Running a container with docker run - Step-by-Step Execution

Process Flow - Running a container with docker run

Start: User types docker run command

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Docker CLI parses command

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Check if image exists locally

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Create container

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Start container process

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Container runs and outputs logs

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Container stops or runs

This flow shows how the docker run command is processed: parsing, image check, container creation, and running.

Execution Sample

Docker

docker run hello-world

Runs the hello-world container which prints a welcome message and then exits.

Process Table

Step	Action	Evaluation	Result
1	User runs 'docker run hello-world'	Command received	Start processing
2	Check if 'hello-world' image exists locally	Image found?	No
3	Pull 'hello-world' image from Docker Hub	Download image layers	Image downloaded
4	Create container from 'hello-world' image	Container created	Container ready
5	Start container process	Run container's default command	Container runs
6	Container outputs welcome message	Prints to terminal	Message displayed
7	Container process ends	Container stops	Container exited
8	docker run command ends	Container stopped	Return to prompt

💡 Container finishes running the hello-world program and exits, ending the docker run command.

Status Tracker

Variable	Start	After Step 3	After Step 5	After Step 7
Image 'hello-world'	Not present	Downloaded	Downloaded	Downloaded
Container state	None	None	Running	Exited
Output	None	None	Welcome message	Welcome message

Key Moments - 2 Insights

Why does docker pull the image even if I just typed docker run?

Because docker run first checks if the image is available locally (see step 2). If not found, it pulls the image (step 3) before creating the container.

Does the container keep running after the hello-world message?

No, the container runs the hello-world program which prints a message and then exits (steps 6 and 7). The container stops immediately after.

Visual Quiz - 3 Questions

Look at the execution table, at which step does Docker download the image?

A Step 3

B Step 2

C Step 5

D Step 6

💡 Hint

Check the 'Action' and 'Result' columns in step 3 for image download details.

According to the variable tracker, what is the container state after step 5?

A Exited

B Running

C None

D Paused

💡 Hint

Look at the 'Container state' row under 'After Step 5' in the variable tracker.

If the image was already present locally, which step would be skipped?

A Step 6

B Step 4

C Step 3

D Step 7

💡 Hint

Step 3 is about pulling the image; if image exists, Docker skips pulling.

Concept Snapshot

docker run <image> : Runs a container from the specified image.
If image not local, Docker pulls it first.
Creates and starts the container.
Container runs its default command.
Output shows in terminal.
Container stops when command ends.

Full Transcript

When you run 'docker run hello-world', Docker first checks if the image is on your computer. If not, it downloads the image from the internet. Then it creates a container from that image and starts it. The container runs the program inside, which prints a welcome message. After the message, the container stops and the command finishes. This process happens step-by-step as shown in the execution table and variable tracker.