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.
155    This causes the kernel to be built with debug symbols. The dump
157    and analyze a dump file.
159 Dump-capture kernel config options (Arch Independent)
177 Dump-capture kernel config options (Arch Dependent, i386 and x86_64)
186    command line when loading the dump-capture kernel because one
187    CPU is enough for kdump kernel to dump vmcore on most of systems.
208    kexec boot loader will load it in memory region reserved for dump-capture
213    start of memory region reserved for dump-capture kernel.
220 Dump-capture kernel config options (Arch Dependent, ppc64)
233 Dump-capture kernel config options (Arch Dependent, arm)
241 Dump-capture kernel config options (Arch Dependent, arm64)
244 - Please note that kvm of the dump-capture kernel will not be enabled
252    Here 'size' specifies how much memory to reserve for the dump-capture kernel
255    starting at physical address 0x01000000 (16MB) for the dump-capture kernel.
338 Load the Dump-capture Kernel
341 After booting to the system kernel, dump-capture kernel needs to be
346 of dump-capture kernel. Following is the summary.
370 to load dump-capture kernel::
372    kexec -p <dump-capture-kernel-vmlinux-image> \
373    --initrd=<initrd-for-dump-capture-kernel> --args-linux \
377 to load dump-capture kernel::
379    kexec -p <dump-capture-kernel-bzImage> \
380    --initrd=<initrd-for-dump-capture-kernel> \
384 to load dump-capture kernel::
386    kexec --type zImage -p <dump-capture-kernel-bzImage> \
387    --initrd=<initrd-for-dump-capture-kernel> \
388    --dtb=<dtb-for-dump-capture-kernel> \
392 to load dump-capture kernel::
394    kexec -p <dump-capture-kernel-Image> \
395    --initrd=<initrd-for-dump-capture-kernel> \
399 loading dump-capture kernel.
421 Notes on loading the dump-capture kernel:
433   due to shared interrupts in the dump-capture kernel.
438 * Boot parameter "1" boots the dump-capture kernel into single-user
442   dump. Hence generally it is useful either to build a UP dump-capture
443   kernel or specify maxcpus=1 option while loading dump-capture kernel.
447 * You should enable multi-cpu support in dump-capture kernel if you intend
448   to use multi-thread programs with it, such as parallel dump feature of
451   SMP dump-capture kernel and specify maxcpus/nr_cpus options while loading it.
470 After successfully loading the dump-capture kernel as previously
471 described, the system will reboot into the dump-capture kernel if a
478 will boot into the dump-capture kernel ( die_nmi() ).
482 the system will boot into the dump-capture kernel.
485 and the system will boot into the dump-capture kernel.
490 Write Out the Dump File
493 After the dump-capture kernel is booted, write out the dump file with
496    cp /proc/vmcore <dump-file>
498 or use scp to write out the dump file between hosts on a network, e.g::
500    scp /proc/vmcore remote_username@remote_ip:<dump-file>
502 You can also use makedumpfile utility to write out the dump file
505    makedumpfile -l --message-level 1 -d 31 /proc/vmcore <dump-file>
510 Before analyzing the dump image, you should reboot into a stable kernel.
512 You can do limited analysis using GDB on the dump file copied out of
516    gdb vmlinux <dump-file>
524 dump kernel.
526 You can also use the Crash utility to analyze dump files in Kdump