Docker Swarm

Note: Use sudo if your user is not in the docker group.

Docker ps Command

• List all the running containers in the VM/VPC

Command Syntax

docker ps

Sample Output

CONTAINER ID   IMAGE          COMMAND                  CREATED         STATUS         PORTS                    NAMES
a1b2c3d4e5f6   ubuntu         "/bin/bash"              3 minutes ago     Up 3 minutes                              mycontainer
b7c8d9e0f1g2   nginx:latest   "/docker-entrypoint.…"   2 minutes ago     Up 2 minutes     0.0.0.0:80->80/tcp       webserver

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Docker exec Command

• The command docker exec is used to access a running Docker container’s shell or run the command inside the container from the VM/VPC.

Prerequisite Need docker ps command to get the container ID

Command Syntax

docker exec <options> <container_name_or_id> <command>

Options

Options	Description
-d, --detach	Detached mode: run command in the background
-i, --interactive	Keep STDIN open for interaction
-t, --tty	Allocate a pseudo-TTY (Pseudo Terminal)
-w, --workdir	Working directory inside the container

Common Patterns or Use Cases

1) With container name

docker exec -it mycontainer bash

Sample Output

// Opens a Shell for interactive mode
root@ca1b2c3d4e5f6:/#

2) With container id

docker exec -it a1b2c3d4e5f6 bash

Sample Output

root@a1b2c3d4e5f6:/#

3) With detach flag

docker exec -d mycontainer mkdir test

Sample Output

// The detached mode causes the command to run in the background only show the commad id in the terminal
c3f279d17e0a1d2be0f85eaf41f905f6bda76b223f214d4b73f6e8ed4a7e1d23 // container command id

4) Without flag

docker exec mycontainer ls

Sample Output

// list the folder from the working directory
bin   boot  dev  etc  home  lib  lib64  media  mnt  opt  proc
root  run   sbin srv  sys   test  tmp  usr  var

5) With workdir flag

docker exec -it -w /root mycontainer pwd

Sample Output

/root

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Docker restart command

• Restart the Container with same configuration.

Prerequisite Need docker ps command to get the container ID

Command Syntax

docker restart a1b2c3d4e5f6

Sample Output

a1b2c3d4e5f6

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Docker build Command

• Build a docker image from the Dockerfile.

Prerequisite

• Need a Dockerfile

Command Syntax

docker build -t <image_name> -f <PATH/TO/Dockerfile> .

Options

Options	Description
-t, --tag	name of the image
-f, --file	Dockerfile Path
--build-arg	Set build-time arguments
--no-cache	Do not use cache when building the image

Common Patterns or Use Cases

1) Dockerfile in the working directory

docker build -t myimage:latest .

Sample Output

[+] Building 12.3s (5/7) FINISHED
 => [internal] load build definition from Dockerfile                                                                                      0.0s
 => => transferring dockerfile: 123B                                                                                                     0.0s
 => [internal] load .dockerignore                                                                                                         0.0s
 => => transferring context: 2B                                                                                                           0.0s
 => [internal] load metadata for docker.io/library/alpine:latest                                                                          1.2s
 => [1/3] FROM docker.io/library/alpine:latest                                                                                            1.0s
 => [2/3] RUN apk add --no-cache curl                                                                                                    9.5s
 => [3/3] CMD ["sh"]                                                                                                                      0.2s

2) Dockerfile not in the working directory

docker build -t myimage:latest -f ./docker/Dockerfile .

Sample Output

[+] Building 2.3s (7/7) FINISHED
 => [internal] load build definition from Dockerfile                                                                                      0.0s
 => => transferring dockerfile: 123B                                                                                                     0.0s
 => [internal] load .dockerignore                                                                                                         0.0s
 => => transferring context: 2B                                                                                                           0.0s
 => [internal] load metadata for docker.io/library/alpine:latest                                                                          0.5s
 => [1/4] FROM docker.io/library/alpine:latest                                                                                            0.4s
 => [2/4] RUN apk add --no-cache curl                                                                                                    0.0s
 => CACHED [3/4] COPY . /app                                                                                                              0.0s
 => CACHED [4/4] CMD ["sh"]                                                                                                               0.0s

3) With no cache flag

docker build --no-cache -t myimage:latest .

Sample Output

[+] Building 12.5s (7/7) FINISHED
 => [internal] load build definition from Dockerfile                                                                                      0.0s
 => => transferring dockerfile: 123B                                                                                                     0.0s
 => [internal] load .dockerignore                                                                                                         0.0s
 => => transferring context: 2B                                                                                                           0.0s
 => [internal] load metadata for docker.io/library/alpine:latest                                                                          1.2s
 => [1/4] FROM docker.io/library/alpine:latest                                                                                            1.1s
 => [2/4] RUN apk add --no-cache curl                                                                                                    9.8s
 => [3/4] COPY . /app                                                                                                                      0.3s
 => [4/4] CMD ["sh"]                                                                                                                      0.1s

4) Passing arguments during build

docker build --build-arg VERSION=3.18 -t myimage:latest .

Sample Output

[+] Building 7.8s (6/6) FINISHED
 => [internal] load build definition from Dockerfile                                                                                      0.0s
 => => transferring dockerfile: 123B                                                                                                     0.0s
 => [internal] load .dockerignore                                                                                                         0.0s
 => => transferring context: 2B                                                                                                           0.0s
 => [internal] load metadata for docker.io/library/alpine:3.18                                                                           1.2s
 => [1/4] FROM docker.io/library/alpine:3.18                                                                                             1.0s
 => [2/4] RUN apk add --no-cache curl                                                                                                    6.2s
 => [3/4] CMD ["sh"]                                                                                                                      0.2s

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Docker cp Command

• Copy the content from source path to target path
• Can Copy from VM file system to Container and Vice-versa.

Prerequisite Need docker ps command to get the container ID

Command Syntax

1) From VM to container

docker cp ./some_file <container_id>:/path/to/dump

Example

docker cp ./test.txt a1b2c3d4e5f6:/mnt

1) From container to VM

docker cp <container_id>:/path/to/some_file ./path/to/dump

Example

docker cp a1b2c3d4e5f6:/etc/hostname ./dump/

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Docker logs Command

• Show the logs of a container

Prerequisite Need docker ps command to get the container ID

Command Syntax

docker logs <container_id>

Example

docker logs a1b2c3d4e5f6

Sample Output

[INFO] Starting web server on port 8080...
[INFO] Server listening at http://0.0.0.0:8080
[WARN] Cache not found, starting with empty cache.

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Docker stats Command

• This command give the real-time metrics for the container’s CPU and memory usage.

Prerequisite Need docker ps command to get the container ID

Command Syntax

docker stats <container_name_or_id>

Example

docker stats a1b2c3d4e5f6

Sample Output

CONTAINER ID   NAME         CPU %     MEM USAGE / LIMIT     MEM %     NET I/O           BLOCK I/O         PIDS
a1b2c3d4e5f6   mycontainer  0.45%     12.34MiB / 512MiB      2.41%     1.2kB / 1.5kB      0B / 0B           1

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Docker prune Command

• Remove all unused containers, networks, images.
• By default volumes are not remove because to prevent data loss

Command Syntax

docker system prune <option>

Options

Options	Description
-a, --all	Remove unused and dangling images
--volumes	Remove unused volumes

Use Cases

1) Default

docker system prune

Sample Output

WARNING! This will remove:
  - all stopped containers
  - all networks not used by at least one container
  - all dangling images
  - all build cache

Are you sure you want to continue? [y/N] y

Deleted Containers:
a1b2c3d4e5f6
b7c8d9e0f1g2

Deleted Networks:
mycontainer_network

Deleted Images:
untagged: myimage:latest
deleted: sha256:123abc456def...

Deleted build cache:
Total reclaimed space: 305.6MB

2) Use volume flag to remove unused volume

docker system prune --volumes

Sample Output

WARNING! This will remove:
  - all stopped containers
  - all networks not used by at least one container
  - all dangling images
  - all build cache
  - all unused volumes

Are you sure you want to continue? [y/N] y

Deleted Containers:
c3d4e5f6g7h8
d9e0f1g2h3i4

Deleted Networks:
myapp_default

Deleted Volumes:
myapp_volume
mycontainer_volume

Deleted Images:
untagged: myapp:old
deleted: sha256:abc123...

Deleted build cache:
Total reclaimed space: 457.2MB

3) With all flag

docker system prune -a

Sample Output

WARNING! This will remove:
  - all stopped containers
  - all networks not used by at least one container
  - all images without at least one container associated to them
  - all build cache

Are you sure you want to continue? [y/N] y

Deleted Containers:
e3f1a2c4b6d8
f5d9a0c1b2e3

Deleted Networks:
myapp_network

Deleted Images:
untagged: node:alpine
deleted: sha256:abc123...
untagged: myapp:old
deleted: sha256:def456...

Deleted build cache:
Total reclaimed space: 692.4MB

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Docker inspect Command

• Display detailed information the containers in JSON format

Prerequisite Need docker ps command to get the container ID

Command Syntax

docker container inspect <container_id>

Options

Options	Description
-f, --format	Filter or format output using Go templating

Use Cases 1) Without flag

docker container inspect a1b2c3d4e5f6

Sample Output

[
  {
    "Id": "a1b2c3d4e5f6g7h8i9j0",
    "Created": "2025-05-27T12:34:56.789Z",
    "Path": "/bin/bash",
    "Args": [],
    "State": {
      "Status": "running",
      "Running": true,
      "StartedAt": "2025-05-27T12:35:01.000Z"
    },
    "Image": "sha256:123abc...",
    "Name": "/mycontainer",
    "HostConfig": {
      "NetworkMode": "default"
    },
    "Mounts": [
      {
        "Type": "volume",
        "Name": "my-volume",
        "Destination": "/data"
      }
    ],
    "Config": {
      "Hostname": "a1b2c3d4e5f6",
      "Image": "ubuntu",
      "Cmd": [
        "/bin/bash"
      ]
    },
    "NetworkSettings": {
      "IPAddress": "172.17.0.2"
    }
  }
]

2) With flag

docker container inspect --format '{{ .NetworkSettings.IPAddress }}' a1b2c3d4e5f6

Sample Output

172.17.0.2

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Command for start/stop/restart/status for Docker Daemon in Ubuntu

• status -> Shows Docker’s status
• start -> Starts Docker Engine
• stop -> Halts Docker Engine and all containers
• restart -> Restarts the Docker daemon cleanly.

Command Syntax 1) To check the status of the docker engine

systemctl status docker

Sample Output

● docker.service - Docker Application Container Engine
     Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2025-05-28 09:32:44 UTC; 2min ago
TriggeredBy: ● docker.socket
       Docs: https://docs.docker.com
   Main PID: 1135 (dockerd)
      Tasks: 19
     Memory: 48.3M
        CPU: 2.134s
     CGroup: /system.slice/docker.service
             └─1135 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

2) To start the docker engine

systemctl start docker

3) To stop the docker engine

systemctl stop docker

4) To restart the docker engine

systemctl restart docker

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