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David Wilderdc851a02006-06-25 05:47:55 -07001================================================================
2Documentation for Kdump - The kexec-based Crash Dumping Solution
Vivek Goyalb089f4a2005-06-25 14:58:15 -07003================================================================
4
David Wilderdc851a02006-06-25 05:47:55 -07005This document includes overview, setup and installation, and analysis
6information.
Vivek Goyalb089f4a2005-06-25 14:58:15 -07007
David Wilderdc851a02006-06-25 05:47:55 -07008Overview
9========
Vivek Goyalb089f4a2005-06-25 14:58:15 -070010
David Wilderdc851a02006-06-25 05:47:55 -070011Kdump uses kexec to quickly boot to a dump-capture kernel whenever a
12dump of the system kernel's memory needs to be taken (for example, when
13the system panics). The system kernel's memory image is preserved across
14the reboot and is accessible to the dump-capture kernel.
Vivek Goyalb089f4a2005-06-25 14:58:15 -070015
Pavel Machekf4e87572007-10-16 23:31:28 -070016You can use common commands, such as cp and scp, to copy the
David Wilderdc851a02006-06-25 05:47:55 -070017memory image to a dump file on the local disk, or across the network to
18a remote system.
Vivek Goyalb089f4a2005-06-25 14:58:15 -070019
Michael Holzheu91302142011-12-27 11:27:25 +010020Kdump and kexec are currently supported on the x86, x86_64, ppc64, ia64,
HuKeping16b03712014-08-29 15:19:11 -070021s390x and arm architectures.
Vivek Goyalb089f4a2005-06-25 14:58:15 -070022
David Wilderdc851a02006-06-25 05:47:55 -070023When the system kernel boots, it reserves a small section of memory for
24the dump-capture kernel. This ensures that ongoing Direct Memory Access
25(DMA) from the system kernel does not corrupt the dump-capture kernel.
26The kexec -p command loads the dump-capture kernel into this reserved
27memory.
Vivek Goyalb089f4a2005-06-25 14:58:15 -070028
David Wilderdc851a02006-06-25 05:47:55 -070029On x86 machines, the first 640 KB of physical memory is needed to boot,
30regardless of where the kernel loads. Therefore, kexec backs up this
31region just before rebooting into the dump-capture kernel.
Vivek Goyalb089f4a2005-06-25 14:58:15 -070032
Simon Horman30430132007-02-20 13:58:07 -080033Similarly on PPC64 machines first 32KB of physical memory is needed for
34booting regardless of where the kernel is loaded and to support 64K page
35size kexec backs up the first 64KB memory.
36
Michael Holzheu91302142011-12-27 11:27:25 +010037For s390x, when kdump is triggered, the crashkernel region is exchanged
38with the region [0, crashkernel region size] and then the kdump kernel
39runs in [0, crashkernel region size]. Therefore no relocatable kernel is
40needed for s390x.
41
David Wilderdc851a02006-06-25 05:47:55 -070042All of the necessary information about the system kernel's core image is
43encoded in the ELF format, and stored in a reserved area of memory
44before a crash. The physical address of the start of the ELF header is
45passed to the dump-capture kernel through the elfcorehdr= boot
Michael Holzheu91302142011-12-27 11:27:25 +010046parameter. Optionally the size of the ELF header can also be passed
47when using the elfcorehdr=[size[KMG]@]offset[KMG] syntax.
48
Vivek Goyalb089f4a2005-06-25 14:58:15 -070049
Zhang Yanfei987bf6f2013-07-03 15:08:38 -070050With 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
52write out using file copy commands such as cp or scp. Further, you can
53use analysis tools such as the GNU Debugger (GDB) and the Crash tool to
54debug the dump file. This method ensures that the dump pages are correctly
55ordered.
Vivek Goyalb089f4a2005-06-25 14:58:15 -070056
Vivek Goyalb089f4a2005-06-25 14:58:15 -070057
David Wilderdc851a02006-06-25 05:47:55 -070058Setup and Installation
59======================
Vivek Goyalb089f4a2005-06-25 14:58:15 -070060
Vivek Goyal9c61a442007-01-10 23:15:35 -080061Install kexec-tools
62-------------------
Vivek Goyalb089f4a2005-06-25 14:58:15 -070063
David Wilderdc851a02006-06-25 05:47:55 -0700641) Login as the root user.
Vivek Goyalb089f4a2005-06-25 14:58:15 -070065
David Wilderdc851a02006-06-25 05:47:55 -0700662) Download the kexec-tools user-space package from the following URL:
Vivek Goyalb089f4a2005-06-25 14:58:15 -070067
Simon Hormandb6857c2010-11-25 10:30:12 +090068http://kernel.org/pub/linux/utils/kernel/kexec/kexec-tools.tar.gz
Hormsea112bd2007-01-22 20:40:48 -080069
Simon Hormand84a52f2008-07-28 15:46:34 -070070This is a symlink to the latest version.
Vivek Goyal9c61a442007-01-10 23:15:35 -080071
Simon Hormand84a52f2008-07-28 15:46:34 -070072The latest kexec-tools git tree is available at:
Vivek Goyal9c61a442007-01-10 23:15:35 -080073
Simon Hormandb6857c2010-11-25 10:30:12 +090074git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
75and
76http://www.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
77
78There is also a gitweb interface available at
79http://www.kernel.org/git/?p=utils/kernel/kexec/kexec-tools.git
Simon Hormand84a52f2008-07-28 15:46:34 -070080
81More information about kexec-tools can be found at
Olaf Heringb1bdd2e2012-07-18 14:12:04 -070082http://horms.net/projects/kexec/
Vivek Goyalb089f4a2005-06-25 14:58:15 -070083
David Wilderdc851a02006-06-25 05:47:55 -0700843) Unpack the tarball with the tar command, as follows:
85
Simon Hormand84a52f2008-07-28 15:46:34 -070086 tar xvpzf kexec-tools.tar.gz
David Wilderdc851a02006-06-25 05:47:55 -070087
Hormsea112bd2007-01-22 20:40:48 -0800884) Change to the kexec-tools directory, as follows:
David Wilderdc851a02006-06-25 05:47:55 -070089
Simon Hormand84a52f2008-07-28 15:46:34 -070090 cd kexec-tools-VERSION
David Wilderdc851a02006-06-25 05:47:55 -070091
Vivek Goyal9c61a442007-01-10 23:15:35 -0800925) Configure the package, as follows:
David Wilderdc851a02006-06-25 05:47:55 -070093
94 ./configure
95
Vivek Goyal9c61a442007-01-10 23:15:35 -0800966) Compile the package, as follows:
David Wilderdc851a02006-06-25 05:47:55 -070097
98 make
99
Vivek Goyal9c61a442007-01-10 23:15:35 -08001007) Install the package, as follows:
David Wilderdc851a02006-06-25 05:47:55 -0700101
102 make install
103
104
Vivek Goyal9c61a442007-01-10 23:15:35 -0800105Build the system and dump-capture kernels
106-----------------------------------------
107There are two possible methods of using Kdump.
David Wilderdc851a02006-06-25 05:47:55 -0700108
Vivek Goyal9c61a442007-01-10 23:15:35 -08001091) Build a separate custom dump-capture kernel for capturing the
110 kernel core dump.
David Wilderdc851a02006-06-25 05:47:55 -0700111
Vivek Goyal9c61a442007-01-10 23:15:35 -08001122) Or use the system kernel binary itself as dump-capture kernel and there is
113 no need to build a separate dump-capture kernel. This is possible
Matt LaPlante19f59462009-04-27 15:06:31 +0200114 only with the architectures which support a relocatable kernel. As
HuKeping16b03712014-08-29 15:19:11 -0700115 of today, i386, x86_64, ppc64, ia64 and arm architectures support relocatable
Mohan Kumar M54622f12008-10-21 17:38:10 +0000116 kernel.
Vivek Goyal9c61a442007-01-10 23:15:35 -0800117
118Building a relocatable kernel is advantageous from the point of view that
119one does not have to build a second kernel for capturing the dump. But
120at the same time one might want to build a custom dump capture kernel
121suitable to his needs.
122
123Following are the configuration setting required for system and
124dump-capture kernels for enabling kdump support.
125
126System kernel config options
127----------------------------
David Wilderdc851a02006-06-25 05:47:55 -0700128
1291) Enable "kexec system call" in "Processor type and features."
130
131 CONFIG_KEXEC=y
132
1332) Enable "sysfs file system support" in "Filesystem" -> "Pseudo
134 filesystems." This is usually enabled by default.
135
136 CONFIG_SYSFS=y
137
138 Note that "sysfs file system support" might not appear in the "Pseudo
139 filesystems" menu if "Configure standard kernel features (for small
140 systems)" is not enabled in "General Setup." In this case, check the
141 .config file itself to ensure that sysfs is turned on, as follows:
142
143 grep 'CONFIG_SYSFS' .config
144
1453) Enable "Compile the kernel with debug info" in "Kernel hacking."
146
147 CONFIG_DEBUG_INFO=Y
148
149 This causes the kernel to be built with debug symbols. The dump
150 analysis tools require a vmlinux with debug symbols in order to read
151 and analyze a dump file.
152
Vivek Goyal9c61a442007-01-10 23:15:35 -0800153Dump-capture kernel config options (Arch Independent)
154-----------------------------------------------------
David Wilderdc851a02006-06-25 05:47:55 -0700155
Vivek Goyal9c61a442007-01-10 23:15:35 -08001561) Enable "kernel crash dumps" support under "Processor type and
157 features":
David Wilderdc851a02006-06-25 05:47:55 -0700158
Vivek Goyal9c61a442007-01-10 23:15:35 -0800159 CONFIG_CRASH_DUMP=y
David Wilderdc851a02006-06-25 05:47:55 -0700160
Vivek Goyal9c61a442007-01-10 23:15:35 -08001612) Enable "/proc/vmcore support" under "Filesystems" -> "Pseudo filesystems".
David Wilderdc851a02006-06-25 05:47:55 -0700162
Vivek Goyal9c61a442007-01-10 23:15:35 -0800163 CONFIG_PROC_VMCORE=y
164 (CONFIG_PROC_VMCORE is set by default when CONFIG_CRASH_DUMP is selected.)
David Wilderdc851a02006-06-25 05:47:55 -0700165
Bernhard Walle8bc9d422007-10-16 23:31:21 -0700166Dump-capture kernel config options (Arch Dependent, i386 and x86_64)
167--------------------------------------------------------------------
168
1691) On i386, enable high memory support under "Processor type and
David Wilderdc851a02006-06-25 05:47:55 -0700170 features":
171
172 CONFIG_HIGHMEM64G=y
173 or
174 CONFIG_HIGHMEM4G
175
Bernhard Walle8bc9d422007-10-16 23:31:21 -07001762) On i386 and x86_64, disable symmetric multi-processing support
David Wilderdc851a02006-06-25 05:47:55 -0700177 under "Processor type and features":
178
179 CONFIG_SMP=n
Vivek Goyal9c61a442007-01-10 23:15:35 -0800180
David Wilderdc851a02006-06-25 05:47:55 -0700181 (If CONFIG_SMP=y, then specify maxcpus=1 on the kernel command line
182 when loading the dump-capture kernel, see section "Load the Dump-capture
183 Kernel".)
184
Vivek Goyal9c61a442007-01-10 23:15:35 -08001853) If one wants to build and use a relocatable kernel,
186 Enable "Build a relocatable kernel" support under "Processor type and
187 features"
David Wilderdc851a02006-06-25 05:47:55 -0700188
Vivek Goyal9c61a442007-01-10 23:15:35 -0800189 CONFIG_RELOCATABLE=y
David Wilderdc851a02006-06-25 05:47:55 -0700190
Vivek Goyal9c61a442007-01-10 23:15:35 -08001914) Use a suitable value for "Physical address where the kernel is
192 loaded" (under "Processor type and features"). This only appears when
193 "kernel crash dumps" is enabled. A suitable value depends upon
194 whether kernel is relocatable or not.
David Wilderdc851a02006-06-25 05:47:55 -0700195
Vivek Goyal9c61a442007-01-10 23:15:35 -0800196 If you are using a relocatable kernel use CONFIG_PHYSICAL_START=0x100000
197 This will compile the kernel for physical address 1MB, but given the fact
198 kernel is relocatable, it can be run from any physical address hence
199 kexec boot loader will load it in memory region reserved for dump-capture
200 kernel.
David Wilderdc851a02006-06-25 05:47:55 -0700201
Vivek Goyal9c61a442007-01-10 23:15:35 -0800202 Otherwise it should be the start of memory region reserved for
203 second kernel using boot parameter "crashkernel=Y@X". Here X is
204 start of memory region reserved for dump-capture kernel.
205 Generally X is 16MB (0x1000000). So you can set
206 CONFIG_PHYSICAL_START=0x1000000
207
2085) Make and install the kernel and its modules. DO NOT add this kernel
209 to the boot loader configuration files.
210
Vivek Goyal9c61a442007-01-10 23:15:35 -0800211Dump-capture kernel config options (Arch Dependent, ppc64)
212----------------------------------------------------------
213
Mohan Kumar M54622f12008-10-21 17:38:10 +00002141) Enable "Build a kdump crash kernel" support under "Kernel" options:
215
216 CONFIG_CRASH_DUMP=y
217
2182) Enable "Build a relocatable kernel" support
219
220 CONFIG_RELOCATABLE=y
221
222 Make and install the kernel and its modules.
Vivek Goyal9c61a442007-01-10 23:15:35 -0800223
224Dump-capture kernel config options (Arch Dependent, ia64)
225----------------------------------------------------------
Hormsee8bb9e2007-01-22 20:40:49 -0800226
227- No specific options are required to create a dump-capture kernel
Matt LaPlante19f59462009-04-27 15:06:31 +0200228 for ia64, other than those specified in the arch independent section
Hormsee8bb9e2007-01-22 20:40:49 -0800229 above. This means that it is possible to use the system kernel
230 as a dump-capture kernel if desired.
231
232 The crashkernel region can be automatically placed by the system
233 kernel at run time. This is done by specifying the base address as 0,
234 or omitting it all together.
235
236 crashkernel=256M@0
237 or
238 crashkernel=256M
239
240 If the start address is specified, note that the start address of the
241 kernel will be aligned to 64Mb, so if the start address is not then
242 any space below the alignment point will be wasted.
Vivek Goyal9c61a442007-01-10 23:15:35 -0800243
HuKeping16b03712014-08-29 15:19:11 -0700244Dump-capture kernel config options (Arch Dependent, arm)
245----------------------------------------------------------
246
247- To use a relocatable kernel,
248 Enable "AUTO_ZRELADDR" support under "Boot" options:
249
250 AUTO_ZRELADDR=y
Vivek Goyal9c61a442007-01-10 23:15:35 -0800251
Bernhard Wallefb391592007-10-18 23:41:02 -0700252Extended crashkernel syntax
253===========================
254
255While the "crashkernel=size[@offset]" syntax is sufficient for most
256configurations, sometimes it's handy to have the reserved memory dependent
257on the value of System RAM -- that's mostly for distributors that pre-setup
258the kernel command line to avoid a unbootable system after some memory has
259been removed from the machine.
260
261The syntax is:
262
263 crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
264 range=start-[end]
265
266For example:
267
268 crashkernel=512M-2G:64M,2G-:128M
269
270This would mean:
271
272 1) if the RAM is smaller than 512M, then don't reserve anything
273 (this is the "rescue" case)
Michael Ellermanbe089d792008-05-01 04:34:49 -0700274 2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
Bernhard Wallefb391592007-10-18 23:41:02 -0700275 3) if the RAM size is larger than 2G, then reserve 128M
276
277
Michael Ellermanbe089d792008-05-01 04:34:49 -0700278
Vivek Goyal9c61a442007-01-10 23:15:35 -0800279Boot into System Kernel
280=======================
281
Simon Horman30430132007-02-20 13:58:07 -08002821) Update the boot loader (such as grub, yaboot, or lilo) configuration
283 files as necessary.
Vivek Goyal9c61a442007-01-10 23:15:35 -0800284
2852) Boot the system kernel with the boot parameter "crashkernel=Y@X",
286 where Y specifies how much memory to reserve for the dump-capture kernel
287 and X specifies the beginning of this reserved memory. For example,
288 "crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory
289 starting at physical address 0x01000000 (16MB) for the dump-capture kernel.
290
291 On x86 and x86_64, use "crashkernel=64M@16M".
292
293 On ppc64, use "crashkernel=128M@32M".
David Wilderdc851a02006-06-25 05:47:55 -0700294
Hormsee8bb9e2007-01-22 20:40:49 -0800295 On ia64, 256M@256M is a generous value that typically works.
296 The region may be automatically placed on ia64, see the
297 dump-capture kernel config option notes above.
Xishi Qiu797f6a62013-03-25 19:14:16 +0800298 If use sparse memory, the size should be rounded to GRANULE boundaries.
Hormsee8bb9e2007-01-22 20:40:49 -0800299
Michael Holzheu91302142011-12-27 11:27:25 +0100300 On s390x, typically use "crashkernel=xxM". The value of xx is dependent
301 on the memory consumption of the kdump system. In general this is not
302 dependent on the memory size of the production system.
303
Russell King61603012016-03-14 19:34:37 +0000304 On arm, the use of "crashkernel=Y@X" is no longer necessary; the
305 kernel will automatically locate the crash kernel image within the
306 first 512MB of RAM if X is not given.
HuKeping16b03712014-08-29 15:19:11 -0700307
308
David Wilderdc851a02006-06-25 05:47:55 -0700309Load the Dump-capture Kernel
310============================
311
Vivek Goyal9c61a442007-01-10 23:15:35 -0800312After booting to the system kernel, dump-capture kernel needs to be
313loaded.
David Wilderdc851a02006-06-25 05:47:55 -0700314
Vivek Goyal9c61a442007-01-10 23:15:35 -0800315Based on the architecture and type of image (relocatable or not), one
316can choose to load the uncompressed vmlinux or compressed bzImage/vmlinuz
317of dump-capture kernel. Following is the summary.
318
Bernhard Walle8bc9d422007-10-16 23:31:21 -0700319For i386 and x86_64:
Vivek Goyal9c61a442007-01-10 23:15:35 -0800320 - Use vmlinux if kernel is not relocatable.
321 - Use bzImage/vmlinuz if kernel is relocatable.
Vivek Goyal9c61a442007-01-10 23:15:35 -0800322For ppc64:
323 - Use vmlinux
324For ia64:
Hormsee8bb9e2007-01-22 20:40:49 -0800325 - Use vmlinux or vmlinuz.gz
Michael Holzheu91302142011-12-27 11:27:25 +0100326For s390x:
327 - Use image or bzImage
HuKeping16b03712014-08-29 15:19:11 -0700328For arm:
329 - Use zImage
Vivek Goyal9c61a442007-01-10 23:15:35 -0800330
331If you are using a uncompressed vmlinux image then use following command
332to load dump-capture kernel.
333
334 kexec -p <dump-capture-kernel-vmlinux-image> \
David Wilderdc851a02006-06-25 05:47:55 -0700335 --initrd=<initrd-for-dump-capture-kernel> --args-linux \
Vivek Goyal9c61a442007-01-10 23:15:35 -0800336 --append="root=<root-dev> <arch-specific-options>"
337
338If you are using a compressed bzImage/vmlinuz, then use following command
339to load dump-capture kernel.
340
341 kexec -p <dump-capture-kernel-bzImage> \
342 --initrd=<initrd-for-dump-capture-kernel> \
343 --append="root=<root-dev> <arch-specific-options>"
344
HuKeping16b03712014-08-29 15:19:11 -0700345If you are using a compressed zImage, then use following command
346to load dump-capture kernel.
347
348 kexec --type zImage -p <dump-capture-kernel-bzImage> \
349 --initrd=<initrd-for-dump-capture-kernel> \
350 --dtb=<dtb-for-dump-capture-kernel> \
351 --append="root=<root-dev> <arch-specific-options>"
352
353
Hormsee8bb9e2007-01-22 20:40:49 -0800354Please note, that --args-linux does not need to be specified for ia64.
355It is planned to make this a no-op on that architecture, but for now
356it should be omitted
357
Vivek Goyal9c61a442007-01-10 23:15:35 -0800358Following are the arch specific command line options to be used while
359loading dump-capture kernel.
360
Hormsee8bb9e2007-01-22 20:40:49 -0800361For i386, x86_64 and ia64:
Bernhard Walleac984ab2007-10-16 23:31:23 -0700362 "1 irqpoll maxcpus=1 reset_devices"
Vivek Goyal9c61a442007-01-10 23:15:35 -0800363
364For ppc64:
Bernhard Walleac984ab2007-10-16 23:31:23 -0700365 "1 maxcpus=1 noirqdistrib reset_devices"
Vivek Goyal9c61a442007-01-10 23:15:35 -0800366
Michael Holzheu91302142011-12-27 11:27:25 +0100367For s390x:
368 "1 maxcpus=1 cgroup_disable=memory"
David Wilderdc851a02006-06-25 05:47:55 -0700369
HuKeping16b03712014-08-29 15:19:11 -0700370For arm:
371 "1 maxcpus=1 reset_devices"
372
David Wilderdc851a02006-06-25 05:47:55 -0700373Notes on loading the dump-capture kernel:
374
David Wilderdc851a02006-06-25 05:47:55 -0700375* By default, the ELF headers are stored in ELF64 format to support
Bernhard Walle4fd45092007-10-16 23:31:22 -0700376 systems with more than 4GB memory. On i386, kexec automatically checks if
377 the physical RAM size exceeds the 4 GB limit and if not, uses ELF32.
378 So, on non-PAE systems, ELF32 is always used.
379
380 The --elf32-core-headers option can be used to force the generation of ELF32
381 headers. This is necessary because GDB currently cannot open vmcore files
382 with ELF64 headers on 32-bit systems.
David Wilderdc851a02006-06-25 05:47:55 -0700383
384* The "irqpoll" boot parameter reduces driver initialization failures
385 due to shared interrupts in the dump-capture kernel.
386
387* You must specify <root-dev> in the format corresponding to the root
388 device name in the output of mount command.
389
Horms473e66f2007-02-12 00:52:18 -0800390* Boot parameter "1" boots the dump-capture kernel into single-user
391 mode without networking. If you want networking, use "3".
David Wilderdc851a02006-06-25 05:47:55 -0700392
Vivek Goyal9c61a442007-01-10 23:15:35 -0800393* We generally don' have to bring up a SMP kernel just to capture the
394 dump. Hence generally it is useful either to build a UP dump-capture
395 kernel or specify maxcpus=1 option while loading dump-capture kernel.
David Wilderdc851a02006-06-25 05:47:55 -0700396
Michael Holzheu91302142011-12-27 11:27:25 +0100397* For s390x there are two kdump modes: If a ELF header is specified with
398 the elfcorehdr= kernel parameter, it is used by the kdump kernel as it
399 is done on all other architectures. If no elfcorehdr= kernel parameter is
400 specified, the s390x kdump kernel dynamically creates the header. The
401 second mode has the advantage that for CPU and memory hotplug, kdump has
402 not to be reloaded with kexec_load().
403
404* For s390x systems with many attached devices the "cio_ignore" kernel
405 parameter should be used for the kdump kernel in order to prevent allocation
406 of kernel memory for devices that are not relevant for kdump. The same
407 applies to systems that use SCSI/FCP devices. In that case the
408 "allow_lun_scan" zfcp module parameter should be set to zero before
409 setting FCP devices online.
410
David Wilderdc851a02006-06-25 05:47:55 -0700411Kernel Panic
412============
413
414After successfully loading the dump-capture kernel as previously
415described, the system will reboot into the dump-capture kernel if a
416system crash is triggered. Trigger points are located in panic(),
417die(), die_nmi() and in the sysrq handler (ALT-SysRq-c).
418
419The following conditions will execute a crash trigger point:
420
421If a hard lockup is detected and "NMI watchdog" is configured, the system
422will boot into the dump-capture kernel ( die_nmi() ).
423
424If die() is called, and it happens to be a thread with pid 0 or 1, or die()
425is called inside interrupt context or die() is called and panic_on_oops is set,
426the system will boot into the dump-capture kernel.
427
Pavel Machekf4e87572007-10-16 23:31:28 -0700428On powerpc systems when a soft-reset is generated, die() is called by all cpus
Simon Horman30430132007-02-20 13:58:07 -0800429and the system will boot into the dump-capture kernel.
David Wilderdc851a02006-06-25 05:47:55 -0700430
431For testing purposes, you can trigger a crash by using "ALT-SysRq-c",
Simon Horman30430132007-02-20 13:58:07 -0800432"echo c > /proc/sysrq-trigger" or write a module to force the panic.
David Wilderdc851a02006-06-25 05:47:55 -0700433
434Write Out the Dump File
435=======================
436
437After the dump-capture kernel is booted, write out the dump file with
438the following command:
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700439
440 cp /proc/vmcore <dump-file>
441
Maneesh Sonia7e670d2006-01-09 20:51:53 -0800442
David Wilderdc851a02006-06-25 05:47:55 -0700443Analysis
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700444========
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700445
David Wilderdc851a02006-06-25 05:47:55 -0700446Before analyzing the dump image, you should reboot into a stable kernel.
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700447
David Wilderdc851a02006-06-25 05:47:55 -0700448You can do limited analysis using GDB on the dump file copied out of
449/proc/vmcore. Use the debug vmlinux built with -g and run the following
450command:
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700451
David Wilderdc851a02006-06-25 05:47:55 -0700452 gdb vmlinux <dump-file>
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700453
David Wilderdc851a02006-06-25 05:47:55 -0700454Stack trace for the task on processor 0, register display, and memory
455display work fine.
456
457Note: GDB cannot analyze core files generated in ELF64 format for x86.
458On systems with a maximum of 4GB of memory, you can generate
459ELF32-format headers using the --elf32-core-headers kernel option on the
460dump kernel.
461
462You can also use the Crash utility to analyze dump files in Kdump
463format. Crash is available on Dave Anderson's site at the following URL:
464
465 http://people.redhat.com/~anderson/
Maneesh Sonia7e670d2006-01-09 20:51:53 -0800466
Prarit Bhargava9e3961a2014-12-10 15:45:50 -0800467Trigger Kdump on WARN()
468=======================
469
470The kernel parameter, panic_on_warn, calls panic() in all WARN() paths. This
471will cause a kdump to occur at the panic() call. In cases where a user wants
472to specify this during runtime, /proc/sys/kernel/panic_on_warn can be set to 1
473to achieve the same behaviour.
Maneesh Sonia7e670d2006-01-09 20:51:53 -0800474
David Wilderdc851a02006-06-25 05:47:55 -0700475Contact
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700476=======
David Wilderdc851a02006-06-25 05:47:55 -0700477
Simon Hormandb6857c2010-11-25 10:30:12 +0900478Vivek Goyal (vgoyal@redhat.com)
Vivek Goyald58831e2005-06-25 14:58:17 -0700479Maneesh Soni (maneesh@in.ibm.com)
David Wilderdc851a02006-06-25 05:47:55 -0700480