WORKDIR instruction for directory in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the WORKDIR instruction do in a Dockerfile?

WORKDIR sets the working directory for any RUN, CMD, ENTRYPOINT, COPY, and ADD instructions that follow it in the Dockerfile. It changes the current directory inside the container.

beginner

If the directory specified in WORKDIR does not exist, what happens?

Docker will create the directory automatically before setting it as the working directory.

intermediate

How does WORKDIR affect the path for subsequent instructions in a Dockerfile?

After setting WORKDIR, all relative paths in following instructions are based on this directory, making file operations easier and clearer.

intermediate

Can you use multiple WORKDIR instructions in a Dockerfile? What happens?

Yes, you can use multiple WORKDIR instructions. Each one changes the working directory from the previous one. If a relative path is given, it is relative to the current WORKDIR.

intermediate

Example: What is the working directory after these instructions? WORKDIR /app WORKDIR logs

The final working directory is /app/logs because the second WORKDIR 'logs' is relative to the first '/app'.

What does the WORKDIR instruction do in a Dockerfile?

A Exposes a port for the container

B Copies files into the container

C Sets the working directory for following instructions

D Runs a command inside the container

WORKDIR sets the directory where commands run inside the container.

If the directory in WORKDIR does not exist, what does Docker do?

A Throws an error and stops building

B Uses the root directory instead

C Ignores the instruction

D Creates the directory automatically

Docker creates the directory if it does not exist.

What is the working directory after these instructions? WORKDIR /usr WORKDIR local

A /usr/local

B /local

C /usr

D /

The second WORKDIR is relative, so it becomes /usr/local.

Can you use multiple WORKDIR instructions in one Dockerfile?

A No, only one WORKDIR is allowed

B Yes, each changes the working directory

C Yes, but only the first one works

D No, it causes a build error

Multiple WORKDIR instructions are allowed and update the directory.

Which instruction uses the current WORKDIR as base for relative paths?

A All of the above

B RUN

C WORKDIR

D COPY

All these instructions use the current WORKDIR for relative paths.

Explain what the WORKDIR instruction does and why it is useful in a Dockerfile.

Think about how commands run inside the container.

Describe what happens when you use multiple WORKDIR instructions with relative paths in a Dockerfile.

Consider how paths combine step by step.

Practice

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

easy

A. Runs a command when the container starts

B. Deletes files in the container

C. Sets the working directory for commands inside the container

D. Specifies the base image for the container

Solution

1. Step 1: Understand the purpose of WORKDIR

   The WORKDIR instruction sets the folder where subsequent commands run inside the container.

2. Step 2: Compare with other options

   Options A, B, and C describe other Dockerfile instructions or actions, not WORKDIR.

3. Final Answer:

   Sets the working directory for commands inside the container -> Option C

4. Quick Check:

   WORKDIR sets folder for commands [OK]

Hint: WORKDIR sets folder for commands inside container [OK]

Common Mistakes:

• Confusing WORKDIR with CMD or ENTRYPOINT
• Thinking WORKDIR deletes files
• Assuming WORKDIR sets base image

2. Which of the following is the correct syntax to set the working directory to /app in a Dockerfile?

easy

A. WORKDIR /app

B. WORKDIR: /app

C. WORKDIR = /app

D. WORKDIR(/app)

Solution

1. Step 1: Recall Dockerfile syntax for WORKDIR

   The correct syntax is WORKDIR /path without any symbols like colon, equals, or parentheses.

2. Step 2: Check each option

   Options A, B, and D use invalid syntax for Dockerfile instructions.

3. Final Answer:

   WORKDIR /app -> Option A

4. Quick Check:

   WORKDIR uses space, no symbols [OK]

Hint: WORKDIR uses space before path, no symbols [OK]

Common Mistakes:

• Adding colon or equals sign after WORKDIR
• Using parentheses around path
• Forgetting the space between WORKDIR and path

3. Given this Dockerfile snippet:

FROM alpine
WORKDIR /app
RUN touch file.txt
WORKDIR /app/data
RUN echo "hello" > message.txt

Where will the file message.txt be created inside the container?

medium

A. /app/data/file.txt

B. /app/message.txt

C. /message.txt

D. /app/data/message.txt

Solution

1. Step 1: Follow WORKDIR changes

   The first WORKDIR sets directory to /app. The second WORKDIR changes it to /app/data.

2. Step 2: Locate where message.txt is created

   The command RUN echo "hello" > message.txt runs in /app/data, so the file is created there.

3. Final Answer:

   /app/data/message.txt -> Option D

4. Quick Check:

   Last WORKDIR sets folder for commands [OK]

Hint: Last WORKDIR sets current folder for commands [OK]

Common Mistakes:

• Assuming files created in first WORKDIR folder
• Confusing file paths with root directory
• Ignoring multiple WORKDIR instructions

4. You wrote this Dockerfile snippet:

WORKDIR /app
RUN ls
WORKDIR app/data
RUN ls

Why does the second WORKDIR cause an unexpected result?

medium

A. Because WORKDIR cannot be used twice

B. Because relative path 'app/data' resolves to /app/app/data instead of /app/data

C. Because RUN ls is invalid syntax

D. Because /app directory is not created automatically

Solution

1. Step 1: Understand relative paths in WORKDIR

   The second WORKDIR uses a relative path app/data, which is relative to the current directory /app. So it tries to set /app/app/data.

2. Step 2: Understand relative path resolution

   Docker creates /app/app/data automatically if needed, but this nested path is usually unintended if /app/data was desired.

3. Step 3: Identify actual issue

   Relative path app/data is a mistake; use data or absolute /app/data instead.

4. Final Answer:

   Because relative path 'app/data' resolves to /app/app/data instead of /app/data -> Option B

5. Quick Check:

   Relative WORKDIR paths resolve from current dir [OK]

Hint: Relative WORKDIR paths are inside current folder [OK]

Common Mistakes:

• Thinking WORKDIR cannot be used multiple times
• Assuming RUN ls is invalid
• Believing /app is not auto-created

5. You want to create a Dockerfile that:
- Sets working directory to /app
- Creates a subfolder logs
- Changes working directory to logs
- Creates a file app.log

Which Dockerfile snippet correctly does this?

hard

A. WORKDIR /app
RUN mkdir logs
WORKDIR logs
RUN touch app.log

B. WORKDIR /app/logs
RUN mkdir logs
WORKDIR /app
RUN touch app.log

C. RUN mkdir /app/logs
WORKDIR /app/logs
RUN touch app.log

D. WORKDIR /app
RUN touch app.log
WORKDIR logs
RUN mkdir logs

Solution

1. Step 1: Set working directory to /app and create logs folder

   WORKDIR /app RUN mkdir logs WORKDIR logs RUN touch app.log sets WORKDIR to /app and runs mkdir logs to create the subfolder.

2. Step 2: Change WORKDIR to logs and create app.log

   Then it changes WORKDIR to logs (relative to /app) and creates app.log inside it.

3. Step 3: Verify other options

   WORKDIR /app/logs RUN mkdir logs WORKDIR /app RUN touch app.log sets WORKDIR incorrectly and creates logs folder in wrong place. RUN mkdir /app/logs WORKDIR /app/logs RUN touch app.log creates logs folder but misses initial WORKDIR. WORKDIR /app RUN touch app.log WORKDIR logs RUN mkdir logs creates app.log before logs folder and changes WORKDIR before folder exists.

4. Final Answer:

   WORKDIR /app RUN mkdir logs WORKDIR logs RUN touch app.log -> Option A

5. Quick Check:

   Create folder before changing WORKDIR [OK]

Hint: Create folder before changing WORKDIR into it [OK]

Common Mistakes:

• Changing WORKDIR before folder exists
• Creating files in wrong directory
• Using absolute path incorrectly