Executing commands in Pods in Kubernetes - Cheat Sheet & Quick Revision

Recall & Review

beginner

What command is used to execute a command inside a running Kubernetes Pod?

The command kubectl exec is used to run commands inside a running Pod.

beginner

How do you start an interactive shell session inside a Pod named my-pod?

Use kubectl exec -it my-pod -- /bin/sh or kubectl exec -it my-pod -- /bin/bash to start an interactive shell.

beginner

What does the -it flag mean in kubectl exec?

-i means interactive (keeps stdin open), and -t allocates a terminal. Together they allow interactive shell sessions.

intermediate

Can you execute commands in a specific container inside a Pod with multiple containers? How?

Yes, use kubectl exec -it pod-name -c container-name -- command to target a specific container.

beginner

What happens if you run kubectl exec on a Pod that is not running?

The command will fail because the Pod must be in a running state to execute commands inside it.

Which command runs an interactive bash shell inside a Pod named 'web-server'?

A kubectl exec -it web-server -- /bin/bash

B kubectl run web-server -- /bin/bash

C kubectl start web-server -bash

D kubectl shell web-server

Option A uses the correct syntax to execute an interactive bash shell inside the Pod.

What does the -- signify in the command kubectl exec pod-name -- ls?

A Ends the command execution

B Separates kubectl flags from the command to run inside the Pod

C Specifies the Pod namespace

D Indicates the Pod name

The -- separates kubectl options from the command to run inside the Pod.

How do you specify a container inside a Pod when executing a command?

A --container container-name

B -p container-name

C -c container-name

D -n container-name

The -c flag specifies the container name inside the Pod.

If you want to run a non-interactive command like ls / inside a Pod, which flag is NOT necessary?

A -c

B -i

C --

D -t

The -t flag allocates a terminal and is not needed for non-interactive commands.

What will happen if you try to exec into a Pod that is in 'Pending' state?

A The command will fail because the Pod is not running

B You will get a shell prompt

C The Pod will start automatically

D kubectl will restart the Pod

You cannot exec into a Pod unless it is running.

Explain how to run an interactive shell inside a Kubernetes Pod and why the flags used are important.

Think about how you connect to a remote computer's terminal.

Describe how to execute a command inside a specific container when a Pod has multiple containers.

Imagine a Pod like a small apartment with multiple rooms (containers).

Practice

1. What is the primary purpose of the kubectl exec command in Kubernetes?

easy

A. To list all Pods in a namespace

B. To create a new Pod

C. To run commands inside a running Pod

D. To delete a Pod

Solution

1. Step 1: Understand the function of kubectl exec

   The kubectl exec command is used to execute commands inside a running Pod's container.

2. Step 2: Differentiate from other commands

   Creating, deleting, or listing Pods are done with other commands like kubectl create, kubectl delete, and kubectl get.

3. Final Answer:

   To run commands inside a running Pod -> Option C

4. Quick Check:

   kubectl exec runs commands inside Pods [OK]

Hint: Remember: exec means execute inside Pod [OK]

Common Mistakes:

• Confusing exec with create or delete commands
• Thinking exec lists Pods
• Using exec to start new Pods

2. Which of the following is the correct syntax to run the command ls /app inside a Pod named web-pod?

easy

A. kubectl exec web-pod ls /app

B. kubectl exec web-pod -- ls /app

C. kubectl exec -- web-pod ls /app

D. kubectl exec -c web-pod ls /app

Solution

1. Step 1: Identify correct command separator

   The -- separates the Pod name from the command to run inside the Pod.

2. Step 2: Apply syntax rules

   The correct syntax is kubectl exec [pod-name] -- [command], so kubectl exec web-pod -- ls /app is correct.

3. Final Answer:

   kubectl exec web-pod -- ls /app -> Option B

4. Quick Check:

   Use -- before command [OK]

Hint: Use double dash (--) before command [OK]

Common Mistakes:

• Omitting the -- separator
• Placing -- before Pod name
• Using -c without container name

3. Given a Pod named db-pod with two containers: mysql and backup, what is the output of this command?

kubectl exec db-pod -c backup -- echo Hello

medium

A. Pod not found

B. Error: container name required

C. No such container: backup

D. Hello

Solution

1. Step 1: Understand the command components

   The command runs echo Hello inside the backup container of the db-pod Pod.

2. Step 2: Predict the command output

   Since the container exists and the command is valid, it outputs Hello.

3. Final Answer:

   Hello -> Option D

4. Quick Check:

   Correct container specified with -c outputs command result [OK]

Hint: Use -c to specify container, output is command result [OK]

Common Mistakes:

• Not specifying container when multiple exist
• Using wrong container name
• Expecting Pod name as container

4. You run this command but get an error:

kubectl exec mypod ls /data

What is the most likely cause?

medium

A. Missing -- before the command

B. Pod mypod does not exist

C. The ls command is invalid

D. You need to specify the container with -c

Solution

1. Step 1: Check command syntax

   The command is missing the -- separator between Pod name and command.

2. Step 2: Understand effect of missing --

   Without --, kubectl treats ls as a Pod or option, causing an error.

3. Final Answer:

   Missing -- before the command -> Option A

4. Quick Check:

   Always use -- before command [OK]

Hint: Always put -- before command to avoid errors [OK]

Common Mistakes:

• Forgetting the -- separator
• Assuming container must be specified when only one exists
• Thinking command is invalid

5. You want to run cat /etc/config inside the app-container of Pod multi-pod which has three containers. Which command is correct?

hard

A. kubectl exec multi-pod -c app-container -- cat /etc/config

B. kubectl exec multi-pod cat /etc/config -c app-container

C. kubectl exec -c app-container multi-pod cat /etc/config

D. kubectl exec multi-pod -- -c app-container cat /etc/config

Solution

1. Step 1: Identify correct order of options

   The -c option specifying the container must come after the Pod name and before the -- separator.

2. Step 2: Confirm command separator usage

   The -- must separate the Pod/container specification from the command to run.

3. Step 3: Validate each option

   kubectl exec multi-pod -c app-container -- cat /etc/config correctly places -c app-container before -- and then the command cat /etc/config.

4. Final Answer:

   kubectl exec multi-pod -c app-container -- cat /etc/config -> Option A

5. Quick Check:

   -c before --, then command [OK]

Hint: Put -c before --, then command [OK]

Common Mistakes:

• Placing -c after the command
• Putting -- before -c
• Omitting -- separator