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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,
21and s390x 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
David Wilderdc851a02006-06-25 05:47:55 -070050With the dump-capture kernel, you can access the memory image, or "old
51memory," in two ways:
Vivek Goyalb089f4a2005-06-25 14:58:15 -070052
David Wilderdc851a02006-06-25 05:47:55 -070053- Through a /dev/oldmem device interface. A capture utility can read the
54 device file and write out the memory in raw format. This is a raw dump
55 of memory. Analysis and capture tools must be intelligent enough to
56 determine where to look for the right information.
Vivek Goyalb089f4a2005-06-25 14:58:15 -070057
David Wilderdc851a02006-06-25 05:47:55 -070058- Through /proc/vmcore. This exports the dump as an ELF-format file that
59 you can write out using file copy commands such as cp or scp. Further,
60 you can use analysis tools such as the GNU Debugger (GDB) and the Crash
61 tool to debug the dump file. This method ensures that the dump pages are
62 correctly ordered.
Vivek Goyalb089f4a2005-06-25 14:58:15 -070063
Vivek Goyalb089f4a2005-06-25 14:58:15 -070064
David Wilderdc851a02006-06-25 05:47:55 -070065Setup and Installation
66======================
Vivek Goyalb089f4a2005-06-25 14:58:15 -070067
Vivek Goyal9c61a442007-01-10 23:15:35 -080068Install kexec-tools
69-------------------
Vivek Goyalb089f4a2005-06-25 14:58:15 -070070
David Wilderdc851a02006-06-25 05:47:55 -0700711) Login as the root user.
Vivek Goyalb089f4a2005-06-25 14:58:15 -070072
David Wilderdc851a02006-06-25 05:47:55 -0700732) Download the kexec-tools user-space package from the following URL:
Vivek Goyalb089f4a2005-06-25 14:58:15 -070074
Simon Hormandb6857c2010-11-25 10:30:12 +090075http://kernel.org/pub/linux/utils/kernel/kexec/kexec-tools.tar.gz
Hormsea112bd2007-01-22 20:40:48 -080076
Simon Hormand84a52f2008-07-28 15:46:34 -070077This is a symlink to the latest version.
Vivek Goyal9c61a442007-01-10 23:15:35 -080078
Simon Hormand84a52f2008-07-28 15:46:34 -070079The latest kexec-tools git tree is available at:
Vivek Goyal9c61a442007-01-10 23:15:35 -080080
Simon Hormandb6857c2010-11-25 10:30:12 +090081git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
82and
83http://www.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
84
85There is also a gitweb interface available at
86http://www.kernel.org/git/?p=utils/kernel/kexec/kexec-tools.git
Simon Hormand84a52f2008-07-28 15:46:34 -070087
88More information about kexec-tools can be found at
Olaf Heringb1bdd2e2012-07-18 14:12:04 -070089http://horms.net/projects/kexec/
Vivek Goyalb089f4a2005-06-25 14:58:15 -070090
David Wilderdc851a02006-06-25 05:47:55 -0700913) Unpack the tarball with the tar command, as follows:
92
Simon Hormand84a52f2008-07-28 15:46:34 -070093 tar xvpzf kexec-tools.tar.gz
David Wilderdc851a02006-06-25 05:47:55 -070094
Hormsea112bd2007-01-22 20:40:48 -0800954) Change to the kexec-tools directory, as follows:
David Wilderdc851a02006-06-25 05:47:55 -070096
Simon Hormand84a52f2008-07-28 15:46:34 -070097 cd kexec-tools-VERSION
David Wilderdc851a02006-06-25 05:47:55 -070098
Vivek Goyal9c61a442007-01-10 23:15:35 -0800995) Configure the package, as follows:
David Wilderdc851a02006-06-25 05:47:55 -0700100
101 ./configure
102
Vivek Goyal9c61a442007-01-10 23:15:35 -08001036) Compile the package, as follows:
David Wilderdc851a02006-06-25 05:47:55 -0700104
105 make
106
Vivek Goyal9c61a442007-01-10 23:15:35 -08001077) Install the package, as follows:
David Wilderdc851a02006-06-25 05:47:55 -0700108
109 make install
110
111
Vivek Goyal9c61a442007-01-10 23:15:35 -0800112Build the system and dump-capture kernels
113-----------------------------------------
114There are two possible methods of using Kdump.
David Wilderdc851a02006-06-25 05:47:55 -0700115
Vivek Goyal9c61a442007-01-10 23:15:35 -08001161) Build a separate custom dump-capture kernel for capturing the
117 kernel core dump.
David Wilderdc851a02006-06-25 05:47:55 -0700118
Vivek Goyal9c61a442007-01-10 23:15:35 -08001192) Or use the system kernel binary itself as dump-capture kernel and there is
120 no need to build a separate dump-capture kernel. This is possible
Matt LaPlante19f59462009-04-27 15:06:31 +0200121 only with the architectures which support a relocatable kernel. As
Mohan Kumar M54622f12008-10-21 17:38:10 +0000122 of today, i386, x86_64, ppc64 and ia64 architectures support relocatable
123 kernel.
Vivek Goyal9c61a442007-01-10 23:15:35 -0800124
125Building a relocatable kernel is advantageous from the point of view that
126one does not have to build a second kernel for capturing the dump. But
127at the same time one might want to build a custom dump capture kernel
128suitable to his needs.
129
130Following are the configuration setting required for system and
131dump-capture kernels for enabling kdump support.
132
133System kernel config options
134----------------------------
David Wilderdc851a02006-06-25 05:47:55 -0700135
1361) Enable "kexec system call" in "Processor type and features."
137
138 CONFIG_KEXEC=y
139
1402) Enable "sysfs file system support" in "Filesystem" -> "Pseudo
141 filesystems." This is usually enabled by default.
142
143 CONFIG_SYSFS=y
144
145 Note that "sysfs file system support" might not appear in the "Pseudo
146 filesystems" menu if "Configure standard kernel features (for small
147 systems)" is not enabled in "General Setup." In this case, check the
148 .config file itself to ensure that sysfs is turned on, as follows:
149
150 grep 'CONFIG_SYSFS' .config
151
1523) Enable "Compile the kernel with debug info" in "Kernel hacking."
153
154 CONFIG_DEBUG_INFO=Y
155
156 This causes the kernel to be built with debug symbols. The dump
157 analysis tools require a vmlinux with debug symbols in order to read
158 and analyze a dump file.
159
Vivek Goyal9c61a442007-01-10 23:15:35 -0800160Dump-capture kernel config options (Arch Independent)
161-----------------------------------------------------
David Wilderdc851a02006-06-25 05:47:55 -0700162
Vivek Goyal9c61a442007-01-10 23:15:35 -08001631) Enable "kernel crash dumps" support under "Processor type and
164 features":
David Wilderdc851a02006-06-25 05:47:55 -0700165
Vivek Goyal9c61a442007-01-10 23:15:35 -0800166 CONFIG_CRASH_DUMP=y
David Wilderdc851a02006-06-25 05:47:55 -0700167
Vivek Goyal9c61a442007-01-10 23:15:35 -08001682) Enable "/proc/vmcore support" under "Filesystems" -> "Pseudo filesystems".
David Wilderdc851a02006-06-25 05:47:55 -0700169
Vivek Goyal9c61a442007-01-10 23:15:35 -0800170 CONFIG_PROC_VMCORE=y
171 (CONFIG_PROC_VMCORE is set by default when CONFIG_CRASH_DUMP is selected.)
David Wilderdc851a02006-06-25 05:47:55 -0700172
Bernhard Walle8bc9d422007-10-16 23:31:21 -0700173Dump-capture kernel config options (Arch Dependent, i386 and x86_64)
174--------------------------------------------------------------------
175
1761) On i386, enable high memory support under "Processor type and
David Wilderdc851a02006-06-25 05:47:55 -0700177 features":
178
179 CONFIG_HIGHMEM64G=y
180 or
181 CONFIG_HIGHMEM4G
182
Bernhard Walle8bc9d422007-10-16 23:31:21 -07001832) On i386 and x86_64, disable symmetric multi-processing support
David Wilderdc851a02006-06-25 05:47:55 -0700184 under "Processor type and features":
185
186 CONFIG_SMP=n
Vivek Goyal9c61a442007-01-10 23:15:35 -0800187
David Wilderdc851a02006-06-25 05:47:55 -0700188 (If CONFIG_SMP=y, then specify maxcpus=1 on the kernel command line
189 when loading the dump-capture kernel, see section "Load the Dump-capture
190 Kernel".)
191
Vivek Goyal9c61a442007-01-10 23:15:35 -08001923) If one wants to build and use a relocatable kernel,
193 Enable "Build a relocatable kernel" support under "Processor type and
194 features"
David Wilderdc851a02006-06-25 05:47:55 -0700195
Vivek Goyal9c61a442007-01-10 23:15:35 -0800196 CONFIG_RELOCATABLE=y
David Wilderdc851a02006-06-25 05:47:55 -0700197
Vivek Goyal9c61a442007-01-10 23:15:35 -08001984) Use a suitable value for "Physical address where the kernel is
199 loaded" (under "Processor type and features"). This only appears when
200 "kernel crash dumps" is enabled. A suitable value depends upon
201 whether kernel is relocatable or not.
David Wilderdc851a02006-06-25 05:47:55 -0700202
Vivek Goyal9c61a442007-01-10 23:15:35 -0800203 If you are using a relocatable kernel use CONFIG_PHYSICAL_START=0x100000
204 This will compile the kernel for physical address 1MB, but given the fact
205 kernel is relocatable, it can be run from any physical address hence
206 kexec boot loader will load it in memory region reserved for dump-capture
207 kernel.
David Wilderdc851a02006-06-25 05:47:55 -0700208
Vivek Goyal9c61a442007-01-10 23:15:35 -0800209 Otherwise it should be the start of memory region reserved for
210 second kernel using boot parameter "crashkernel=Y@X". Here X is
211 start of memory region reserved for dump-capture kernel.
212 Generally X is 16MB (0x1000000). So you can set
213 CONFIG_PHYSICAL_START=0x1000000
214
2155) Make and install the kernel and its modules. DO NOT add this kernel
216 to the boot loader configuration files.
217
Vivek Goyal9c61a442007-01-10 23:15:35 -0800218Dump-capture kernel config options (Arch Dependent, ppc64)
219----------------------------------------------------------
220
Mohan Kumar M54622f12008-10-21 17:38:10 +00002211) Enable "Build a kdump crash kernel" support under "Kernel" options:
222
223 CONFIG_CRASH_DUMP=y
224
2252) Enable "Build a relocatable kernel" support
226
227 CONFIG_RELOCATABLE=y
228
229 Make and install the kernel and its modules.
Vivek Goyal9c61a442007-01-10 23:15:35 -0800230
231Dump-capture kernel config options (Arch Dependent, ia64)
232----------------------------------------------------------
Hormsee8bb9e2007-01-22 20:40:49 -0800233
234- No specific options are required to create a dump-capture kernel
Matt LaPlante19f59462009-04-27 15:06:31 +0200235 for ia64, other than those specified in the arch independent section
Hormsee8bb9e2007-01-22 20:40:49 -0800236 above. This means that it is possible to use the system kernel
237 as a dump-capture kernel if desired.
238
239 The crashkernel region can be automatically placed by the system
240 kernel at run time. This is done by specifying the base address as 0,
241 or omitting it all together.
242
243 crashkernel=256M@0
244 or
245 crashkernel=256M
246
247 If the start address is specified, note that the start address of the
248 kernel will be aligned to 64Mb, so if the start address is not then
249 any space below the alignment point will be wasted.
Vivek Goyal9c61a442007-01-10 23:15:35 -0800250
251
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
Michael Ellermanbe089d792008-05-01 04:34:49 -0700266 'start' is inclusive and 'end' is exclusive.
267
Bernhard Wallefb391592007-10-18 23:41:02 -0700268For example:
269
270 crashkernel=512M-2G:64M,2G-:128M
271
272This would mean:
273
274 1) if the RAM is smaller than 512M, then don't reserve anything
275 (this is the "rescue" case)
Michael Ellermanbe089d792008-05-01 04:34:49 -0700276 2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
Bernhard Wallefb391592007-10-18 23:41:02 -0700277 3) if the RAM size is larger than 2G, then reserve 128M
278
279
Michael Ellermanbe089d792008-05-01 04:34:49 -0700280
Vivek Goyal9c61a442007-01-10 23:15:35 -0800281Boot into System Kernel
282=======================
283
Simon Horman30430132007-02-20 13:58:07 -08002841) Update the boot loader (such as grub, yaboot, or lilo) configuration
285 files as necessary.
Vivek Goyal9c61a442007-01-10 23:15:35 -0800286
2872) Boot the system kernel with the boot parameter "crashkernel=Y@X",
288 where Y specifies how much memory to reserve for the dump-capture kernel
289 and X specifies the beginning of this reserved memory. For example,
290 "crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory
291 starting at physical address 0x01000000 (16MB) for the dump-capture kernel.
292
293 On x86 and x86_64, use "crashkernel=64M@16M".
294
295 On ppc64, use "crashkernel=128M@32M".
David Wilderdc851a02006-06-25 05:47:55 -0700296
Hormsee8bb9e2007-01-22 20:40:49 -0800297 On ia64, 256M@256M is a generous value that typically works.
298 The region may be automatically placed on ia64, see the
299 dump-capture kernel config option notes above.
300
Michael Holzheu91302142011-12-27 11:27:25 +0100301 On s390x, typically use "crashkernel=xxM". The value of xx is dependent
302 on the memory consumption of the kdump system. In general this is not
303 dependent on the memory size of the production system.
304
David Wilderdc851a02006-06-25 05:47:55 -0700305Load the Dump-capture Kernel
306============================
307
Vivek Goyal9c61a442007-01-10 23:15:35 -0800308After booting to the system kernel, dump-capture kernel needs to be
309loaded.
David Wilderdc851a02006-06-25 05:47:55 -0700310
Vivek Goyal9c61a442007-01-10 23:15:35 -0800311Based on the architecture and type of image (relocatable or not), one
312can choose to load the uncompressed vmlinux or compressed bzImage/vmlinuz
313of dump-capture kernel. Following is the summary.
314
Bernhard Walle8bc9d422007-10-16 23:31:21 -0700315For i386 and x86_64:
Vivek Goyal9c61a442007-01-10 23:15:35 -0800316 - Use vmlinux if kernel is not relocatable.
317 - Use bzImage/vmlinuz if kernel is relocatable.
Vivek Goyal9c61a442007-01-10 23:15:35 -0800318For ppc64:
319 - Use vmlinux
320For ia64:
Hormsee8bb9e2007-01-22 20:40:49 -0800321 - Use vmlinux or vmlinuz.gz
Michael Holzheu91302142011-12-27 11:27:25 +0100322For s390x:
323 - Use image or bzImage
Hormsee8bb9e2007-01-22 20:40:49 -0800324
Vivek Goyal9c61a442007-01-10 23:15:35 -0800325
326If you are using a uncompressed vmlinux image then use following command
327to load dump-capture kernel.
328
329 kexec -p <dump-capture-kernel-vmlinux-image> \
David Wilderdc851a02006-06-25 05:47:55 -0700330 --initrd=<initrd-for-dump-capture-kernel> --args-linux \
Vivek Goyal9c61a442007-01-10 23:15:35 -0800331 --append="root=<root-dev> <arch-specific-options>"
332
333If you are using a compressed bzImage/vmlinuz, then use following command
334to load dump-capture kernel.
335
336 kexec -p <dump-capture-kernel-bzImage> \
337 --initrd=<initrd-for-dump-capture-kernel> \
338 --append="root=<root-dev> <arch-specific-options>"
339
Hormsee8bb9e2007-01-22 20:40:49 -0800340Please note, that --args-linux does not need to be specified for ia64.
341It is planned to make this a no-op on that architecture, but for now
342it should be omitted
343
Vivek Goyal9c61a442007-01-10 23:15:35 -0800344Following are the arch specific command line options to be used while
345loading dump-capture kernel.
346
Hormsee8bb9e2007-01-22 20:40:49 -0800347For i386, x86_64 and ia64:
Bernhard Walleac984ab2007-10-16 23:31:23 -0700348 "1 irqpoll maxcpus=1 reset_devices"
Vivek Goyal9c61a442007-01-10 23:15:35 -0800349
350For ppc64:
Bernhard Walleac984ab2007-10-16 23:31:23 -0700351 "1 maxcpus=1 noirqdistrib reset_devices"
Vivek Goyal9c61a442007-01-10 23:15:35 -0800352
Michael Holzheu91302142011-12-27 11:27:25 +0100353For s390x:
354 "1 maxcpus=1 cgroup_disable=memory"
David Wilderdc851a02006-06-25 05:47:55 -0700355
356Notes on loading the dump-capture kernel:
357
David Wilderdc851a02006-06-25 05:47:55 -0700358* By default, the ELF headers are stored in ELF64 format to support
Bernhard Walle4fd45092007-10-16 23:31:22 -0700359 systems with more than 4GB memory. On i386, kexec automatically checks if
360 the physical RAM size exceeds the 4 GB limit and if not, uses ELF32.
361 So, on non-PAE systems, ELF32 is always used.
362
363 The --elf32-core-headers option can be used to force the generation of ELF32
364 headers. This is necessary because GDB currently cannot open vmcore files
365 with ELF64 headers on 32-bit systems.
David Wilderdc851a02006-06-25 05:47:55 -0700366
367* The "irqpoll" boot parameter reduces driver initialization failures
368 due to shared interrupts in the dump-capture kernel.
369
370* You must specify <root-dev> in the format corresponding to the root
371 device name in the output of mount command.
372
Horms473e66f2007-02-12 00:52:18 -0800373* Boot parameter "1" boots the dump-capture kernel into single-user
374 mode without networking. If you want networking, use "3".
David Wilderdc851a02006-06-25 05:47:55 -0700375
Vivek Goyal9c61a442007-01-10 23:15:35 -0800376* We generally don' have to bring up a SMP kernel just to capture the
377 dump. Hence generally it is useful either to build a UP dump-capture
378 kernel or specify maxcpus=1 option while loading dump-capture kernel.
David Wilderdc851a02006-06-25 05:47:55 -0700379
Michael Holzheu91302142011-12-27 11:27:25 +0100380* For s390x there are two kdump modes: If a ELF header is specified with
381 the elfcorehdr= kernel parameter, it is used by the kdump kernel as it
382 is done on all other architectures. If no elfcorehdr= kernel parameter is
383 specified, the s390x kdump kernel dynamically creates the header. The
384 second mode has the advantage that for CPU and memory hotplug, kdump has
385 not to be reloaded with kexec_load().
386
387* For s390x systems with many attached devices the "cio_ignore" kernel
388 parameter should be used for the kdump kernel in order to prevent allocation
389 of kernel memory for devices that are not relevant for kdump. The same
390 applies to systems that use SCSI/FCP devices. In that case the
391 "allow_lun_scan" zfcp module parameter should be set to zero before
392 setting FCP devices online.
393
David Wilderdc851a02006-06-25 05:47:55 -0700394Kernel Panic
395============
396
397After successfully loading the dump-capture kernel as previously
398described, the system will reboot into the dump-capture kernel if a
399system crash is triggered. Trigger points are located in panic(),
400die(), die_nmi() and in the sysrq handler (ALT-SysRq-c).
401
402The following conditions will execute a crash trigger point:
403
404If a hard lockup is detected and "NMI watchdog" is configured, the system
405will boot into the dump-capture kernel ( die_nmi() ).
406
407If die() is called, and it happens to be a thread with pid 0 or 1, or die()
408is called inside interrupt context or die() is called and panic_on_oops is set,
409the system will boot into the dump-capture kernel.
410
Pavel Machekf4e87572007-10-16 23:31:28 -0700411On powerpc systems when a soft-reset is generated, die() is called by all cpus
Simon Horman30430132007-02-20 13:58:07 -0800412and the system will boot into the dump-capture kernel.
David Wilderdc851a02006-06-25 05:47:55 -0700413
414For testing purposes, you can trigger a crash by using "ALT-SysRq-c",
Simon Horman30430132007-02-20 13:58:07 -0800415"echo c > /proc/sysrq-trigger" or write a module to force the panic.
David Wilderdc851a02006-06-25 05:47:55 -0700416
417Write Out the Dump File
418=======================
419
420After the dump-capture kernel is booted, write out the dump file with
421the following command:
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700422
423 cp /proc/vmcore <dump-file>
424
David Wilderdc851a02006-06-25 05:47:55 -0700425You can also access dumped memory as a /dev/oldmem device for a linear
426and raw view. To create the device, use the following command:
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700427
David Wilderdc851a02006-06-25 05:47:55 -0700428 mknod /dev/oldmem c 1 12
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700429
David Wilderdc851a02006-06-25 05:47:55 -0700430Use the dd command with suitable options for count, bs, and skip to
431access specific portions of the dump.
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700432
David Wilderdc851a02006-06-25 05:47:55 -0700433To see the entire memory, use the following command:
434
435 dd if=/dev/oldmem of=oldmem.001
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700436
Maneesh Sonia7e670d2006-01-09 20:51:53 -0800437
David Wilderdc851a02006-06-25 05:47:55 -0700438Analysis
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700439========
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700440
David Wilderdc851a02006-06-25 05:47:55 -0700441Before analyzing the dump image, you should reboot into a stable kernel.
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700442
David Wilderdc851a02006-06-25 05:47:55 -0700443You can do limited analysis using GDB on the dump file copied out of
444/proc/vmcore. Use the debug vmlinux built with -g and run the following
445command:
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700446
David Wilderdc851a02006-06-25 05:47:55 -0700447 gdb vmlinux <dump-file>
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700448
David Wilderdc851a02006-06-25 05:47:55 -0700449Stack trace for the task on processor 0, register display, and memory
450display work fine.
451
452Note: GDB cannot analyze core files generated in ELF64 format for x86.
453On systems with a maximum of 4GB of memory, you can generate
454ELF32-format headers using the --elf32-core-headers kernel option on the
455dump kernel.
456
457You can also use the Crash utility to analyze dump files in Kdump
458format. Crash is available on Dave Anderson's site at the following URL:
459
460 http://people.redhat.com/~anderson/
Maneesh Sonia7e670d2006-01-09 20:51:53 -0800461
462
David Wilderdc851a02006-06-25 05:47:55 -0700463To Do
464=====
465
Simon Horman30430132007-02-20 13:58:07 -08004661) Provide relocatable kernels for all architectures to help in maintaining
467 multiple kernels for crash_dump, and the same kernel as the system kernel
468 can be used to capture the dump.
Maneesh Sonia7e670d2006-01-09 20:51:53 -0800469
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700470
David Wilderdc851a02006-06-25 05:47:55 -0700471Contact
Vivek Goyalb089f4a2005-06-25 14:58:15 -0700472=======
David Wilderdc851a02006-06-25 05:47:55 -0700473
Simon Hormandb6857c2010-11-25 10:30:12 +0900474Vivek Goyal (vgoyal@redhat.com)
Vivek Goyald58831e2005-06-25 14:58:17 -0700475Maneesh Soni (maneesh@in.ibm.com)
David Wilderdc851a02006-06-25 05:47:55 -0700476