When a server becomes unresponsive, obtaining a VMcore (also known as a core dump or kernel dump) can be a crucial step in diagnosing the issue. A more is a snapshot of the system's memory at the time of a crash or kernel panic, which can be analyzed to identify the root cause of the problem.

Here are steps you can follow to obtain more when the server is unresponsive:

1. Check for Hardware Issues:

   • Ensure there are no physical hardware problems like loose connections, faulty RAM, or overheating.

2. Enable Kdump:

   • Kdump is a kernel crash dumping mechanism that allows the kernel to execute a second kernel on panic. Make sure it's installed and properly configured.

3. Check Disk Space:

   • Ensure you have enough free disk space to store the vmcore. Kdump typically reserves a portion of disk space for this purpose.

4. Verify Kexec is Installed and Working:

   • Kexec is a tool that allows you to load a new kernel without rebooting the system. Make sure it's installed and functioning correctly.

5. Remote Access:

   • If possible, try to access the server remotely using tools like SSH, IPMI, iLO, or DRAC.

6. Trigger a Crash:

   • If you can access the server, you can manually trigger a crash using the SysRq key combination. Pressing Alt + SysRq + c will trigger a crash.

7. Automatic Crash:

   • If the server is completely unresponsive and you cannot access it remotely, you'll have to wait for a natural crash to occur.

8. Collect more After Crash:

   • After the crash occurs, Kdump should automatically collect the vmcore and save it to the specified location.

9. Analyze the Vmcore:

   • Once you have the vmcore, you can analyze it using tools like crash, gdb, or other debugging tools. This requires knowledge of kernel internals.

10. Freeze the Vmcore for Analysis (optional):

    • If you cannot analyze the vmcore immediately, make sure to preserve it in a safe location, as it may be overwritten by subsequent crashes.

11. Document and Report:

    • Document the findings and, if necessary, report the issue to your system administrator or vendor support. Include details about the crash, the vmcore, and any relevant log files.

Remember that dealing with vmcores and kernel debugging requires advanced technical knowledge. If you're unsure about any step, it's best to consult with a qualified system administrator or support team.