Viewing container logs in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to view logs of a container named 'webapp'.

Docker

docker logs [1]

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

Awebapp

Brun

Cstart

Dbuild

Attempts:

3 left

💡 Hint

Common Mistakes

Using commands like 'run' or 'start' instead of the container name.

Forgetting to specify the container name.

The docker logs command followed by the container name shows the logs of that container.

2fill in blank

medium

Complete the command to follow the logs of a container named 'dbserver' in real-time.

Docker

docker logs [1] dbserver

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

A-f

Brun

C--tail

D--help

Attempts:

3 left

💡 Hint

Common Mistakes

Using '--tail' instead of '-f' to follow logs.

Using 'run' which starts a container instead of viewing logs.

The -f option makes docker logs follow the log output in real-time.

3fill in blank

hard

Fix the error in the command to show the last 50 lines of logs for container 'api'.

Docker

docker logs --tail=[1] api

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

A100

Bnone

Call

D50

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'all' or 'none' which are invalid values for --tail.

Using a number other than 50 when the question asks for 50 lines.

The --tail option expects a number indicating how many lines to show. Here, 50 is correct.

4fill in blank

hard

Fill both blanks to limit logs to last 20 lines and follow new logs for container 'cache'.

Docker

docker logs [1] 20 [2] cache

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

A--tail

B-f

C--follow

D--since

Attempts:

3 left

💡 Hint

Common Mistakes

Using --since instead of -f to follow logs.

Mixing up the order of options.

Use --tail 20 to show last 20 lines and -f to follow logs live.

5fill in blank

hard

Fill all three blanks to show logs since 10 minutes ago, limit to 100 lines, and follow logs for container 'frontend'.

Docker

docker logs [1] 10m [2] 100 [3] frontend

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

A--since

B--tail

C-f

D--timestamps

Attempts:

3 left

💡 Hint

Common Mistakes

Using --timestamps instead of -f to follow logs.

Mixing up the order of options or missing one.

--since 10m shows logs from last 10 minutes, --tail 100 limits to 100 lines, and -f follows logs live.

Practice

1. What does the command docker logs CONTAINER do?

easy

A. Starts a new container

B. Deletes the specified container

C. Shows the logs of the specified container

D. Lists all running containers

Solution

1. Step 1: Understand the command purpose

   The command docker logs is used to view the output logs of a container.

2. Step 2: Identify the correct action

   Since it shows logs, it helps to see what the container is doing or any errors it has.

3. Final Answer:

   Shows the logs of the specified container -> Option C

4. Quick Check:

   docker logs = show container logs [OK]

Hint: Logs show container output; use docker logs CONTAINER [OK]

Common Mistakes:

• Confusing logs with starting or deleting containers
• Thinking it lists containers instead of showing logs

2. Which of these is the correct syntax to follow live logs of a container named webapp?

easy

A. docker logs webapp -p

B. docker logs -f webapp

C. docker logs --tail webapp

D. docker logs webapp --start

Solution

1. Step 1: Identify the option to follow logs live

   The -f flag means "follow" and shows logs as they appear in real time.

2. Step 2: Check the syntax correctness

   The correct syntax is docker logs -f webapp. Other options are invalid or incorrect.

3. Final Answer:

   docker logs -f webapp -> Option B

4. Quick Check:

   -f means follow logs live [OK]

Hint: Use -f to follow logs live as they update [OK]

Common Mistakes:

• Using --tail without a number to follow logs
• Adding invalid flags like --start or -p
• Placing flags after container name incorrectly

3. What will be the output of the command docker logs --tail 3 mycontainer if the container's last 5 log lines are:

Line1
Line2
Line3
Line4
Line5

medium

A. Line3
Line4
Line5

B. Line1
Line2
Line3

C. Line4
Line5

D. Line1
Line2
Line3
Line4
Line5

Solution

1. Step 1: Understand the --tail option

   The --tail 3 option shows only the last 3 lines of the logs.

2. Step 2: Select the last 3 lines from the given logs

   The last 3 lines are Line3, Line4, and Line5.

3. Final Answer:

   Line3 Line4 Line5 -> Option A

4. Quick Check:

   --tail 3 shows last 3 lines [OK]

Hint: --tail N shows last N lines of logs [OK]

Common Mistakes:

• Choosing first lines instead of last lines
• Confusing --tail with -f
• Expecting all logs instead of limited lines

4. You run docker logs -f myapp but see no output even though the app is running. What is the likely problem?

medium

A. You need to restart Docker daemon

B. The -f flag is not supported

C. Logs are disabled by default

D. The container name is incorrect or not running

Solution

1. Step 1: Check container status and name

   If the container name is wrong or the container is stopped, no logs will appear.

2. Step 2: Understand the -f flag behavior

   The -f flag follows logs live, but if no logs exist or container is not running, output is empty.

3. Final Answer:

   The container name is incorrect or not running -> Option D

4. Quick Check:

   No logs means container name or status issue [OK]

Hint: Check container name and running status first [OK]

Common Mistakes:

• Assuming -f flag is unsupported
• Thinking logs are disabled by default
• Restarting Docker unnecessarily

5. You want to see only the last 10 lines of logs from a container named dbserver and keep watching new logs as they appear. Which command should you use?

hard

A. All of the above

B. docker logs -f --tail 10 dbserver

C. docker logs --tail=10 -f dbserver

D. docker logs --tail 10 -f dbserver

Solution

1. Step 1: Understand combined options usage

   Both -f (follow) and --tail 10 (last 10 lines) can be combined in any order before the container name.

2. Step 2: Check command syntax flexibility

   Docker accepts options in any order before the container name, so all listed commands are valid.

3. Final Answer:

   All of the above -> Option A

4. Quick Check:

   Options order flexible before container name [OK]

Hint: Options order flexible before container name [OK]

Common Mistakes:

• Thinking options must be in fixed order
• Placing options after container name
• Using invalid flags or syntax