admin-guide/kdump/kdump.rst

2 Documentation for Kdump - The kexec-based Crash Dumping Solution
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
13 the system panics). The system kernel's memory image is preserved across
14 the reboot and is accessible to the dump-capture kernel.
18 a remote system.
23 When the system kernel boots, it reserves a small section of memory for
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
31 region just before rebooting into the dump-capture kernel.
42 All of the necessary information about the system kernel's core image is
45 passed to the dump-capture kernel through the elfcorehdr= boot
50 With the dump-capture kernel, you can access the memory image through
51 /proc/vmcore. This exports the dump as an ELF-format file that you can
61 Install kexec-tools
62 -------------------
66 2) Download the kexec-tools user-space package from the following URL:
68 http://kernel.org/pub/linux/utils/kernel/kexec/kexec-tools.tar.gz
72 The latest kexec-tools git tree is available at:
74 - git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
75 - http://www.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
78 http://www.kernel.org/git/?p=utils/kernel/kexec/kexec-tools.git
80 More information about kexec-tools can be found at
85 	tar xvpzf kexec-tools.tar.gz
87 4) Change to the kexec-tools directory, as follows::
89 	cd kexec-tools-VERSION
104 Build the system and dump-capture kernels
105 -----------------------------------------
108 1) Build a separate custom dump-capture kernel for capturing the
111 2) Or use the system kernel binary itself as dump-capture kernel and there is
112    no need to build a separate dump-capture kernel. This is possible
122 Following are the configuration setting required for system and
123 dump-capture kernels for enabling kdump support.
125 System kernel config options
126 ----------------------------
128 1) Enable "kexec system call" in "Processor type and features."::
132 2) Enable "sysfs file system support" in "Filesystem" -> "Pseudo
137    Note that "sysfs file system support" might not appear in the "Pseudo
152 Dump-capture kernel config options (Arch Independent)
153 -----------------------------------------------------
160 2) Enable "/proc/vmcore support" under "Filesystems" -> "Pseudo filesystems"::
166 Dump-capture kernel config options (Arch Dependent, i386 and x86_64)
167 --------------------------------------------------------------------
178 2) On i386 and x86_64, disable symmetric multi-processing support
184    when loading the dump-capture kernel, see section "Load the Dump-capture
201    kexec boot loader will load it in memory region reserved for dump-capture
206    start of memory region reserved for dump-capture kernel.
213 Dump-capture kernel config options (Arch Dependent, ppc64)
214 ----------------------------------------------------------
226 Dump-capture kernel config options (Arch Dependent, ia64)
227 ----------------------------------------------------------
229 - No specific options are required to create a dump-capture kernel
231   above. This means that it is possible to use the system kernel
232   as a dump-capture kernel if desired.
234   The crashkernel region can be automatically placed by the system
248 Dump-capture kernel config options (Arch Dependent, arm)
249 ----------------------------------------------------------
251 -   To use a relocatable kernel,
256 Dump-capture kernel config options (Arch Dependent, arm64)
257 ----------------------------------------------------------
259 - Please note that kvm of the dump-capture kernel will not be enabled
260   on non-VHE systems even if it is configured. This is because the CPU
268 on the value of System RAM -- that's mostly for distributors that pre-setup
269 the kernel command line to avoid a unbootable system after some memory has
275     range=start-[end]
279     crashkernel=512M-2G:64M,2G-:128M
290 Boot into System Kernel
296 2) Boot the system kernel with the boot parameter "crashkernel=Y@X",
297    where Y specifies how much memory to reserve for the dump-capture kernel
299    "crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory
300    starting at physical address 0x01000000 (16MB) for the dump-capture kernel.
308    dump-capture kernel config option notes above.
312    on the memory consumption of the kdump system. In general this is not
313    dependent on the memory size of the production system.
322 Load the Dump-capture Kernel
325 After booting to the system kernel, dump-capture kernel needs to be
330 of dump-capture kernel. Following is the summary.
334 	- Use vmlinux if kernel is not relocatable.
335 	- Use bzImage/vmlinuz if kernel is relocatable.
339 	- Use vmlinux
343 	- Use vmlinux or vmlinuz.gz
347 	- Use image or bzImage
351 	- Use zImage
355 	- Use vmlinux or Image
358 to load dump-capture kernel::
360    kexec -p <dump-capture-kernel-vmlinux-image> \
361    --initrd=<initrd-for-dump-capture-kernel> --args-linux \
362    --append="root=<root-dev> <arch-specific-options>"
365 to load dump-capture kernel::
367    kexec -p <dump-capture-kernel-bzImage> \
368    --initrd=<initrd-for-dump-capture-kernel> \
369    --append="root=<root-dev> <arch-specific-options>"
372 to load dump-capture kernel::
374    kexec --type zImage -p <dump-capture-kernel-bzImage> \
375    --initrd=<initrd-for-dump-capture-kernel> \
376    --dtb=<dtb-for-dump-capture-kernel> \
377    --append="root=<root-dev> <arch-specific-options>"
380 to load dump-capture kernel::
382    kexec -p <dump-capture-kernel-Image> \
383    --initrd=<initrd-for-dump-capture-kernel> \
384    --append="root=<root-dev> <arch-specific-options>"
386 Please note, that --args-linux does not need to be specified for ia64.
387 It is planned to make this a no-op on that architecture, but for now
391 loading dump-capture kernel.
413 Notes on loading the dump-capture kernel:
418   So, on non-PAE systems, ELF32 is always used.
420   The --elf32-core-headers option can be used to force the generation of ELF32
422   with ELF64 headers on 32-bit systems.
425   due to shared interrupts in the dump-capture kernel.
427 * You must specify <root-dev> in the format corresponding to the root
430 * Boot parameter "1" boots the dump-capture kernel into single-user
434   dump. Hence generally it is useful either to build a UP dump-capture
435   kernel or specify maxcpus=1 option while loading dump-capture kernel.
439 * You should enable multi-cpu support in dump-capture kernel if you intend
440   to use multi-thread programs with it, such as parallel dump feature of
441   makedumpfile. Otherwise, the multi-thread program may have a great
442   performance degradation. To enable multi-cpu support, you should bring up an
443   SMP dump-capture kernel and specify maxcpus/nr_cpus, disable_cpu_apicid=[X]
463 After successfully loading the dump-capture kernel as previously
464 described, the system will reboot into the dump-capture kernel if a
465 system crash is triggered.  Trigger points are located in panic(),
466 die(), die_nmi() and in the sysrq handler (ALT-SysRq-c).
470 If a hard lockup is detected and "NMI watchdog" is configured, the system
471 will boot into the dump-capture kernel ( die_nmi() ).
475 the system will boot into the dump-capture kernel.
477 On powerpc systems when a soft-reset is generated, die() is called by all cpus
478 and the system will boot into the dump-capture kernel.
480 For testing purposes, you can trigger a crash by using "ALT-SysRq-c",
481 "echo c > /proc/sysrq-trigger" or write a module to force the panic.
486 After the dump-capture kernel is booted, write out the dump file with
489    cp /proc/vmcore <dump-file>
498 /proc/vmcore. Use the debug vmlinux built with -g and run the following
501    gdb vmlinux <dump-file>
508 ELF32-format headers using the --elf32-core-headers kernel option on the
514    https://github.com/crash-utility/crash
517    https://crash-utility.github.io/
533 This will cause a kdump to occur at the add_taint()->panic() call.
538 - Vivek Goyal (vgoyal@redhat.com)
539 - Maneesh Soni (maneesh@in.ibm.com)