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When to boot to a dump capture kernel in kdump?
Kdump uses kexec to quickly boot to a dump-capture kernel whenever a dump of the system kernel’s memory needs to be taken (for example, when the system panics). The system kernel’s memory image is preserved across the reboot and is accessible to the dump-capture kernel.
How to dump a kernel in kexec boot loader?
If you are using a relocatable kernel use CONFIG_PHYSICAL_START=0x100000 This will compile the kernel for physical address 1MB, but given the fact kernel is relocatable, it can be run from any physical address hence kexec boot loader will load it in memory region reserved for dump-capture kernel.
Is there a relocatable kernel for kdump for s390x?
For s390x, when kdump is triggered, the crashkernel region is exchanged with the region [0, crashkernel region size] and then the kdump kernel runs in [0, crashkernel region size]. Therefore no relocatable kernel is needed for s390x.
How to troubleshoot kernel crashes, hangs, or reboots?
In order to fully configure and bring the service online, the crashkernel= must be in place and chkconfig kdump on command be executed prior to a reboot. The location of the kdump vmcore can be specified in /etc/kdump.conf. You can either dump directly to a device, to a file, or to some location on the network via NFS or SSH.
How to dump vmcore in kdump by default?
(CONFIG_PROC_VMCORE is set by default when CONFIG_CRASH_DUMP is selected.) On i386, enable high memory support under “Processor type and features”: With CONFIG_SMP=y, usually nr_cpus=1 need specified on the kernel command line when loading the dump-capture kernel because one CPU is enough for kdump kernel to dump vmcore on most of systems.
Where is the core image stored in kdump?
All of the necessary information about the system kernel’s core image is encoded in the ELF format, and stored in a reserved area of memory before a crash. The physical address of the start of the ELF header is passed to the dump-capture kernel through the elfcorehdr= boot parameter.
Where to find the crash target in kdump?
The option path /var/crash represents the file system path in which the kdump saves the vmcore file. When you specify a dump target in the /etc/kdump.conf file, then the path is relative to the specified dump target.