How To Obtain Vmcore When the Server is Unresponsive

Assuming you already have kdump configured and functioning.

If you need to generate a coredump from a server without physical access to it, you may want to allow the kernel to call the panic routine when it receives an unknown non-maskable interrupt (NMI). In order to allow it, you have to edit /etc/sysctl.conf and add the following line:

kernel.unknown_nmi_panic = 1

Apply changes with:

sysctl -p

To generate a core you may use some web-based 'KVM' services, most of them have the ability to send NMI to host. Another possible way in case of IPMI has been configured is to send unknown NMI with the impitool command:

ipmitool -I lan -H <hostname> chassis power diag

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In the case of "BUG: soft lockup - CPU#7 stuck for 67s" messages in /var/log/message, you need to switch kernel.softlockup_panic to 1 to have core file created automatically. To achieve that, edit /etc/sysctl.conf and insert the following line:

kernel.softlockup_panic = 1

Apply changes with:

sysctl -p