RUN instruction for executing commands in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the Dockerfile line to run a command during image build.

Docker

RUN [1]

Drag options to blanks, or click blank then click option'

ACMD python app.py

Bapt-get update

CEXPOSE 80

DCOPY . /app

Attempts:

3 left

💡 Hint

Common Mistakes

Using COPY or CMD with RUN, which are different instructions.

Trying to expose ports with RUN instead of EXPOSE.

The RUN instruction executes commands during the image build. Here, apt-get update updates package lists.

2fill in blank

medium

Complete the RUN command to install curl using apt-get.

Docker

RUN apt-get update && apt-get [1] -y curl

Drag options to blanks, or click blank then click option'

Ainstall

Bremove

Cupgrade

Dclean

Attempts:

3 left

💡 Hint

Common Mistakes

Using remove instead of install.

Using upgrade which updates existing packages but doesn't install new ones.

The install command installs packages. Here, it installs curl after updating package lists.

3fill in blank

hard

Fix the error in the RUN instruction to update and install git.

Docker

RUN apt-get update && apt-get [1] git

Drag options to blanks, or click blank then click option'

A-y install

Binstall

Cinstall -y

D-y remove

Attempts:

3 left

💡 Hint

Common Mistakes

Placing -y after the package name.

Using remove instead of install.

The -y option must come before the package name. Correct syntax is apt-get install -y git.

4fill in blank

hard

Fill both blanks to run a shell command that creates a directory and lists its contents.

Docker

RUN mkdir [1] && ls [2]

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A/app

B/var

D/tmp

Attempts:

3 left

💡 Hint

Common Mistakes

Creating one directory but listing another.

Using invalid directory paths.

The command creates the /app directory and then lists its contents with ls /app.

5fill in blank

hard

Fill all three blanks to run a command that updates, installs vim, and cleans up.

Docker

RUN apt-get [1] && apt-get install [2] vim && apt-get [3]

Drag options to blanks, or click blank then click option'

Aupdate

B-y

Cclean

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using remove instead of clean at the end.

Omitting the -y flag during install.

The command updates package lists, installs vim with automatic yes, and cleans up temporary files.

Practice

1. What does the RUN instruction do in a Dockerfile?

easy

A. Executes commands during the image build process

B. Starts a container from an image

C. Copies files from host to container

D. Defines environment variables for the container

Solution

1. Step 1: Understand Dockerfile instructions

   The RUN instruction is used to execute commands while building the Docker image.

2. Step 2: Differentiate from other instructions

   Other instructions like COPY or ENV serve different purposes, not command execution.

3. Final Answer:

   Executes commands during the image build process -> Option A

4. Quick Check:

   RUN = execute commands during build [OK]

Hint: RUN runs commands while building the image [OK]

Common Mistakes:

• Confusing RUN with CMD or ENTRYPOINT
• Thinking RUN starts containers
• Mixing RUN with COPY or ENV

2. Which of the following is the correct syntax to install curl using RUN in a Debian-based Docker image?

easy

A. RUN apt-get install curl

B. RUN apt-get update && apt-get install -y curl

C. RUN install curl

D. RUN curl install

Solution

1. Step 1: Understand package installation in Debian

   Before installing packages, you must update the package list using apt-get update.

2. Step 2: Use correct flags and chaining

   The -y flag auto-confirms installation, and chaining commands with && ensures update runs before install.

3. Final Answer:

   RUN apt-get update && apt-get install -y curl -> Option B

4. Quick Check:

   Update then install with -y flag [OK]

Hint: Always update before install and use -y flag [OK]

Common Mistakes:

• Skipping apt-get update
• Not using -y to auto-confirm
• Wrong command order or syntax

3. Given this Dockerfile snippet:

FROM ubuntu:latest
RUN echo "Hello" && echo "World"

What will be the output when building this Docker image?

medium

A. Hello World printed during build

B. No output shown during build

C. Error because of missing semicolon

D. Only 'Hello' printed, 'World' ignored

Solution

1. Step 1: Analyze the RUN command chaining

   The command uses && to run two echo commands sequentially during build.

2. Step 2: Understand Docker build output

   During build, the output of RUN commands is shown in the terminal, so both 'Hello' and 'World' will print.

3. Final Answer:

   Hello World printed during build -> Option A

4. Quick Check:

   RUN shows command output during build [OK]

Hint: RUN output appears during build, && runs commands sequentially [OK]

Common Mistakes:

• Thinking RUN output is hidden
• Confusing && with ;
• Assuming only first command runs

4. Identify the error in this Dockerfile RUN instruction:

RUN apt-get update & apt-get install -y git

medium

A. RUN cannot have multiple commands

B. Missing -y flag for apt-get install

C. apt-get update should be last command

D. Using single & instead of && causes syntax error

Solution

1. Step 1: Check command chaining syntax

   Single & runs command in background and is invalid in Docker RUN; && is needed to chain commands properly.

2. Step 2: Confirm correct chaining for sequential execution

   Using && ensures the second command runs only if the first succeeds.

3. Final Answer:

   Using single & instead of && causes syntax error -> Option D

4. Quick Check:

   Use && to chain commands in RUN [OK]

Hint: Use && not & to chain commands in RUN [OK]

Common Mistakes:

• Using & instead of &&
• Ignoring command chaining rules
• Assuming RUN runs commands in parallel

5. You want to reduce Docker image layers by combining multiple commands in a single RUN instruction. Which is the best way to do this?

hard

A. Use multiple RUN instructions, one per command

B. Separate commands with semicolons in multiple RUN lines

C. Chain commands with && inside one RUN instruction

D. Use CMD instead of RUN for multiple commands

Solution

1. Step 1: Understand Docker image layers

   Each RUN instruction creates a new image layer, increasing image size.

2. Step 2: Combine commands to reduce layers

   Chaining commands with && inside one RUN instruction runs them sequentially in a single layer.

3. Final Answer:

   Chain commands with && inside one RUN instruction -> Option C

4. Quick Check:

   Combine commands with && to reduce layers [OK]

Hint: Chain commands with && in one RUN to reduce layers [OK]

Common Mistakes:

• Using multiple RUNs increases layers
• Using CMD instead of RUN for build steps
• Separating commands with semicolons without chaining