay running in the background (daemon mode). Others operate as a process. They start, process some data, and then exit.

    sudo docker ps

    Notice that there are no running containers.

    1 root@vps298933:~# docker ps
2 CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES

    sudo docker ps -a

    Notice that the container has exited.

    1 root@vps298933:~# sudo docker ps -a
2 CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                  PORTS               NAMES
3 67a9ee91dbfc        hello-world         "/hello"            6 days ago          Exited (0) 6 days ago                       nervous_dijkstra
4 root@vps298933:~#

Running Docker as non-root

If your VPS does not have a root login or you prefer to use a user account, you can configure Docker to run without out using sudo.

  1. Find your username using whoami

    whoami

  2. Add your user to docker group.

    sudo groupadd docker
sudo usermod -aG docker username
sudo newgrp docker