kubectl exec for container access in Kubernetes - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of kubectl exec with command

What is the output of this command if the pod myapp-pod has a container named app-container running a Linux shell?

kubectl exec myapp-pod -c app-container -- ls /tmp

A Returns an error: container app-container not found

B Shows the logs of the container app-container

C Starts an interactive shell session inside the container

D Lists files and directories inside /tmp of the container

💡 Hint

The command runs 'ls /tmp' inside the specified container.

The 'kubectl exec' command runs the given command inside the container. Here, it lists the contents of /tmp directory inside the container named 'app-container'.

💻 Command Output

intermediate

Error when container name is missing

What error will you get if you run this command on a pod with multiple containers?

kubectl exec mypod -- ls /

A Error: a container name must be specified for pod mypod, choose one of: [container1 container2]

B Lists root directory contents of the first container automatically

C Syntax error: missing container name

D Command runs successfully on all containers

💡 Hint

Pods with multiple containers require specifying which container to exec into.

When a pod has multiple containers, kubectl requires the container name to be specified with -c or --container. Otherwise, it returns an error asking to specify the container.

🔀 Workflow

advanced

Correct command to start an interactive shell inside a container

Which command correctly starts an interactive bash shell inside the container named web in pod frontend-pod?

A kubectl exec -it frontend-pod -c web -- /bin/bash

B kubectl exec frontend-pod -c web /bin/bash -i -t

C kubectl exec frontend-pod -c web --interactive --tty /bin/bash

D kubectl exec frontend-pod -c web -- bash -it

💡 Hint

Use -i and -t flags before pod name for interactive terminal.

The correct syntax is 'kubectl exec -it podname -c containername -- command'. Flags -i and -t enable interactive terminal. The command follows after '--'.

❓ Troubleshoot

advanced

Troubleshooting kubectl exec permission denied error

You run kubectl exec mypod -- cat /etc/shadow and get a permission denied error. What is the most likely reason?

A The pod is not running

B kubectl exec requires root privileges on the host machine

C The user inside the container does not have permission to read /etc/shadow

D The container image does not have /etc/shadow file

💡 Hint

File /etc/shadow is usually restricted to root user inside Linux.

The /etc/shadow file contains sensitive password info and is readable only by root or privileged users inside the container. Permission denied means the current user lacks rights.

✅ Best Practice

expert

Best practice for running commands inside containers with kubectl exec

Which practice is best when using kubectl exec to run commands inside containers in production?

A Run kubectl exec commands as root user inside containers for full access

B Always specify the container name with -c to avoid ambiguity

C Use kubectl exec without -it flags to avoid interactive sessions

D Modify container images to include debugging tools for exec commands

💡 Hint

Pods often have multiple containers; specifying container avoids mistakes.

Specifying the container name with -c ensures the command runs in the intended container, preventing errors or unintended effects. Running as root or modifying images can cause security risks.

Practice

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

easy

A. Lists all running pods in the cluster

B. Deletes a pod from the cluster

C. Creates a new pod in the cluster

D. Runs a command inside a running container in a pod

Solution

1. Step 1: Understand the purpose of kubectl exec

   The kubectl exec command is used to run commands inside a container that is already running inside a pod.

2. Step 2: Compare with other kubectl commands

   Deleting pods uses kubectl delete pod, creating pods uses kubectl create, and listing pods uses kubectl get pods. These are different commands.

3. Final Answer:

   Runs a command inside a running container in a pod -> Option D

4. Quick Check:

   kubectl exec = run command inside container [OK]

Hint: kubectl exec runs commands inside containers [OK]

Common Mistakes:

• Confusing exec with pod creation or deletion
• Thinking exec lists pods
• Using exec without specifying pod

2. Which of the following is the correct syntax to start an interactive shell inside a container named web in pod frontend-pod?

easy

A. kubectl exec -it frontend-pod -c web -- /bin/bash

B. kubectl exec frontend-pod -c web -it /bin/bash

C. kubectl exec -c web frontend-pod /bin/bash -it

D. kubectl exec frontend-pod /bin/bash -c web -it

Solution

1. Step 1: Recall correct kubectl exec syntax

   The correct syntax for interactive shell is: kubectl exec -it POD_NAME -c CONTAINER_NAME -- /bin/bash. The -it flags come before the pod name, and -- separates command from options.

2. Step 2: Analyze each option

   kubectl exec -it frontend-pod -c web -- /bin/bash matches the correct syntax exactly. The other options have misplaced flags or arguments causing syntax errors.

3. Final Answer:

   kubectl exec -it frontend-pod -c web -- /bin/bash -> Option A

4. Quick Check:

   Correct flag order and -- separator = kubectl exec -it frontend-pod -c web -- /bin/bash [OK]

Hint: Use -it before pod name and -- before command [OK]

Common Mistakes:

• Placing -it after pod name
• Omitting -- before command
• Misordering container flag -c

3. What will be the output of this command if the pod db-pod has a container named mysql running and you execute:
kubectl exec db-pod -c mysql -- ls /var/lib/mysql?

medium

A. Lists files and directories inside /var/lib/mysql in the mysql container

B. Shows an error: container mysql not found

C. Lists files in the host machine's /var/lib/mysql directory

D. Starts an interactive shell inside the mysql container

Solution

1. Step 1: Understand the command

   The command runs ls /var/lib/mysql inside the mysql container of the db-pod pod. It lists files in that directory inside the container.

2. Step 2: Eliminate wrong options

   Shows an error: container mysql not found is wrong because the container exists. Lists files in the host machine's /var/lib/mysql directory is wrong because kubectl exec runs inside container, not host. Starts an interactive shell inside the mysql container is wrong because no shell is started; only ls runs.

3. Final Answer:

   Lists files and directories inside /var/lib/mysql in the mysql container -> Option A

4. Quick Check:

   kubectl exec runs command inside container = Lists files and directories inside /var/lib/mysql in the mysql container [OK]

Hint: kubectl exec runs command inside container, not host [OK]

Common Mistakes:

• Thinking command runs on host machine
• Confusing exec with shell start
• Assuming container does not exist

4. You run kubectl exec -it mypod -- /bin/sh but get the error: error: a container name must be specified for pod mypod, choose one of: [app backend]. What is the fix?

medium

A. Restart the pod before running exec

B. Add -c app or -c backend to specify the container

C. Remove -it flags to fix the error

D. Use kubectl exec mypod /bin/sh without flags

Solution

1. Step 1: Understand the error message

   The error says multiple containers exist in pod mypod, so you must specify which container to exec into using -c.

2. Step 2: Apply the fix

   Add -c app or -c backend to the command to specify the container name explicitly.

3. Final Answer:

   Add -c app or -c backend to specify the container -> Option B

4. Quick Check:

   Multiple containers need -c flag = Add -c app or -c backend to specify the container [OK]

Hint: Specify container with -c when pod has multiple containers [OK]

Common Mistakes:

• Ignoring container name when multiple containers exist
• Removing -it flags unnecessarily
• Restarting pod without reason

5. You want to run an interactive bash shell inside the container named worker in pod job-pod. The pod has two containers: worker and logger. Which command correctly achieves this?

hard

A. kubectl exec job-pod -c worker -it /bin/bash

B. kubectl exec -it job-pod /bin/bash -c worker

C. kubectl exec -it job-pod -c worker -- /bin/bash

D. kubectl exec job-pod -it -c worker /bin/bash

Solution

1. Step 1: Recall correct syntax for interactive exec with container

   The correct syntax is kubectl exec -it POD_NAME -c CONTAINER_NAME -- /bin/bash. The -it flags come before pod name, -c specifies container, and -- separates command.

2. Step 2: Check options for correct order and flags

   kubectl exec -it job-pod -c worker -- /bin/bash matches the correct syntax exactly. The other options have misplaced flags or missing --, causing errors.

3. Final Answer:

   kubectl exec -it job-pod -c worker -- /bin/bash -> Option C

4. Quick Check:

   Correct flag order and -- separator = kubectl exec -it job-pod -c worker -- /bin/bash [OK]

Hint: Use -it before pod, -c container, and -- before command [OK]

Common Mistakes:

• Misordering flags -it and -c
• Omitting -- before command
• Not specifying container when multiple exist