Month: January 2025

LEAPP upgrade – multiple kernel issue

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Newest installed kernel not in use

If the newest installed kernel is not in use even after rebooting, it typically means your system is booting into an older kernel version. This happens due to the default GRUB settings or other configuration issues.

Here’s how you can resolve the issue step-by-step:

1. Verify the Currently Running Kernel

  • Check the kernel currently in use:

uname -r

  • Example output:

CopyEdit

3.10.0-1127.el7.x86_64

  • Compare this with the newest installed kernel version (see step 2).

2. List All Installed Kernels

  • List all installed kernel packages:

rpm -qa | grep kernel | grep -v firmware

  • Example output:

kernel-3.10.0-1127.el7.x86_64

kernel-3.10.0-1160.el7.x86_64

  • Identify the newest kernel (e.g., 3.10.0-1160.el7.x86_64).

3. Check GRUB Default Boot Entry

  • Display the current GRUB default boot entry:

grub2-editenv list

  • You should see something like this:

saved_entry=0

  • If the saved_entry is pointing to an older kernel, the system is booting into it by default.

4. Update GRUB to Use the Newest Kernel

Option A: Use the First Kernel (Default GRUB Behavior)

  • Edit the GRUB configuration:

sudo vi /etc/default/grub

  • Set the GRUB_DEFAULT value to 0 (the first kernel in the GRUB list):

GRUB_DEFAULT=0

  • Save and exit the file.
  • Regenerate the GRUB configuration:

sudo grub2-mkconfig -o /boot/grub2/grub.cfg

Option B: Manually Specify the Newest Kernel

  • Run this command to view all available kernel entries:

awk -F\’ ‘$1==”menuentry ” {print i++ ” : ” $2}’ /boot/grub2/grub.cfg

  • Example output:

0 : CentOS Linux (3.10.0-1160.el7.x86_64)

1 : CentOS Linux (3.10.0-1127.el7.x86_64)

2 : CentOS Linux (0-rescue-…)

  • Set GRUB_DEFAULT to the corresponding entry for the newest kernel (e.g., 0):

sudo grub2-set-default 0

  • Verify the setting:

grub2-editenv list

5. Reboot the System

  • Reboot your system to load the correct kernel:

sudo reboot

  • After reboot, confirm that the new kernel is in use:

uname -r

6. Remove Old Kernels (Optional)

  • To prevent confusion in the future, you can remove unused older kernels:

sudo package-cleanup –oldkernels –count=1

  • This retains only the most recent kernel.

7. Troubleshooting

  • Manually Select the Kernel: If the system still boots into the wrong kernel, you can manually select the desired kernel during the GRUB menu at boot time. To enable the GRUB menu:
    1. Edit /etc/default/grub:

sudo vi /etc/default/grub

  • Set GRUB_TIMEOUT to a non-zero value (e.g., 5):

GRUB_TIMEOUT=5

  • Save and regenerate the GRUB configuration:

sudo grub2-mkconfig -o /boot/grub2/grub.cfg

  • Kernel Missing After Update: Ensure the new kernel is properly installed. Reinstall it if necessary:

sudo yum install kernel

Istio

techhadoop

What is istio ?

Istio is an open-source service mesh platform that helps manage, secure, and monitor communication between microservices in distributed systems, such as Kubernetes-based applications. It abstracts the complexity of service-to-service communication and provides powerful capabilities without requiring changes to application code.

Key Features of Istio

  1. Traffic Management
    • Provides fine-grained control over service traffic.
    • Features include:
      • Load balancing.
      • Traffic routing (e.g., blue-green deployments, canary releases).
      • Traffic splitting by percentage.
      • Retry and failover mechanisms.
  2. Security
    • Enables mutual TLS (mTLS) for secure communication between services.
    • Provides service-level identity, authentication, and authorization.
    • Supports encryption of data in transit.
  3. Observability
    • Provides monitoring and tracing capabilities for service communication.
    • Integrates with tools like Prometheus, Grafana, and Jaeger for metrics and distributed tracing.
    • Offers detailed logs and dashboards for understanding service health and performance.
  4. Service Resilience
    • Provides fault injection to test resilience.
    • Circuit breakers and timeouts for handling failing services gracefully.
    • Automatic retries for transient failures.
  5. Policy Enforcement
    • Allows applying policies at runtime (e.g., rate limiting, quotas).
    • Helps enforce compliance with organizational or regulatory requirements.

How Istio Works

Istio operates by introducing sidecars and control planes:

  1. Sidecar Proxy
    • Istio uses Envoy as a sidecar proxy.
    • A proxy container is injected alongside each service container in a pod.
    • The proxy intercepts and manages all inbound and outbound traffic for the service.
  2. Control Plane
    • The control plane (typically managed by the Istiod component) oversees configuration, policy enforcement, and secure communication setup.
    • It communicates with all sidecar proxies to enforce desired traffic behavior.

Use Cases for Istio

  1. Service Mesh for Microservices
    • Manage the complexity of service communication in large microservices environments.
  2. Zero-Trust Security
    • Implement mTLS and fine-grained access control between services.
  3. Traffic Splitting
    • Perform canary deployments or A/B testing by routing a percentage of traffic to different service versions.
  4. Observability
    • Gain deep insights into service interactions with metrics, logs, and traces.
  5. Policy Enforcement
    • Apply runtime policies to ensure reliability and security.

Istio Architecture

Istio’s architecture consists of the following components:

  1. Envoy Proxy:
    • Data plane component responsible for service-to-service communication.
    • Handles traffic routing, load balancing, and security (e.g., mTLS).
  2. Istiod:
    • Central control plane that configures proxies and enforces policies.
    • Provides service discovery, certificate management, and telemetry data.
  3. Telemetry Tools:
    • Istio collects metrics, logs, and traces to integrate with monitoring tools like Prometheus, Grafana, and Jaeger.

Istio vs Traditional Load Balancers

  • Istio provides layer 7 (application layer) traffic management, unlike traditional load balancers which mostly focus on layer 4 (transport layer).
  • It can dynamically route traffic based on HTTP headers, cookies, or other data, which makes it ideal for modern microservice architectures.

When to Use Istio

Use Istio if:

  • Your application involves multiple microservices that need traffic management and security.
  • You need advanced observability for troubleshooting and monitoring.
  • You’re running Kubernetes or containerized workloads at scale.
  • You want to implement fine-grained traffic controls, such as canary or blue-green deployments.

Ansible – host list

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The error “host list declined parsing host file as it did not pass its verify_file() method” occurs when Ansible cannot properly parse your inventory file. This is typically due to an invalid format or incorrect file structure. Here’s how to troubleshoot and fix it:

Step 1: Verify Inventory File Format

Correct INI Format Example

Ensure your inventory file uses the proper INI-style syntax:

[webservers]

web1 ansible_host=192.168.1.10 ansible_user=root

web2 ansible_host=192.168.1.11 ansible_user=root

[dbservers]

db1 ansible_host=192.168.1.20 ansible_user=root

Correct YAML Format Example

If using a YAML-based inventory file, ensure it follows the correct structure:

all:

  hosts:

    web1:

      ansible_host: 192.168.1.10

      ansible_user: root

    web2:

      ansible_host: 192.168.1.11

      ansible_user: root

  children:

    dbservers:

      hosts:

        db1:

          ansible_host: 192.168.1.20

          ansible_user: root

Step 2: Check File Extension

  • For INI-style inventory, use .ini or no extension (e.g., inventory).
  • For YAML-style inventory, use .yaml or .yml.

Step 3: Test the Inventory File

Use the ansible-inventory command to validate the inventory file:

ansible-inventory -i inventory –list

  • Replace inventory with the path to your inventory file.
  • If there’s an error, it will provide details about what’s wrong.

 Step 4: Use Explicit Inventory Path

When running an Ansible command or playbook, explicitly specify the inventory file:

ansible all -i /path/to/inventory -m ping

 Step 5: Check Syntax Errors

  1. Ensure there are no trailing spaces or unexpected characters in your inventory file.
  2. Use a linter for YAML files if you suspect a YAML formatting issue:

yamllint /path/to/inventory.yaml

 Step 6: Set Permissions

Ensure the inventory file has the correct permissions so that Ansible can read it:

chmod 644 /path/to/inventory

Leapp

techhadoop

Leapp is a tool provided by Red Hat for performing in-place upgrades of Red Hat Enterprise Linux (RHEL) systems. It helps users upgrade from one major version of RHEL to another without needing to reinstall the entire system1. This means you can move from, say, RHEL 7 to RHEL 8 or RHEL 8 to RHEL 9, while keeping your system configurations, custom repositories, and third-party applications intact.

Ansible playbook to run a shell script on your remote hosts:

techhadoop , , , , 

#!/bin/bash
# example_script.sh

echo "Hello, this is a sample script."
echo "Current date and time: $(date)"

ansible 

---
- name: Run Shell Script on Remote Hosts
  hosts: all
  become: yes
  tasks:
    - name: Copy Shell Script to Remote Hosts
      copy:
        src: /path/to/example_script.sh
        dest: /tmp/example_script.sh
        mode: '0755'

    - name: Run Shell Script
      command: /tmp/example_script.sh

    - name: Remove Shell Script from Remote Hosts
      file:
        path: /tmp/example_script.sh
        state: absent

Explanation:
Copy Shell Script: The copy module is used to transfer the shell script from the local machine to the remote hosts. The mode parameter ensures that the script is executable.

Run Shell Script: The command module is used to execute the shell script on the remote hosts.

Remove Shell Script: The file module is used to delete the shell script from the remote hosts after execution to clean up.

Running the Playbook:
To run the playbook, use the following command:

initramfs

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What is initramfs ?

initramfs stands for initial RAM filesystem. It plays a crucial role in the Linux boot process by providing a temporary root filesystem that is loaded into memory. This temporary root filesystem contains the necessary drivers, tools, and scripts needed to mount the real root filesystem and continue the boot process.

In simpler terms, it acts as a bridge between the bootloader and the main operating system, ensuring that the system has everything it needs to boot successfully.

Key Concepts of initramfs:

FeatureDescription
Temporary FilesystemIt’s loaded into memory as a temporary root filesystem.
Kernel ModulesContains drivers (kernel modules) required to access disks, filesystems, and other hardware.
ScriptsContains initialization scripts to prepare the system for booting the real root filesystem.
Critical FilesIncludes essential tools like mount, udev, bash, and libraries.

Key Functions of initramfs:

  1. Kernel Initialization: During the boot process, the Linux kernel loads the initramfs into memory.
  2. Loading Drivers: initramfs includes essential drivers needed to access hardware components, such as storage devices and filesystems.
  3. Mounting Root Filesystem: The primary function of initramfs is to mount the real root filesystem from a storage device (e.g., hard drive, SSD).
  4. Transitioning to Real Root: Once the real root filesystem is mounted, the initramfs transitions control to the system’s main init process, allowing the boot process to continue.

How initramfs Works:

  1. Bootloader Stage: The bootloader (e.g., GRUB) loads the Linux kernel and initramfs into memory.
  2. Kernel Stage: The kernel initializes and mounts the initramfs as the root filesystem.
  3. Init Stage: The init script or program within initramfs runs, performing tasks such as loading additional drivers, mounting filesystems, and locating the real root filesystem.
  4. Switch Root: The initramfs mounts the real root filesystem and switches control to it, allowing the system to boot normally.

Customizing initramfs:

You can customize the initramfs by including specific drivers, tools, and scripts. This is useful for scenarios where the default initramfs does not include the necessary components for your system.

Tools for Managing initramfs:

  • mkinitramfs: A tool to create initramfs images.
  • update-initramfs: A tool to update existing initramfs images.

Difference Between initramfs and initrd

Featureinitramfsinitrd
Formatcpio archive (compressed)Disk image (block device)
MountingExtracted directly into RAM as a rootfsMounted as a loop device
FlexibilityMore flexible and fasterLess flexible, older technology

Location of initramfs

On most Linux distributions, the initramfs file is located in the /boot directory:

ls /boot/initramfs-*.img

How to Rebuild initramfs

If you’ve made changes to the kernel, /etc/fstab, or storage configuration (e.g., LUKS, LVM), you may need to rebuild the initramfs.

Rebuild initramfs on RHEL/CentOS:

sudo dracut -f

Rebuild initramfs on Ubuntu/Debian:

sudo update-initramfs -u

Common Issues Related to initramfs

IssueCauseSolution
Dropped into initramfs shellKernel can’t find the root filesystemCheck /etc/fstab, rebuild initramfs, or fix missing drivers.
Boot failure after kernel updateMissing or corrupt initramfsRebuild initramfs.
Filesystem not mountingIncorrect or missing drivers in initramfsEnsure necessary drivers are included and rebuild.

By understanding how initramfs works, you can better appreciate its role in the Linux boot process and customize it to suit your needs.

Upgrade RHEL 7 to RHEL 8 – ansible playbook

techhadoop , , , , 

---
- name: Upgrade RHEL 7 to RHEL 8
  hosts: all
  become: true
  vars:
    leapp_repo: "rhel-7-server-extras-rpms"

  tasks:
    - name: Ensure system is up to date
      yum:
        name: '*'
        state: latest

    - name: Install the Leapp utility
      yum:
        name: leapp
        state: present
        enablerepo: "{{ leapp_repo }}"

    - name: Run the pre-upgrade check with Leapp
      shell: leapp preupgrade
      register: leapp_preupgrade
      ignore_errors: true

    - name: Check for pre-upgrade issues
      debug:
        msg: "Leapp pre-upgrade check output: {{ leapp_preupgrade.stdout }}"

    - name: Fix any issues identified by Leapp (manual step)
      pause:
        prompt: "Please review the pre-upgrade report at /var/log/leapp/leapp-report.txt and fix any blocking issues. Press Enter to continue."

    - name: Proceed with the upgrade
      shell: leapp upgrade
      ignore_errors: true

    - name: Reboot the server to complete the upgrade
      reboot:
        reboot_timeout: 1200

    - name: Verify the OS version after reboot
      shell: cat /etc/redhat-release
      register: os_version

    - name: Display the new OS version
      debug:
        msg: "The server has been successfully upgraded to: {{ os_version.stdout }}"

How to use LUKS data disk encryption in MapR

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How to use LUKS data disk encryption in MapR

MapR (now part of HPE Ezmeral) supports encryption at various levels, but using LUKS (Linux Unified Key Setup) encryption for data disks is a system-level operation that must be done outside of MapR’s native encryption features. Here’s a step-by-step guide to set up LUKS disk encryption on a MapR node and ensure MapR can access the encrypted disk after unlocking it.

Steps to Set Up LUKS Disk Encryption for MapR Data Disks

1. Identify the Disk to Encrypt

Find the disk you want to encrypt using the lsblk or fdisk command:

bash

lsblk

fdisk -l

For example, if the disk to be encrypted is /dev/sdb, use that in the following steps.

2. Install the Necessary Packages

Ensure you have the required tools to set up LUKS encryption:

sudo apt-get install cryptsetup  # For Ubuntu/Debian

sudo yum install cryptsetup      # For CentOS/RHEL

3. Set Up LUKS Encryption on the Disk

Run the following command to initialize the disk with LUKS encryption:

sudo cryptsetup luksFormat /dev/sdb

You’ll be prompted to confirm the operation and set a passphrase.

⚠️ Warning: This will erase all existing data on the disk.

4. Open and Map the Encrypted Disk

Unlock the encrypted disk and map it to a device:

sudo cryptsetup open /dev/sdb mapr_data_disk

You can verify that the encrypted device is available:

lsblk

5. Format the Encrypted Disk

Format the newly mapped device with a filesystem that MapR supports (typically ext4 or xfs):

sudo mkfs.ext4 /dev/mapper/mapr_data_disk

6. Mount the Encrypted Disk

Create a mount point and mount the encrypted disk:

sudo mkdir -p /opt/mapr/data

sudo mount /dev/mapper/mapr_data_disk /opt/mapr/data

7. Make the Mount Persistent

Edit the /etc/crypttab file to automatically unlock the disk at boot:

echo “mapr_data_disk /dev/sdb none luks” | sudo tee -a /etc/crypttab

Then, add an entry to /etc/fstab to mount the disk automatically after it is unlocked:

echo “/dev/mapper/mapr_data_disk /opt/mapr/data ext4 defaults 0 0” | sudo tee -a /etc/fstab

8. Ensure MapR Can Access the Disk

Make sure the MapR user has the necessary permissions to access the encrypted disk:

sudo chown -R mapr:mapr /opt/mapr/data

9. Test the Setup

Reboot the system to ensure the encrypted disk is unlocked and mounted correctly:

sudo reboot

After the system reboots, verify that the disk is unlocked and mounted:

lsblk

df -h

10. Verify MapR Storage Pools

After the encrypted disk is mounted, add it to the MapR storage pool:

maprcli disk add -server <server_name> -disks /dev/mapper/mapr_data_disk

Additional Considerations

  • Passphrase Management: Consider integrating with a key management system (KMS) to avoid manual passphrase entry.
  • Performance Impact: Encryption may introduce some performance overhead, so test accordingly.
  • Backup Configuration Files: Ensure you back up /etc/crypttab and /etc/fstab for disaster recovery.