Docker - Index of commands

mail

docker rmi

Usage

Remove one or more images
You can specify the image to delete with : It's also possible to provide docker rmi with a list of images to delete :
docker rmi $([command that returns the list of images to delete])

Example

Delete an image by ID

  1. docker image ls
    REPOSITORY		TAG		IMAGE ID		CREATED			SIZE
debian			bookworm	0ce03c8a15ec		8 hours ago		117MB
alpine			3.16		8471affe5de5		7 months ago		5.55MB
  2. docker rmi 0ce03c8a15ec
    Untagged: debian:bookworm
Untagged: debian@sha256:133a1f2aa9e55d1c93d0ae1aaa7b94fb141265d0ee3ea677175cdb96f5f990e5
Deleted: sha256:0ce03c8a15ec97f121b394857119e3e7652bba5a66845cbfa449d87a5251914e
Deleted: sha256:7cea17427f83f6c4706c74f94fb6d7925b06ea9a0701234f1a9d43f6af11432a

Delete untagged images

docker rmi $(docker images -f "dangling=true" -q)
mail

docker rm

Usage

Remove one or more containers
  1. When trying to delete an image :
    docker rmi 0ce03c8a15ec
    Error response from daemon: conflict: unable to delete 0ce03c8a15ec (must be forced) - image is being used by stopped container 2cb71c235c6a
  2. Get information about that stopped container still holding the image I want to delete :
    docker ps -a
    CONTAINER ID	IMAGE		COMMAND		CREATED			STATUS				PORTS		NAMES
2cb71c235c6a	0ce03c8a15ec	"bash"		8 minutes ago		Exited (130) About a minute ago			test
  3. Remove that container :
    docker rm 2cb71c235c6a
    2cb71c235c6a
  4. Check :
    docker ps -a
    (gone)
  5. Now I can delete the image.
mail

docker images

Usage

List + filter images

Flags

Flag Usage
-f
--filter "key=value" 		filter output based on condition(s) provided
-q --quiet return image IDs only

Example

List the most recently created images

docker images

List untagged images (source)

When a new version on an existing image is built, the repo:tag moves to the new image. The previous version of the image is left untagged (aka "dangling") with <none>:<none>.
docker images --filter "dangling=true"

List images by name

  1. Let's consider we have :
    docker images
    REPOSITORY			TAG			IMAGE ID		CREATED			SIZE
foobar			2.14.13			8d184a936572		17 hours ago		283MB
foobar			2.14.12			e116aecf034c		17 hours ago		283MB
foobar			2.15.0			ee657cd3af27		17 hours ago		283MB
foobar			2.16.2			5a9fb562f34b		25 hours ago		284MB
debian				bookworm-slim		971072c49252		13 days ago		74.8MB
debian				bookworm		0ce03c8a15ec		2 months ago		117MB
vmware/powerclicore		latest			9359cebc65e4		8 months ago		2.15GB
alpine				3.16			8471affe5de5		10 months ago		5.55MB
rockylinux			9.1			ce99dcf19c24		13 months ago		176MB
alpine				3.15			c4fc93816858		17 months ago		5.59MB
vmware/powerclicore		12.7			d2d244ad5d73		18 months ago		932MB
nginx				1.19.9-alpine		bfad9487e175		2 years ago		22.6MB
  2. We can list all the foobar images with :
    docker images -f "reference=foobar"
    REPOSITORY			TAG			IMAGE ID		CREATED			SIZE
foobar			2.14.13			8d184a936572		17 hours ago		283MB
foobar			2.14.12			e116aecf034c		17 hours ago		283MB
foobar			2.15.0			ee657cd3af27		17 hours ago		283MB
foobar			2.16.2			5a9fb562f34b		25 hours ago		284MB
mail

docker image

Usage

Do something —described by the part— with images
docker image ls
list images
docker image history
show the history of an image, reporting which steps made it grow
docker image history myimage:latest
IMAGE			CREATED			CREATED BY					SIZE
c5ffa610ab8d		About a minute ago	|1 /bin/sh -c 					614MB		this was caused by the last RUN of my Dockerfile
155a3bf504ad		2 minutes ago		|1 /bin/sh -c 					52.9MB
2b54b499613b		2 minutes ago		/bin/sh -c #(nop)  LABEL comment=blah		0B
e9716a3e46f8		2 minutes ago		/bin/sh -c #(nop)  ARG 			0B
0ce03c8a15ec		3 days ago		/bin/sh -c #(nop)  CMD ["bash"]			0B
<missing>		3 days ago		/bin/sh -c #(nop) ADD file:39d17d2d62…		117MB
mail

docker ps

Usage

List containers

Flags

Flag Usage
-a --all show all containers (default shows just running)
-q --quiet only display container IDs
mail

docker tag

Usage

Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE :
If I get it correctly :
  • an image is named at build time with docker build -t myimage:1.0
  • docker tag adds one more tag / name / alias / ? to the "source image"
mail

docker logs

Usage

Fetch the logs of a container
mail

docker top

Usage

docker top containerId
display the running processes of a container
mail

docker build

Usage

docker build [options] contextPath

Flags

Flag Usage
-f path/to/myDockerfile
--file=path/to/myDockerfile
  • build image from path/to/myDockerfile
  • defaults to contextPath/Dockerfile
--rm Remove intermediate containers after a successful build
-t repo:tag
--tag repo:tag		 Name and tag the resulting image in the repo:tag format
mail

docker container run

Usage

Run a command in a new container
docker container run is equivalent to docker run (source) :
  • both exist for historical reasons :
    • only docker run existed initially
    • docker container run was added later to have more intuitive commands like docker command subcommand since the number of commands was increasing
  • use docker container run, which is the modern way of running a container

Flags

Flag corresponding Dockerfile directive Usage
-d --detach
  • start container in detached mode
  • the container will exit when the root process used to run the container exits
In foreground mode (opposite of detached mode evoked above), docker run can start the process in the container and attach the console to the process's standard input, output, and standard error. It can even pretend to be a TTY (this is what most command line executables expect) and pass along signals. All of that is configurable with -i, -t
--entrypoint=someCommand Overwrite the default entrypoint set by the image with someCommand
-i --interactive interactive mode : keep STDIN open even if not attached
--name myContainer assign a name to the container
-P --publish-all Publish all EXPOSEd ports to the host interfaces. Docker binds each EXPOSEd port to a random port on the host.
-p=portSpecification Publish a container's port/range of ports to the host. This allows mapping ports : hostPort:containerPort
Many syntaxes available, please
--rm (1, 2) when the container exits, remove :
-t Allocate a pseudo-tty
--user userSpecification USER username or UID, with userSpecification : name|uid[:group|gid]
-v volumeSpecification
--volume=volumeSpecification		 VOLUME bind mount a volume using volumeSpecification : X:Y:Z
  • X can either be :
    • a host directory, specified as an absolute path
    • an arbitrary volume name
    • omitted (aka anonymous volume). In such case, it will be created automatically with a path + name like : /var/lib/docker/volumes/848acf58ffb933b/
  • Y is :
    • the path to the volume inside the container (aka mount point)
    • specified as an absolute path
  • Z :
    • is for permissions : rw, ro,
    • can be omitted. No idea what it defaults to
It is possible to declare a volume in a Dockerfile with the VOLUME directive, with the limitation of not being able to specify a host directory.
  • This is because an image has no control on its environment and can not guarantee that the host directory actually exists.
  • If you want to control both ends of a volume specification, you have no choice but use the -v / --volume flag.
-w dir --workdir dir WORKDIR use dir as working directory inside the container
mail

docker inspect

Usage

Return low-level information on Docker objects

Flags

Flag Usage
-f formatString
--format=formatString		 Format the output using the given Go template (details : 1, 2)
  • By default, data is returned as a JSON array.
  • formatString is not just a list of output format flags (as seen with other tools) but rather a mix of :
    • the list of queried fields
    • and a function (if any) to combine them to build the result
    like in the pseudo-code : join(', ', (field1, field2, field3))

Example

Let's discover docker inspect :

  • Learn everything about the containerId container :
    docker inspect containerId
  • Extract specific values, considering this "inspection" result : 
    [
	{
		"Id": "sha256:4000f524b3ffb2282cd02892b8f89ec886bda2f71d87096f14378a6043ef4fab",
		
		"DockerVersion": "18.03.1-ce",
		"Config": {
			
			"Hostname": "",
			"Env": [
				"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
    • docker inspect containerId -f '{{.DockerVersion}}'
      18.03.1-ce
    • docker inspect containerId -f {{.Config.Env}}
      [PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin]
  • Values only or keys + values :
    docker inspect -f '{{.State}}' containerId
    {running true false false false false 5654 0  2020-09-09T09:49:07.578164883Z 0001-01-01T00:00:00Z <nil>}
    docker inspect -f '{{json .State}}' containerId
    {"Status":"running", "Running":true, "Paused":false, "Restarting":false, "OOMKilled":false, "Dead":false, "Pid":5654, "ExitCode":0, "Error":"", "StartedAt":"2020-09-09T09:49:07.578164883Z", "FinishedAt":"0001-01-01T00:00:00Z"}

Output formatting hacks :

jq :

Some experienced users prefer jq as an alternative to --format.

Python :

And if jq is not available, Python comes to the rescue :
  • raw result (JSON array) :
    docker inspect -f '{{.State}}' containerId
    {running true false false false false 5654 0  2020-09-09T09:49:07.578164883Z 0001-01-01T00:00:00Z <nil>}
  • keys + values as a JSON string :
    docker inspect -f '{{json .State}}' containerId
    {"Status":"running", "Running":true, "Paused":false, "Restarting":false, "OOMKilled":false, "Dead":false, "Pid":5654, "ExitCode":0, "Error":"", "StartedAt":"2020-09-09T09:49:07.578164883Z", "FinishedAt":"0001-01-01T00:00:00Z"}
  • pretty print of data (with keys sorted alphabetically) :
    docker inspect -f '{{json .State}}' containerId | python -m json.tool
    {
	"Dead": false,
	"Error": "",
	"ExitCode": 0,
	"FinishedAt": "0001-01-01T00:00:00Z",
	"OOMKilled": false,
	"Paused": false,
	"Pid": 5654,
	"Restarting": false,
	"Running": true,
	"StartedAt": "2020-09-09T09:49:07.578164883Z",
	"Status": "running"
}
mail

docker exec

Usage

Run a command in a running container

Flags

Flag Usage
-i --interactive Keep STDIN open even if not attached
-t --tty Allocate a pseudo-TTY
-u --user specify a username or UID

Example

Run a command in a container as a specific user :

  • docker exec -u bob -it 9f78e57b54d9 whoami
    bob
  • Open a shell as bob (details) :
    docker exec -u bob -it 9f78e57b54d9 sh