unable to see grub menu option after boot.

Hey Rakesh,

From what I've been able to grasp, you've modified the upstream kernel within your Linode, and are still using GRUB 2, but are unable to invoke the GRUB menu at system boot? I attempted to replicate this behavior by spinning up a new CentOS 7 Linode, but was unable to get the GRUB menu to appear. I'll be totally honest, It's not often that I work with GRUB on a CentOS machine, so it would be useful to have you walk us through the steps you've taken thus far. I'll assume you've run sudo yum update kernel after modifying your kernel. If not, definitely give that a try.

• Updating the Upstream Kernel on a Linode | Linode Docs

If anyone else in the community has additional tenure with GRUB and CentOS, please feel free to chime in.

Hope this helps!

-- Eric

After spending some extra time investigating, I believe I've discovered the solution you were seeking to make the GRUB selection screen persist upon boot. Here's what I did:

1. I began by setting up a new CentOS 7 Linode, which defaulted to GRUB2 with version 3.10.0-1160.90.1.el7.x86_64.

   uname -r
   3.10.0-1160.90.1.el7.x86_64
   

2. Next, I accessed the Linode via SSH.

3. In the /etc/default/grub file, I adjusted the timeout setting from 5 to 25 seconds:

   GRUB_TIMEOUT=25
   

4. Following this, I updated the kernel using the command:

   sudo yum update kernel
   

   This action introduced the kernel.x86_64 0:3.10.0-1160.102.1.el7 kernel to the system.

5. Then, I replaced the grub.cfg file by executing:

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

6. Finally, I initiated a reboot of the Linode by using the Reboot button in the Cloud Manager.

Upon reboot, I found myself directly at the GRUB selection screen, without the need to press 'shift'. From there, I could easily navigate between the 3.10.0-1160.90.1.el7.x86_64 and 3.10.0-1160.102.1.el7.x86.64 kernels using the arrow keys. Selecting the desired kernel allowed the Linode to boot successfully.

The only differences in the regenerated grub.cfg file are the ones outlined above so it seems that including the secondary kernel in the grub.cfg file triggers the system to consistently prompt the user for a kernel selection.

A couple of additional important points to note:

• I closed and reopened Lish immediately after clicking Reboot to effectively 'reset' the Lish session. I've noticed Lish can be a bit temperamental, and this step helped mitigate any erratic behavior.

• I maintained the Linode in para-virtualization mode and kept all helper switches at their default settings throughout the process.

Cheers,

-- Eric