Linux commands for Kubernetes users

Before working with Kubernetes, a working familiarity with the Linux command line is essential. You do not need to be a Linux expert, but certain commands come up constantly when installing tools, managing services, and troubleshooting nodes.

Here is how each category connects to your Kubernetes work:

• File system commands: you will use chmod +x when installing kubectl and other Kubernetes binaries
• Archive commands: you will use tar when extracting downloaded Kubernetes tooling
• Environment variables: you will use export to set KUBECONFIG and other Kubernetes configuration values
• Network commands: you will use ping, ss, and nslookup to diagnose connectivity issues between nodes and pods
• Process commands: you will use ps to check whether the kubelet or container runtime is running
• Service commands: you will use systemctl to manage the kubelet service and journalctl to read its logs

Essential file system commands

List files and directories in the current directory:

1ls

For detailed information including permissions, size, and modification time:

1ls -ltr

Create a new directory:

1mkdir my-directory

Switch into the directory:

1cd my-directory

Create a new empty file:

1touch myfile.txt

Edit a file with vi:

1vi myfile.txt

Press i to enter INSERT mode. Type your content. Press Escape, then type :wq! and press Enter to save and exit.

View the contents of a file:

1cat myfile.txt

Copy a file to another directory:

1cp myfile.txt ../myfile.txt

Navigate to the parent directory:

1cd ..

Clear the terminal screen:

1clear

Changing file permissions

Set a file to read-only mode:

1chmod 400 myfile.txt

Making a binary executable

When you download a Kubernetes binary like kubectl, it is not executable by default. You need to grant execute permission before you can run it.

Download the kubectl binary:

1curl -LO "https://dl.k8s.io/release/$(curl -L -s https://dl.k8s.io/release/stable.txt)/bin/linux/amd64/kubectl"

Make it executable:

1chmod +x kubectl

Run it:

1./kubectl

Extracting compressed files

Kubernetes tools are often distributed as compressed archives. Use tar to extract them:

1tar -xvf file.tar

The flags do the following: -x extracts the archive, -v lists the files as they are extracted, -f specifies the filename.

Environment variables

View all currently set environment variables:

1env

Set a new environment variable:

1export demo=training

Verify it was set:

1env | grep demo

Print the value of a variable:

1echo $demo

Expected output:

1training

Check disk space usage in a human-readable format:

1du -h

For a summary of total directory size:

1du -sh

Network connectivity commands

Test connectivity to a host:

1ping www.google.com

Send a single packet:

1ping -c 1 www.google.com

View active network connections and listening ports:

1ss -tulnp

Look up DNS records for a domain:

1nslookup www.google.com

Process status commands

View all running processes with detailed information:

1ps -ef

To terminate a process, find its PID from the ps output and run:

1kill <PID>

Tail commands

Print the last ten lines of a file:

1tail demo

Print the last five lines:

1tail -n 5 demo

Service management commands

These commands are critical for Kubernetes node troubleshooting. systemctl controls services and journalctl reads their logs.

Check the status of a service:

1systemctl status docker

Start a service:

1systemctl start docker

Check kubelet status on a Kubernetes node:

1systemctl status kubelet

View systemd logs:

1journalctl

View logs for a specific service, for example the kubelet:

1journalctl -u kubelet

Monitor CPU and memory utilisation in real time:

1top

For a more readable interface:

1htop