How to Change Default Boot Kernel

Introduction

• Welcome to the technical session on changing the default boot kernel
• Overview:
  • Importance of kernel updates
  • Step-by-step process to set default boot kernel

Context

• Using CentOS (St. Louis) Operating System (OS)
• Impact of kernel updates
• Frequent kernel updates and reboots
• Setup to load the latest kernel after reboot

Main Steps

Important Preparations

• Ensure the system has the latest kernel installed
• Need to vote system with the preferred kernel
• Change default boot kernel in Grub bootloader
• Manually edit Grub configuration file: grub.conf or grub.cfg
• Use the grubby tool to set the default kernel

Change Default Boot Kernel Using Grubby

1. Open terminal on CentOS
2. List installed kernels:

   sudo egrep ^menuentry /etc/grub2.cfg
   

   or for legacy systems:

   sudo egrep ^title /etc/grub.conf
   

3. Set default kernel:

   sudo grubby --set-default=/boot/vmlinuz-<kernel-version>
   

4. Verify changes:

   grubby --default-kernel
   

Validate System Boot

• Reboot the system
• Ensure the system boots with the new default kernel
• Use uname -r to check running kernel version

Conclusion

• Successfully changed the default boot kernel
• Verification and validation steps

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