kubectl logs for debugging in Kubernetes - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the command kubectl logs <pod-name> do?

It shows the logs (output messages) from the main container inside the specified pod. This helps to see what the application inside the pod is doing or if there are any errors.

beginner

How do you view logs from a specific container in a pod with multiple containers?

Use kubectl logs <pod-name> -c <container-name> to get logs from the chosen container inside the pod.

beginner

What option shows logs continuously as new lines are added?

The -f or --follow option streams the logs live, like watching a live feed. Example: kubectl logs -f <pod-name>.

intermediate

How can you get logs from previous instances of a container that crashed?

Use kubectl logs <pod-name> -c <container-name> --previous to see logs from the last terminated container.

beginner

Why is kubectl logs useful for debugging?

It helps you see what is happening inside your app running in Kubernetes. You can find errors, warnings, or understand app behavior without accessing the pod directly.

Which command streams logs live from a pod?

A kubectl get pods

B kubectl exec pod-name

C kubectl describe pod pod-name

D kubectl logs -f pod-name

The -f option in kubectl logs streams logs live as they are generated.

How do you get logs from a specific container in a pod?

A kubectl logs pod-name -c container-name

B kubectl logs pod-name --all-containers

C kubectl get logs container-name

D kubectl describe container container-name

The -c option specifies the container name inside the pod for logs.

What does the --previous flag do in kubectl logs?

A Shows logs from all containers

B Shows logs from the last terminated container

C Shows logs from the current running container

D Restarts the pod

The --previous flag shows logs from the container instance before it crashed or restarted.

Which command is NOT used to view logs?

A kubectl describe pod pod-name

B kubectl logs pod-name -f

C kubectl logs pod-name

D kubectl logs pod-name -c container-name

kubectl describe shows pod details but not logs.

Why use kubectl logs for debugging?

A To create new pods

B To delete pods

C To see app output and errors inside pods

D To update Kubernetes version

kubectl logs helps check what the app inside the pod is doing or if it has errors.

Explain how to use kubectl logs to debug a pod with multiple containers.

Think about how to target one container inside a pod.

Describe how to view logs from a crashed container to find out what went wrong.

Look for logs from the last terminated container.

Practice

1. What does the kubectl logs command do in Kubernetes?

easy

A. Deletes a pod from the cluster

B. Lists all pods running in the cluster

C. Creates a new pod with specified configuration

D. Shows the output logs of a container inside a pod

Solution

1. Step 1: Understand the purpose of kubectl logs

   This command is used to view the logs generated by containers running inside pods in Kubernetes.

2. Step 2: Differentiate from other commands

   Deleting pods uses kubectl delete, creating pods uses kubectl create, and listing pods uses kubectl get pods. None of these show logs.

3. Final Answer:

   Shows the output logs of a container inside a pod -> Option D

4. Quick Check:

   Logs = Output from container [OK]

Hint: Logs show container output, not pod creation or deletion [OK]

Common Mistakes:

• Confusing logs with pod creation or deletion
• Thinking logs list pods instead of showing output
• Assuming logs show cluster-wide events

2. Which of the following is the correct syntax to follow logs live from a pod named webapp-123?

easy

A. kubectl logs webapp-123 --follow

B. kubectl logs --tail webapp-123

C. kubectl logs webapp-123 -t

D. kubectl logs -t webapp-123

Solution

1. Step 1: Recall correct flag placement

   The --follow flag comes after the pod name in the kubectl logs command syntax.

2. Step 2: Check distractor flags

   Distractors use --tail (shows last lines, no streaming) or -t (timestamps, no follow). Only --follow streams live.

3. Final Answer:

   kubectl logs webapp-123 --follow -> Option A

4. Quick Check:

   Pod name first, then flags [OK]

Hint: Put pod name before flags like --follow [OK]

Common Mistakes:

• Placing flags before pod name
• Using --tail or -t instead of --follow
• Mixing order of arguments

3. Given the command kubectl logs mypod --tail=5, what will be the output?

medium

A. Shows all logs except the last 5 lines from the pod named mypod

B. Shows the first 5 lines of logs from the pod named mypod

C. Shows the last 5 lines of logs from the pod named mypod

D. Shows logs only if the pod has more than 5 containers

Solution

1. Step 1: Understand the --tail option

   The --tail=5 option limits the output to the last 5 lines of the logs.

2. Step 2: Confirm it applies to the specified pod

   The command targets the pod named mypod, so logs shown are from that pod only.

3. Final Answer:

   Shows the last 5 lines of logs from the pod named mypod -> Option C

4. Quick Check:

   --tail = last lines [OK]

Hint: --tail shows last lines, not first [OK]

Common Mistakes:

• Thinking --tail shows first lines
• Confusing pod logs with container logs
• Assuming it filters by container count

4. You run kubectl logs mypod -c mycontainer but get an error saying container not found. What is the likely cause?

medium

A. The pod mypod is not running

B. The container name mycontainer does not exist in pod mypod

C. You forgot to add the --follow flag

D. The pod mypod has multiple containers but you did not specify one

Solution

1. Step 1: Analyze the error message

   The error says container not found, which means the container name given is incorrect or missing in the pod.

2. Step 2: Check command correctness

   You specified -c mycontainer, so if the container name is wrong, the error appears. Pod running state or missing --follow flag does not cause this error.

3. Final Answer:

   The container name mycontainer does not exist in pod mypod -> Option B

4. Quick Check:

   Container name must match exactly [OK]

Hint: Check container name spelling matches pod's containers [OK]

Common Mistakes:

• Assuming pod state causes container not found error
• Forgetting to specify container when multiple exist
• Using wrong flag for container name

5. You want to debug a pod with two containers named frontend and backend. Which command correctly streams live logs from the backend container only?

hard

A. kubectl logs podname -c backend --follow

B. kubectl logs podname --tail -c backend

C. kubectl logs -c backend podname --tail

D. kubectl logs --tail podname -c backend

Solution

1. Step 1: Recall correct argument order

   The pod name must come immediately after kubectl logs, followed by flags like -c and --follow.

2. Step 2: Confirm container and follow flag usage

   Using -c backend specifies the backend container, and --follow streams logs live.

3. Final Answer:

   kubectl logs podname -c backend --follow -> Option A

4. Quick Check:

   Pod name first, then container and flags [OK]

Hint: Pod name first, then container (-c) and --follow [OK]

Common Mistakes:

• Placing flags before pod name
• Mixing order of container and follow flags
• Using unsupported shorthand flags