1 ============================================== 1 ================================================================
2 Documentation for Kdump - The kexec-based Cras 2 Documentation for Kdump - The kexec-based Crash Dumping Solution
3 ============================================== 3 ================================================================
4 4
5 This document includes overview, setup, instal 5 This document includes overview, setup, installation, and analysis
6 information. 6 information.
7 7
8 Overview 8 Overview
9 ======== 9 ========
10 10
11 Kdump uses kexec to quickly boot to a dump-cap 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 12 dump of the system kernel's memory needs to be taken (for example, when
13 the system panics). The system kernel's memory 13 the system panics). The system kernel's memory image is preserved across
14 the reboot and is accessible to the dump-captu 14 the reboot and is accessible to the dump-capture kernel.
15 15
16 You can use common commands, such as cp, scp o 16 You can use common commands, such as cp, scp or makedumpfile to copy
17 the memory image to a dump file on the local d 17 the memory image to a dump file on the local disk, or across the network
18 to a remote system. 18 to a remote system.
19 19
20 Kdump and kexec are currently supported on the 20 Kdump and kexec are currently supported on the x86, x86_64, ppc64,
21 s390x, arm and arm64 architectures. 21 s390x, arm and arm64 architectures.
22 22
23 When the system kernel boots, it reserves a sm 23 When the system kernel boots, it reserves a small section of memory for
24 the dump-capture kernel. This ensures that ong 24 the dump-capture kernel. This ensures that ongoing Direct Memory Access
25 (DMA) from the system kernel does not corrupt 25 (DMA) from the system kernel does not corrupt the dump-capture kernel.
26 The kexec -p command loads the dump-capture ke 26 The kexec -p command loads the dump-capture kernel into this reserved
27 memory. 27 memory.
28 28
29 On x86 machines, the first 640 KB of physical 29 On x86 machines, the first 640 KB of physical memory is needed for boot,
30 regardless of where the kernel loads. For simp 30 regardless of where the kernel loads. For simpler handling, the whole
31 low 1M is reserved to avoid any later kernel o 31 low 1M is reserved to avoid any later kernel or device driver writing
32 data into this area. Like this, the low 1M can 32 data into this area. Like this, the low 1M can be reused as system RAM
33 by kdump kernel without extra handling. 33 by kdump kernel without extra handling.
34 34
35 On PPC64 machines first 32KB of physical memor 35 On PPC64 machines first 32KB of physical memory is needed for booting
36 regardless of where the kernel is loaded and t 36 regardless of where the kernel is loaded and to support 64K page size
37 kexec backs up the first 64KB memory. 37 kexec backs up the first 64KB memory.
38 38
39 For s390x, when kdump is triggered, the crashk 39 For s390x, when kdump is triggered, the crashkernel region is exchanged
40 with the region [0, crashkernel region size] a 40 with the region [0, crashkernel region size] and then the kdump kernel
41 runs in [0, crashkernel region size]. Therefor 41 runs in [0, crashkernel region size]. Therefore no relocatable kernel is
42 needed for s390x. 42 needed for s390x.
43 43
44 All of the necessary information about the sys 44 All of the necessary information about the system kernel's core image is
45 encoded in the ELF format, and stored in a res 45 encoded in the ELF format, and stored in a reserved area of memory
46 before a crash. The physical address of the st 46 before a crash. The physical address of the start of the ELF header is
47 passed to the dump-capture kernel through the 47 passed to the dump-capture kernel through the elfcorehdr= boot
48 parameter. Optionally the size of the ELF head 48 parameter. Optionally the size of the ELF header can also be passed
49 when using the elfcorehdr=[size[KMG]@]offset[K 49 when using the elfcorehdr=[size[KMG]@]offset[KMG] syntax.
50 50
51 With the dump-capture kernel, you can access t 51 With the dump-capture kernel, you can access the memory image through
52 /proc/vmcore. This exports the dump as an ELF- 52 /proc/vmcore. This exports the dump as an ELF-format file that you can
53 write out using file copy commands such as cp 53 write out using file copy commands such as cp or scp. You can also use
54 makedumpfile utility to analyze and write out 54 makedumpfile utility to analyze and write out filtered contents with
55 options, e.g with '-d 31' it will only write o 55 options, e.g with '-d 31' it will only write out kernel data. Further,
56 you can use analysis tools such as the GNU Deb 56 you can use analysis tools such as the GNU Debugger (GDB) and the Crash
57 tool to debug the dump file. This method ensur 57 tool to debug the dump file. This method ensures that the dump pages are
58 correctly ordered. 58 correctly ordered.
59 59
60 Setup and Installation 60 Setup and Installation
61 ====================== 61 ======================
62 62
63 Install kexec-tools 63 Install kexec-tools
64 ------------------- 64 -------------------
65 65
66 1) Login as the root user. 66 1) Login as the root user.
67 67
68 2) Download the kexec-tools user-space package 68 2) Download the kexec-tools user-space package from the following URL:
69 69
70 http://kernel.org/pub/linux/utils/kernel/kexec 70 http://kernel.org/pub/linux/utils/kernel/kexec/kexec-tools.tar.gz
71 71
72 This is a symlink to the latest version. 72 This is a symlink to the latest version.
73 73
74 The latest kexec-tools git tree is available a 74 The latest kexec-tools git tree is available at:
75 75
76 - git://git.kernel.org/pub/scm/utils/kernel/ke 76 - git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
77 - http://www.kernel.org/pub/scm/utils/kernel/k 77 - http://www.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
78 78
79 There is also a gitweb interface available at 79 There is also a gitweb interface available at
80 http://www.kernel.org/git/?p=utils/kernel/kexe 80 http://www.kernel.org/git/?p=utils/kernel/kexec/kexec-tools.git
81 81
82 More information about kexec-tools can be foun 82 More information about kexec-tools can be found at
83 http://horms.net/projects/kexec/ 83 http://horms.net/projects/kexec/
84 84
85 3) Unpack the tarball with the tar command, as 85 3) Unpack the tarball with the tar command, as follows::
86 86
87 tar xvpzf kexec-tools.tar.gz 87 tar xvpzf kexec-tools.tar.gz
88 88
89 4) Change to the kexec-tools directory, as fol 89 4) Change to the kexec-tools directory, as follows::
90 90
91 cd kexec-tools-VERSION 91 cd kexec-tools-VERSION
92 92
93 5) Configure the package, as follows:: 93 5) Configure the package, as follows::
94 94
95 ./configure 95 ./configure
96 96
97 6) Compile the package, as follows:: 97 6) Compile the package, as follows::
98 98
99 make 99 make
100 100
101 7) Install the package, as follows:: 101 7) Install the package, as follows::
102 102
103 make install 103 make install
104 104
105 105
106 Build the system and dump-capture kernels 106 Build the system and dump-capture kernels
107 ----------------------------------------- 107 -----------------------------------------
108 There are two possible methods of using Kdump. 108 There are two possible methods of using Kdump.
109 109
110 1) Build a separate custom dump-capture kernel 110 1) Build a separate custom dump-capture kernel for capturing the
111 kernel core dump. 111 kernel core dump.
112 112
113 2) Or use the system kernel binary itself as d 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 ke 114 no need to build a separate dump-capture kernel. This is possible
115 only with the architectures which support a 115 only with the architectures which support a relocatable kernel. As
116 of today, i386, x86_64, ppc64, arm and arm6 116 of today, i386, x86_64, ppc64, arm and arm64 architectures support
117 relocatable kernel. 117 relocatable kernel.
118 118
119 Building a relocatable kernel is advantageous 119 Building a relocatable kernel is advantageous from the point of view that
120 one does not have to build a second kernel for 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 cus 121 at the same time one might want to build a custom dump capture kernel
122 suitable to his needs. 122 suitable to his needs.
123 123
124 Following are the configuration setting requir 124 Following are the configuration setting required for system and
125 dump-capture kernels for enabling kdump suppor 125 dump-capture kernels for enabling kdump support.
126 126
127 System kernel config options 127 System kernel config options
128 ---------------------------- 128 ----------------------------
129 129
130 1) Enable "kexec system call" or "kexec file b 130 1) Enable "kexec system call" or "kexec file based system call" in
131 "Processor type and features.":: 131 "Processor type and features."::
132 132
133 CONFIG_KEXEC=y or CONFIG_KEXEC_FILE=y 133 CONFIG_KEXEC=y or CONFIG_KEXEC_FILE=y
134 134
135 And both of them will select KEXEC_CORE:: 135 And both of them will select KEXEC_CORE::
136 136
137 CONFIG_KEXEC_CORE=y 137 CONFIG_KEXEC_CORE=y
138 138
>> 139 Subsequently, CRASH_CORE is selected by KEXEC_CORE::
>> 140
>> 141 CONFIG_CRASH_CORE=y
>> 142
139 2) Enable "sysfs file system support" in "File 143 2) Enable "sysfs file system support" in "Filesystem" -> "Pseudo
140 filesystems." This is usually enabled by de 144 filesystems." This is usually enabled by default::
141 145
142 CONFIG_SYSFS=y 146 CONFIG_SYSFS=y
143 147
144 Note that "sysfs file system support" might 148 Note that "sysfs file system support" might not appear in the "Pseudo
145 filesystems" menu if "Configure standard ke 149 filesystems" menu if "Configure standard kernel features (expert users)"
146 is not enabled in "General Setup." In this 150 is not enabled in "General Setup." In this case, check the .config file
147 itself to ensure that sysfs is turned on, a 151 itself to ensure that sysfs is turned on, as follows::
148 152
149 grep 'CONFIG_SYSFS' .config 153 grep 'CONFIG_SYSFS' .config
150 154
151 3) Enable "Compile the kernel with debug info" 155 3) Enable "Compile the kernel with debug info" in "Kernel hacking."::
152 156
153 CONFIG_DEBUG_INFO=Y 157 CONFIG_DEBUG_INFO=Y
154 158
155 This causes the kernel to be built with deb 159 This causes the kernel to be built with debug symbols. The dump
156 analysis tools require a vmlinux with debug 160 analysis tools require a vmlinux with debug symbols in order to read
157 and analyze a dump file. 161 and analyze a dump file.
158 162
159 Dump-capture kernel config options (Arch Indep 163 Dump-capture kernel config options (Arch Independent)
160 ---------------------------------------------- 164 -----------------------------------------------------
161 165
162 1) Enable "kernel crash dumps" support under " 166 1) Enable "kernel crash dumps" support under "Processor type and
163 features":: 167 features"::
164 168
165 CONFIG_CRASH_DUMP=y 169 CONFIG_CRASH_DUMP=y
166 <<
167 And this will select VMCORE_INFO and CRASH_ <<
168 CONFIG_VMCORE_INFO=y <<
169 CONFIG_CRASH_RESERVE=y <<
170 170
171 2) Enable "/proc/vmcore support" under "Filesy 171 2) Enable "/proc/vmcore support" under "Filesystems" -> "Pseudo filesystems"::
172 172
173 CONFIG_PROC_VMCORE=y 173 CONFIG_PROC_VMCORE=y
174 174
175 (CONFIG_PROC_VMCORE is set by default when 175 (CONFIG_PROC_VMCORE is set by default when CONFIG_CRASH_DUMP is selected.)
176 176
177 Dump-capture kernel config options (Arch Depen 177 Dump-capture kernel config options (Arch Dependent, i386 and x86_64)
178 ---------------------------------------------- 178 --------------------------------------------------------------------
179 179
180 1) On i386, enable high memory support under " 180 1) On i386, enable high memory support under "Processor type and
181 features":: 181 features"::
182 182
183 CONFIG_HIGHMEM64G=y 183 CONFIG_HIGHMEM64G=y
184 184
185 or:: 185 or::
186 186
187 CONFIG_HIGHMEM4G 187 CONFIG_HIGHMEM4G
188 188
189 2) With CONFIG_SMP=y, usually nr_cpus=1 need s 189 2) With CONFIG_SMP=y, usually nr_cpus=1 need specified on the kernel
190 command line when loading the dump-capture 190 command line when loading the dump-capture kernel because one
191 CPU is enough for kdump kernel to dump vmco 191 CPU is enough for kdump kernel to dump vmcore on most of systems.
192 192
193 However, you can also specify nr_cpus=X to 193 However, you can also specify nr_cpus=X to enable multiple processors
194 in kdump kernel. 194 in kdump kernel.
195 195
196 With CONFIG_SMP=n, the above things are not 196 With CONFIG_SMP=n, the above things are not related.
197 197
198 3) A relocatable kernel is suggested to be bui 198 3) A relocatable kernel is suggested to be built by default. If not yet,
199 enable "Build a relocatable kernel" support 199 enable "Build a relocatable kernel" support under "Processor type and
200 features":: 200 features"::
201 201
202 CONFIG_RELOCATABLE=y 202 CONFIG_RELOCATABLE=y
203 203
204 4) Use a suitable value for "Physical address 204 4) Use a suitable value for "Physical address where the kernel is
205 loaded" (under "Processor type and features 205 loaded" (under "Processor type and features"). This only appears when
206 "kernel crash dumps" is enabled. A suitable 206 "kernel crash dumps" is enabled. A suitable value depends upon
207 whether kernel is relocatable or not. 207 whether kernel is relocatable or not.
208 208
209 If you are using a relocatable kernel use C 209 If you are using a relocatable kernel use CONFIG_PHYSICAL_START=0x100000
210 This will compile the kernel for physical a 210 This will compile the kernel for physical address 1MB, but given the fact
211 kernel is relocatable, it can be run from a 211 kernel is relocatable, it can be run from any physical address hence
212 kexec boot loader will load it in memory re 212 kexec boot loader will load it in memory region reserved for dump-capture
213 kernel. 213 kernel.
214 214
215 Otherwise it should be the start of memory 215 Otherwise it should be the start of memory region reserved for
216 second kernel using boot parameter "crashke 216 second kernel using boot parameter "crashkernel=Y@X". Here X is
217 start of memory region reserved for dump-ca 217 start of memory region reserved for dump-capture kernel.
218 Generally X is 16MB (0x1000000). So you can 218 Generally X is 16MB (0x1000000). So you can set
219 CONFIG_PHYSICAL_START=0x1000000 219 CONFIG_PHYSICAL_START=0x1000000
220 220
221 5) Make and install the kernel and its modules 221 5) Make and install the kernel and its modules. DO NOT add this kernel
222 to the boot loader configuration files. 222 to the boot loader configuration files.
223 223
224 Dump-capture kernel config options (Arch Depen 224 Dump-capture kernel config options (Arch Dependent, ppc64)
225 ---------------------------------------------- 225 ----------------------------------------------------------
226 226
227 1) Enable "Build a kdump crash kernel" support 227 1) Enable "Build a kdump crash kernel" support under "Kernel" options::
228 228
229 CONFIG_CRASH_DUMP=y 229 CONFIG_CRASH_DUMP=y
230 230
231 2) Enable "Build a relocatable kernel" suppo 231 2) Enable "Build a relocatable kernel" support::
232 232
233 CONFIG_RELOCATABLE=y 233 CONFIG_RELOCATABLE=y
234 234
235 Make and install the kernel and its modules 235 Make and install the kernel and its modules.
236 236
237 Dump-capture kernel config options (Arch Depen 237 Dump-capture kernel config options (Arch Dependent, arm)
238 ---------------------------------------------- 238 ----------------------------------------------------------
239 239
240 - To use a relocatable kernel, 240 - To use a relocatable kernel,
241 Enable "AUTO_ZRELADDR" support under "Boot 241 Enable "AUTO_ZRELADDR" support under "Boot" options::
242 242
243 AUTO_ZRELADDR=y 243 AUTO_ZRELADDR=y
244 244
245 Dump-capture kernel config options (Arch Depen 245 Dump-capture kernel config options (Arch Dependent, arm64)
246 ---------------------------------------------- 246 ----------------------------------------------------------
247 247
248 - Please note that kvm of the dump-capture ker 248 - Please note that kvm of the dump-capture kernel will not be enabled
249 on non-VHE systems even if it is configured. 249 on non-VHE systems even if it is configured. This is because the CPU
250 will not be reset to EL2 on panic. 250 will not be reset to EL2 on panic.
251 251
252 crashkernel syntax 252 crashkernel syntax
253 =========================== 253 ===========================
254 1) crashkernel=size@offset 254 1) crashkernel=size@offset
255 255
256 Here 'size' specifies how much memory to re 256 Here 'size' specifies how much memory to reserve for the dump-capture kernel
257 and 'offset' specifies the beginning of thi 257 and 'offset' specifies the beginning of this reserved memory. For example,
258 "crashkernel=64M@16M" tells the system kern 258 "crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory
259 starting at physical address 0x01000000 (16 259 starting at physical address 0x01000000 (16MB) for the dump-capture kernel.
260 260
261 The crashkernel region can be automatically 261 The crashkernel region can be automatically placed by the system
262 kernel at run time. This is done by specify 262 kernel at run time. This is done by specifying the base address as 0,
263 or omitting it all together:: 263 or omitting it all together::
264 264
265 crashkernel=256M@0 265 crashkernel=256M@0
266 266
267 or:: 267 or::
268 268
269 crashkernel=256M 269 crashkernel=256M
270 270
271 If the start address is specified, note tha 271 If the start address is specified, note that the start address of the
272 kernel will be aligned to a value (which is 272 kernel will be aligned to a value (which is Arch dependent), so if the
273 start address is not then any space below t 273 start address is not then any space below the alignment point will be
274 wasted. 274 wasted.
275 275
276 2) range1:size1[,range2:size2,...][@offset] 276 2) range1:size1[,range2:size2,...][@offset]
277 277
278 While the "crashkernel=size[@offset]" synta 278 While the "crashkernel=size[@offset]" syntax is sufficient for most
279 configurations, sometimes it's handy to hav 279 configurations, sometimes it's handy to have the reserved memory dependent
280 on the value of System RAM -- that's mostly 280 on the value of System RAM -- that's mostly for distributors that pre-setup
281 the kernel command line to avoid a unbootab 281 the kernel command line to avoid a unbootable system after some memory has
282 been removed from the machine. 282 been removed from the machine.
283 283
284 The syntax is:: 284 The syntax is::
285 285
286 crashkernel=<range1>:<size1>[,<range2>: 286 crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
287 range=start-[end] 287 range=start-[end]
288 288
289 For example:: 289 For example::
290 290
291 crashkernel=512M-2G:64M,2G-:128M 291 crashkernel=512M-2G:64M,2G-:128M
292 292
293 This would mean: 293 This would mean:
294 294
295 1) if the RAM is smaller than 512M, the 295 1) if the RAM is smaller than 512M, then don't reserve anything
296 (this is the "rescue" case) 296 (this is the "rescue" case)
297 2) if the RAM size is between 512M and 297 2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
298 3) if the RAM size is larger than 2G, t 298 3) if the RAM size is larger than 2G, then reserve 128M
299 299
300 3) crashkernel=size,high and crashkernel=size, 300 3) crashkernel=size,high and crashkernel=size,low
301 301
302 If memory above 4G is preferred, crashkerne 302 If memory above 4G is preferred, crashkernel=size,high can be used to
303 fulfill that. With it, physical memory is a 303 fulfill that. With it, physical memory is allowed to be allocated from top,
304 so could be above 4G if system has more tha 304 so could be above 4G if system has more than 4G RAM installed. Otherwise,
305 memory region will be allocated below 4G if 305 memory region will be allocated below 4G if available.
306 306
307 When crashkernel=X,high is passed, kernel c 307 When crashkernel=X,high is passed, kernel could allocate physical memory
308 region above 4G, low memory under 4G is nee 308 region above 4G, low memory under 4G is needed in this case. There are
309 three ways to get low memory: 309 three ways to get low memory:
310 310
311 1) Kernel will allocate at least 256M me 311 1) Kernel will allocate at least 256M memory below 4G automatically
312 if crashkernel=Y,low is not specified 312 if crashkernel=Y,low is not specified.
313 2) Let user specify low memory size inst 313 2) Let user specify low memory size instead.
314 3) Specified value 0 will disable low me 314 3) Specified value 0 will disable low memory allocation::
315 315
316 crashkernel=0,low 316 crashkernel=0,low
317 317
318 Boot into System Kernel 318 Boot into System Kernel
319 ----------------------- 319 -----------------------
320 1) Update the boot loader (such as grub, yaboo 320 1) Update the boot loader (such as grub, yaboot, or lilo) configuration
321 files as necessary. 321 files as necessary.
322 322
323 2) Boot the system kernel with the boot parame 323 2) Boot the system kernel with the boot parameter "crashkernel=Y@X".
324 324
325 On x86 and x86_64, use "crashkernel=Y[@X]". 325 On x86 and x86_64, use "crashkernel=Y[@X]". Most of the time, the
326 start address 'X' is not necessary, kernel 326 start address 'X' is not necessary, kernel will search a suitable
327 area. Unless an explicit start address is e 327 area. Unless an explicit start address is expected.
328 328
329 On ppc64, use "crashkernel=128M@32M". 329 On ppc64, use "crashkernel=128M@32M".
330 330
331 On s390x, typically use "crashkernel=xxM". 331 On s390x, typically use "crashkernel=xxM". The value of xx is dependent
332 on the memory consumption of the kdump syst 332 on the memory consumption of the kdump system. In general this is not
333 dependent on the memory size of the product 333 dependent on the memory size of the production system.
334 334
335 On arm, the use of "crashkernel=Y@X" is no 335 On arm, the use of "crashkernel=Y@X" is no longer necessary; the
336 kernel will automatically locate the crash 336 kernel will automatically locate the crash kernel image within the
337 first 512MB of RAM if X is not given. 337 first 512MB of RAM if X is not given.
338 338
339 On arm64, use "crashkernel=Y[@X]". Note th 339 On arm64, use "crashkernel=Y[@X]". Note that the start address of
340 the kernel, X if explicitly specified, must 340 the kernel, X if explicitly specified, must be aligned to 2MiB (0x200000).
341 341
342 Load the Dump-capture Kernel 342 Load the Dump-capture Kernel
343 ============================ 343 ============================
344 344
345 After booting to the system kernel, dump-captu 345 After booting to the system kernel, dump-capture kernel needs to be
346 loaded. 346 loaded.
347 347
348 Based on the architecture and type of image (r 348 Based on the architecture and type of image (relocatable or not), one
349 can choose to load the uncompressed vmlinux or 349 can choose to load the uncompressed vmlinux or compressed bzImage/vmlinuz
350 of dump-capture kernel. Following is the summa 350 of dump-capture kernel. Following is the summary.
351 351
352 For i386 and x86_64: 352 For i386 and x86_64:
353 353
354 - Use bzImage/vmlinuz if kernel is rel 354 - Use bzImage/vmlinuz if kernel is relocatable.
355 - Use vmlinux if kernel is not relocat 355 - Use vmlinux if kernel is not relocatable.
356 356
357 For ppc64: 357 For ppc64:
358 358
359 - Use vmlinux 359 - Use vmlinux
360 360
361 For s390x: 361 For s390x:
362 362
363 - Use image or bzImage 363 - Use image or bzImage
364 364
365 For arm: 365 For arm:
366 366
367 - Use zImage 367 - Use zImage
368 368
369 For arm64: 369 For arm64:
370 370
371 - Use vmlinux or Image 371 - Use vmlinux or Image
372 372
373 If you are using an uncompressed vmlinux image 373 If you are using an uncompressed vmlinux image then use following command
374 to load dump-capture kernel:: 374 to load dump-capture kernel::
375 375
376 kexec -p <dump-capture-kernel-vmlinux-image 376 kexec -p <dump-capture-kernel-vmlinux-image> \
377 --initrd=<initrd-for-dump-capture-kernel> - 377 --initrd=<initrd-for-dump-capture-kernel> --args-linux \
378 --append="root=<root-dev> <arch-specific-op 378 --append="root=<root-dev> <arch-specific-options>"
379 379
380 If you are using a compressed bzImage/vmlinuz, 380 If you are using a compressed bzImage/vmlinuz, then use following command
381 to load dump-capture kernel:: 381 to load dump-capture kernel::
382 382
383 kexec -p <dump-capture-kernel-bzImage> \ 383 kexec -p <dump-capture-kernel-bzImage> \
384 --initrd=<initrd-for-dump-capture-kernel> \ 384 --initrd=<initrd-for-dump-capture-kernel> \
385 --append="root=<root-dev> <arch-specific-op 385 --append="root=<root-dev> <arch-specific-options>"
386 386
387 If you are using a compressed zImage, then use 387 If you are using a compressed zImage, then use following command
388 to load dump-capture kernel:: 388 to load dump-capture kernel::
389 389
390 kexec --type zImage -p <dump-capture-kernel 390 kexec --type zImage -p <dump-capture-kernel-bzImage> \
391 --initrd=<initrd-for-dump-capture-kernel> \ 391 --initrd=<initrd-for-dump-capture-kernel> \
392 --dtb=<dtb-for-dump-capture-kernel> \ 392 --dtb=<dtb-for-dump-capture-kernel> \
393 --append="root=<root-dev> <arch-specific-op 393 --append="root=<root-dev> <arch-specific-options>"
394 394
395 If you are using an uncompressed Image, then u 395 If you are using an uncompressed Image, then use following command
396 to load dump-capture kernel:: 396 to load dump-capture kernel::
397 397
398 kexec -p <dump-capture-kernel-Image> \ 398 kexec -p <dump-capture-kernel-Image> \
399 --initrd=<initrd-for-dump-capture-kernel> \ 399 --initrd=<initrd-for-dump-capture-kernel> \
400 --append="root=<root-dev> <arch-specific-op 400 --append="root=<root-dev> <arch-specific-options>"
401 401
402 Following are the arch specific command line o 402 Following are the arch specific command line options to be used while
403 loading dump-capture kernel. 403 loading dump-capture kernel.
404 404
405 For i386 and x86_64: 405 For i386 and x86_64:
406 406
407 "1 irqpoll nr_cpus=1 reset_devices" 407 "1 irqpoll nr_cpus=1 reset_devices"
408 408
409 For ppc64: 409 For ppc64:
410 410
411 "1 maxcpus=1 noirqdistrib reset_device 411 "1 maxcpus=1 noirqdistrib reset_devices"
412 412
413 For s390x: 413 For s390x:
414 414
415 "1 nr_cpus=1 cgroup_disable=memory" 415 "1 nr_cpus=1 cgroup_disable=memory"
416 416
417 For arm: 417 For arm:
418 418
419 "1 maxcpus=1 reset_devices" 419 "1 maxcpus=1 reset_devices"
420 420
421 For arm64: 421 For arm64:
422 422
423 "1 nr_cpus=1 reset_devices" 423 "1 nr_cpus=1 reset_devices"
424 424
425 Notes on loading the dump-capture kernel: 425 Notes on loading the dump-capture kernel:
426 426
427 * By default, the ELF headers are stored in EL 427 * By default, the ELF headers are stored in ELF64 format to support
428 systems with more than 4GB memory. On i386, 428 systems with more than 4GB memory. On i386, kexec automatically checks if
429 the physical RAM size exceeds the 4 GB limit 429 the physical RAM size exceeds the 4 GB limit and if not, uses ELF32.
430 So, on non-PAE systems, ELF32 is always used 430 So, on non-PAE systems, ELF32 is always used.
431 431
432 The --elf32-core-headers option can be used 432 The --elf32-core-headers option can be used to force the generation of ELF32
433 headers. This is necessary because GDB curre 433 headers. This is necessary because GDB currently cannot open vmcore files
434 with ELF64 headers on 32-bit systems. 434 with ELF64 headers on 32-bit systems.
435 435
436 * The "irqpoll" boot parameter reduces driver 436 * The "irqpoll" boot parameter reduces driver initialization failures
437 due to shared interrupts in the dump-capture 437 due to shared interrupts in the dump-capture kernel.
438 438
439 * You must specify <root-dev> in the format co 439 * You must specify <root-dev> in the format corresponding to the root
440 device name in the output of mount command. 440 device name in the output of mount command.
441 441
442 * Boot parameter "1" boots the dump-capture ke 442 * Boot parameter "1" boots the dump-capture kernel into single-user
443 mode without networking. If you want network 443 mode without networking. If you want networking, use "3".
444 444
445 * We generally don't have to bring up a SMP ke 445 * We generally don't have to bring up a SMP kernel just to capture the
446 dump. Hence generally it is useful either to 446 dump. Hence generally it is useful either to build a UP dump-capture
447 kernel or specify maxcpus=1 option while loa 447 kernel or specify maxcpus=1 option while loading dump-capture kernel.
448 Note, though maxcpus always works, you had b 448 Note, though maxcpus always works, you had better replace it with
449 nr_cpus to save memory if supported by the c 449 nr_cpus to save memory if supported by the current ARCH, such as x86.
450 450
451 * You should enable multi-cpu support in dump- 451 * You should enable multi-cpu support in dump-capture kernel if you intend
452 to use multi-thread programs with it, such a 452 to use multi-thread programs with it, such as parallel dump feature of
453 makedumpfile. Otherwise, the multi-thread pr 453 makedumpfile. Otherwise, the multi-thread program may have a great
454 performance degradation. To enable multi-cpu 454 performance degradation. To enable multi-cpu support, you should bring up an
455 SMP dump-capture kernel and specify maxcpus/ 455 SMP dump-capture kernel and specify maxcpus/nr_cpus options while loading it.
456 456
457 * For s390x there are two kdump modes: If a EL 457 * For s390x there are two kdump modes: If a ELF header is specified with
458 the elfcorehdr= kernel parameter, it is used 458 the elfcorehdr= kernel parameter, it is used by the kdump kernel as it
459 is done on all other architectures. If no el 459 is done on all other architectures. If no elfcorehdr= kernel parameter is
460 specified, the s390x kdump kernel dynamicall 460 specified, the s390x kdump kernel dynamically creates the header. The
461 second mode has the advantage that for CPU a 461 second mode has the advantage that for CPU and memory hotplug, kdump has
462 not to be reloaded with kexec_load(). 462 not to be reloaded with kexec_load().
463 463
464 * For s390x systems with many attached devices 464 * For s390x systems with many attached devices the "cio_ignore" kernel
465 parameter should be used for the kdump kerne 465 parameter should be used for the kdump kernel in order to prevent allocation
466 of kernel memory for devices that are not re 466 of kernel memory for devices that are not relevant for kdump. The same
467 applies to systems that use SCSI/FCP devices 467 applies to systems that use SCSI/FCP devices. In that case the
468 "allow_lun_scan" zfcp module parameter shoul 468 "allow_lun_scan" zfcp module parameter should be set to zero before
469 setting FCP devices online. 469 setting FCP devices online.
470 470
471 Kernel Panic 471 Kernel Panic
472 ============ 472 ============
473 473
474 After successfully loading the dump-capture ke 474 After successfully loading the dump-capture kernel as previously
475 described, the system will reboot into the dum 475 described, the system will reboot into the dump-capture kernel if a
476 system crash is triggered. Trigger points are 476 system crash is triggered. Trigger points are located in panic(),
477 die(), die_nmi() and in the sysrq handler (ALT 477 die(), die_nmi() and in the sysrq handler (ALT-SysRq-c).
478 478
479 The following conditions will execute a crash 479 The following conditions will execute a crash trigger point:
480 480
481 If a hard lockup is detected and "NMI watchdog 481 If a hard lockup is detected and "NMI watchdog" is configured, the system
482 will boot into the dump-capture kernel ( die_n 482 will boot into the dump-capture kernel ( die_nmi() ).
483 483
484 If die() is called, and it happens to be a thr 484 If die() is called, and it happens to be a thread with pid 0 or 1, or die()
485 is called inside interrupt context or die() is 485 is called inside interrupt context or die() is called and panic_on_oops is set,
486 the system will boot into the dump-capture ker 486 the system will boot into the dump-capture kernel.
487 487
488 On powerpc systems when a soft-reset is genera 488 On powerpc systems when a soft-reset is generated, die() is called by all cpus
489 and the system will boot into the dump-capture 489 and the system will boot into the dump-capture kernel.
490 490
491 For testing purposes, you can trigger a crash 491 For testing purposes, you can trigger a crash by using "ALT-SysRq-c",
492 "echo c > /proc/sysrq-trigger" or write a modu 492 "echo c > /proc/sysrq-trigger" or write a module to force the panic.
493 493
494 Write Out the Dump File 494 Write Out the Dump File
495 ======================= 495 =======================
496 496
497 After the dump-capture kernel is booted, write 497 After the dump-capture kernel is booted, write out the dump file with
498 the following command:: 498 the following command::
499 499
500 cp /proc/vmcore <dump-file> 500 cp /proc/vmcore <dump-file>
501 501
502 or use scp to write out the dump file between 502 or use scp to write out the dump file between hosts on a network, e.g::
503 503
504 scp /proc/vmcore remote_username@remote_ip: 504 scp /proc/vmcore remote_username@remote_ip:<dump-file>
505 505
506 You can also use makedumpfile utility to write 506 You can also use makedumpfile utility to write out the dump file
507 with specified options to filter out unwanted 507 with specified options to filter out unwanted contents, e.g::
508 508
509 makedumpfile -l --message-level 1 -d 31 /pr 509 makedumpfile -l --message-level 1 -d 31 /proc/vmcore <dump-file>
510 510
511 Analysis 511 Analysis
512 ======== 512 ========
513 513
514 Before analyzing the dump image, you should re 514 Before analyzing the dump image, you should reboot into a stable kernel.
515 515
516 You can do limited analysis using GDB on the d 516 You can do limited analysis using GDB on the dump file copied out of
517 /proc/vmcore. Use the debug vmlinux built with 517 /proc/vmcore. Use the debug vmlinux built with -g and run the following
518 command:: 518 command::
519 519
520 gdb vmlinux <dump-file> 520 gdb vmlinux <dump-file>
521 521
522 Stack trace for the task on processor 0, regis 522 Stack trace for the task on processor 0, register display, and memory
523 display work fine. 523 display work fine.
524 524
525 Note: GDB cannot analyze core files generated 525 Note: GDB cannot analyze core files generated in ELF64 format for x86.
526 On systems with a maximum of 4GB of memory, yo 526 On systems with a maximum of 4GB of memory, you can generate
527 ELF32-format headers using the --elf32-core-he 527 ELF32-format headers using the --elf32-core-headers kernel option on the
528 dump kernel. 528 dump kernel.
529 529
530 You can also use the Crash utility to analyze 530 You can also use the Crash utility to analyze dump files in Kdump
531 format. Crash is available at the following UR 531 format. Crash is available at the following URL:
532 532
533 https://github.com/crash-utility/crash 533 https://github.com/crash-utility/crash
534 534
535 Crash document can be found at: 535 Crash document can be found at:
536 https://crash-utility.github.io/ 536 https://crash-utility.github.io/
537 537
538 Trigger Kdump on WARN() 538 Trigger Kdump on WARN()
539 ======================= 539 =======================
540 540
541 The kernel parameter, panic_on_warn, calls pan 541 The kernel parameter, panic_on_warn, calls panic() in all WARN() paths. This
542 will cause a kdump to occur at the panic() cal 542 will cause a kdump to occur at the panic() call. In cases where a user wants
543 to specify this during runtime, /proc/sys/kern 543 to specify this during runtime, /proc/sys/kernel/panic_on_warn can be set to 1
544 to achieve the same behaviour. 544 to achieve the same behaviour.
545 545
546 Trigger Kdump on add_taint() 546 Trigger Kdump on add_taint()
547 ============================ 547 ============================
548 548
549 The kernel parameter panic_on_taint facilitate 549 The kernel parameter panic_on_taint facilitates a conditional call to panic()
550 from within add_taint() whenever the value set 550 from within add_taint() whenever the value set in this bitmask matches with the
551 bit flag being set by add_taint(). 551 bit flag being set by add_taint().
552 This will cause a kdump to occur at the add_ta 552 This will cause a kdump to occur at the add_taint()->panic() call.
553 553
554 Contact 554 Contact
555 ======= 555 =======
556 556
557 - kexec@lists.infradead.org 557 - kexec@lists.infradead.org
558 558
559 GDB macros 559 GDB macros
560 ========== 560 ==========
561 561
562 .. include:: gdbmacros.txt 562 .. include:: gdbmacros.txt
563 :literal: 563 :literal:
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