kubectl exec for container access in Kubernetes - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the command kubectl exec do?

It lets you run commands inside a running container in a Kubernetes pod, like opening a terminal session or running a script.

beginner

How do you open an interactive shell inside a container using kubectl exec?

Use kubectl exec -it <pod-name> -- /bin/sh or /bin/bash to start an interactive shell session.

beginner

What does the -i and -t flags mean in kubectl exec -it?

-i keeps the input open (interactive), and -t allocates a terminal, so you can type commands like in a normal shell.

intermediate

How do you specify which container to exec into if a pod has multiple containers?

Use the -c <container-name> option to choose the container inside the pod.

beginner

What happens if you run kubectl exec <pod-name> -- ls /?

It runs the ls / command inside the container, listing the root directory contents without opening an interactive shell.

Which command opens an interactive bash shell inside a pod named 'webapp'?

A kubectl shell webapp

B kubectl exec -it webapp -- /bin/bash

C kubectl get pods webapp --shell

D kubectl run webapp -- /bin/bash

The correct syntax to open an interactive shell is 'kubectl exec -it pod-name -- /bin/bash'.

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

A Specifies the pod namespace

B Ends the command

C Separates kubectl options from the command to run inside the container

D Indicates the container name

The double dash -- tells kubectl that what follows is the command to run inside the container.

If a pod has two containers, how do you run a command in the second container?

A kubectl exec pod -c container2 -- command

B kubectl exec pod --container container2 command

C kubectl exec pod container2 -- command

D kubectl exec pod --container=container2 command

Use the -c flag followed by the container name to specify which container to exec into.

What is the purpose of the -t flag in kubectl exec -it?

A Allocates a pseudo-TTY (terminal)

B Runs the command in the background

C Specifies the target pod

D Terminates the session after command

The -t flag allocates a terminal so you can interact with the shell.

Which command lists files in the root directory of a pod named 'db' without opening a shell?

A kubectl exec db ls /

B kubectl exec -it db -- ls /

C kubectl exec db -c ls /

D kubectl exec db -- ls /

Running 'kubectl exec db -- ls /' executes the command directly inside the container.

Explain how to use kubectl exec to open an interactive shell inside a container.

Think about how to connect to a container like opening a terminal.

Describe the difference between running a command with kubectl exec interactively and non-interactively.

Consider when you want to type commands versus just get results.

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