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2 Documentation for Kdump - The kexec-based Crash Dumping Solution
11 Kdump uses kexec to quickly boot to a dump-capture kernel whenever a
13 the system panics). The system kernel's memory image is preserved across
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
44 All of the necessary information about the system kernel's core image is
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
55 options, e.g with '-d 31' it will only write out kernel data. Further,
63 Install kexec-tools
64 -------------------
68 2) Download the kexec-tools user-space package from the following URL:
70 http://kernel.org/pub/linux/utils/kernel/kexec/kexec-tools.tar.gz
74 The latest kexec-tools git tree is available at:
76 - git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
77 - http://www.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
80 http://www.kernel.org/git/?p=utils/kernel/kexec/kexec-tools.git
82 More information about kexec-tools can be found at
87 tar xvpzf kexec-tools.tar.gz
89 4) Change to the kexec-tools directory, as follows::
91 cd kexec-tools-VERSION
106 Build the system and dump-capture kernels
107 -----------------------------------------
110 1) Build a separate custom dump-capture kernel for capturing the
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
125 dump-capture kernels for enabling kdump support.
128 ----------------------------
131 "Processor type and features."::
143 2) Enable "sysfs file system support" in "Filesystem" -> "Pseudo
163 Dump-capture kernel config options (Arch Independent)
164 -----------------------------------------------------
166 1) Enable "kernel crash dumps" support under "Processor type and
171 2) Enable "/proc/vmcore support" under "Filesystems" -> "Pseudo filesystems"::
177 Dump-capture kernel config options (Arch Dependent, i386 and x86_64)
178 --------------------------------------------------------------------
180 1) On i386, enable high memory support under "Processor type and
190 command line when loading the dump-capture kernel because one
196 admin-guide/kernel-parameters.txt for more details.
201 enable "Build a relocatable kernel" support under "Processor type and
207 loaded" (under "Processor type and features"). This only appears when
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)
227 ----------------------------------------------------------
239 Dump-capture kernel config options (Arch Dependent, ia64)
240 ----------------------------------------------------------
242 - No specific options are required to create a dump-capture kernel
245 as a dump-capture kernel if desired.
257 Dump-capture kernel config options (Arch Dependent, arm)
258 ----------------------------------------------------------
260 - To use a relocatable kernel,
265 Dump-capture kernel config options (Arch Dependent, arm64)
266 ----------------------------------------------------------
268 - Please note that kvm of the dump-capture kernel will not be enabled
269 on non-VHE systems even if it is configured. This is because the CPU
276 Here 'size' specifies how much memory to reserve for the dump-capture kernel
279 starting at physical address 0x01000000 (16MB) for the dump-capture kernel.
300 on the value of System RAM -- that's mostly for distributors that pre-setup
307 range=start-[end]
311 crashkernel=512M-2G:64M,2G-:128M
339 -----------------------
353 dump-capture kernel config option notes above.
361 kernel will automatically locate the crash kernel image within the
367 Load the Dump-capture Kernel
370 After booting to the system kernel, dump-capture kernel needs to be
373 Based on the architecture and type of image (relocatable or not), one
375 of dump-capture kernel. Following is the summary.
379 - Use bzImage/vmlinuz if kernel is relocatable.
380 - Use vmlinux if kernel is not relocatable.
384 - Use vmlinux
388 - Use vmlinux or vmlinuz.gz
392 - Use image or bzImage
396 - Use zImage
400 - Use vmlinux or Image
402 If you are using an uncompressed vmlinux image then use following command
403 to load dump-capture kernel::
405 kexec -p <dump-capture-kernel-vmlinux-image> \
406 --initrd=<initrd-for-dump-capture-kernel> --args-linux \
407 --append="root=<root-dev> <arch-specific-options>"
410 to load dump-capture kernel::
412 kexec -p <dump-capture-kernel-bzImage> \
413 --initrd=<initrd-for-dump-capture-kernel> \
414 --append="root=<root-dev> <arch-specific-options>"
417 to load dump-capture kernel::
419 kexec --type zImage -p <dump-capture-kernel-bzImage> \
420 --initrd=<initrd-for-dump-capture-kernel> \
421 --dtb=<dtb-for-dump-capture-kernel> \
422 --append="root=<root-dev> <arch-specific-options>"
424 If you are using an uncompressed Image, then use following command
425 to load dump-capture kernel::
427 kexec -p <dump-capture-kernel-Image> \
428 --initrd=<initrd-for-dump-capture-kernel> \
429 --append="root=<root-dev> <arch-specific-options>"
431 Please note, that --args-linux does not need to be specified for ia64.
432 It is planned to make this a no-op on that architecture, but for now
436 loading dump-capture kernel.
458 Notes on loading the dump-capture kernel:
463 So, on non-PAE systems, ELF32 is always used.
465 The --elf32-core-headers option can be used to force the generation of ELF32
467 with ELF64 headers on 32-bit systems.
470 due to shared interrupts in the dump-capture kernel.
472 * You must specify <root-dev> in the format corresponding to the root
475 * Boot parameter "1" boots the dump-capture kernel into single-user
479 dump. Hence generally it is useful either to build a UP dump-capture
480 kernel or specify maxcpus=1 option while loading dump-capture kernel.
484 * You should enable multi-cpu support in dump-capture kernel if you intend
485 to use multi-thread programs with it, such as parallel dump feature of
486 makedumpfile. Otherwise, the multi-thread program may have a great
487 performance degradation. To enable multi-cpu support, you should bring up an
488 SMP dump-capture kernel and specify maxcpus/nr_cpus, disable_cpu_apicid=[X]
508 After successfully loading the dump-capture kernel as previously
509 described, the system will reboot into the dump-capture kernel if a
511 die(), die_nmi() and in the sysrq handler (ALT-SysRq-c).
516 will boot into the dump-capture kernel ( die_nmi() ).
520 the system will boot into the dump-capture kernel.
522 On powerpc systems when a soft-reset is generated, die() is called by all cpus
523 and the system will boot into the dump-capture kernel.
525 For testing purposes, you can trigger a crash by using "ALT-SysRq-c",
526 "echo c > /proc/sysrq-trigger" or write a module to force the panic.
531 After the dump-capture kernel is booted, write out the dump file with
534 cp /proc/vmcore <dump-file>
538 scp /proc/vmcore remote_username@remote_ip:<dump-file>
543 makedumpfile -l --message-level 1 -d 31 /proc/vmcore <dump-file>
548 Before analyzing the dump image, you should reboot into a stable kernel.
551 /proc/vmcore. Use the debug vmlinux built with -g and run the following
554 gdb vmlinux <dump-file>
556 Stack trace for the task on processor 0, register display, and memory
561 ELF32-format headers using the --elf32-core-headers kernel option on the
567 https://github.com/crash-utility/crash
570 https://crash-utility.github.io/
586 This will cause a kdump to occur at the add_taint()->panic() call.
591 - kexec@lists.infradead.org