admin-guide/kdump/kdump.rst

11 Kdump uses kexec to quickly boot to a dump-capture kernel whenever a
12 dump of the system kernel's memory needs to be taken (for example, when
14 the reboot and is accessible to the dump-capture kernel.
17 the memory image to a dump file on the local disk, or across the network
24 the dump-capture kernel. This ensures that ongoing Direct Memory Access
25 (DMA) from the system kernel does not corrupt the dump-capture kernel.
26 The kexec -p command loads the dump-capture kernel into this reserved
47 passed to the dump-capture kernel through the elfcorehdr= boot
51 With the dump-capture kernel, you can access the memory image through
52 /proc/vmcore. This exports the dump as an ELF-format file that you can
57 tool to debug the dump file. This method ensures that the dump pages are
106 Build the system and dump-capture kernels
110 1) Build a separate custom dump-capture kernel for capturing the
111    kernel core dump.
113 2) Or use the system kernel binary itself as dump-capture kernel and there is
114    no need to build a separate dump-capture kernel. This is possible
120 one does not have to build a second kernel for capturing the dump. But
121 at the same time one might want to build a custom dump capture kernel
125 dump-capture kernels for enabling kdump support.
159    This causes the kernel to be built with debug symbols. The dump
161    and analyze a dump file.
163 Dump-capture kernel config options (Arch Independent)
177 Dump-capture kernel config options (Arch Dependent, i386 and x86_64)
190    command line when loading the dump-capture kernel because one
191    CPU is enough for kdump kernel to dump vmcore on most of systems.
214    kexec boot loader will load it in memory region reserved for dump-capture
219    start of memory region reserved for dump-capture kernel.
226 Dump-capture kernel config options (Arch Dependent, ppc64)
239 Dump-capture kernel config options (Arch Dependent, arm)
247 Dump-capture kernel config options (Arch Dependent, arm64)
250 - Please note that kvm of the dump-capture kernel will not be enabled
258    Here 'size' specifies how much memory to reserve for the dump-capture kernel
261    starting at physical address 0x01000000 (16MB) for the dump-capture kernel.
344 Load the Dump-capture Kernel
347 After booting to the system kernel, dump-capture kernel needs to be
352 of dump-capture kernel. Following is the summary.
376 to load dump-capture kernel::
378    kexec -p <dump-capture-kernel-vmlinux-image> \
379    --initrd=<initrd-for-dump-capture-kernel> --args-linux \
383 to load dump-capture kernel::
385    kexec -p <dump-capture-kernel-bzImage> \
386    --initrd=<initrd-for-dump-capture-kernel> \
390 to load dump-capture kernel::
392    kexec --type zImage -p <dump-capture-kernel-bzImage> \
393    --initrd=<initrd-for-dump-capture-kernel> \
394    --dtb=<dtb-for-dump-capture-kernel> \
398 to load dump-capture kernel::
400    kexec -p <dump-capture-kernel-Image> \
401    --initrd=<initrd-for-dump-capture-kernel> \
405 loading dump-capture kernel.
427 Notes on loading the dump-capture kernel:
439   due to shared interrupts in the dump-capture kernel.
444 * Boot parameter "1" boots the dump-capture kernel into single-user
448   dump. Hence generally it is useful either to build a UP dump-capture
449   kernel or specify maxcpus=1 option while loading dump-capture kernel.
453 * You should enable multi-cpu support in dump-capture kernel if you intend
454   to use multi-thread programs with it, such as parallel dump feature of
457   SMP dump-capture kernel and specify maxcpus/nr_cpus, disable_cpu_apicid=[X]
477 After successfully loading the dump-capture kernel as previously
478 described, the system will reboot into the dump-capture kernel if a
485 will boot into the dump-capture kernel ( die_nmi() ).
489 the system will boot into the dump-capture kernel.
492 and the system will boot into the dump-capture kernel.
497 Write Out the Dump File
500 After the dump-capture kernel is booted, write out the dump file with
503    cp /proc/vmcore <dump-file>
505 or use scp to write out the dump file between hosts on a network, e.g::
507    scp /proc/vmcore remote_username@remote_ip:<dump-file>
509 You can also use makedumpfile utility to write out the dump file
512    makedumpfile -l --message-level 1 -d 31 /proc/vmcore <dump-file>
517 Before analyzing the dump image, you should reboot into a stable kernel.
519 You can do limited analysis using GDB on the dump file copied out of
523    gdb vmlinux <dump-file>
531 dump kernel.
533 You can also use the Crash utility to analyze dump files in Kdump