Documentation feedback request.
A message that is not in the archive (sent off-list or not yet received): [email protected]
Hi David,
Nice work. Few comments below ...
Quoted 19 lines · David Wilder
Attached is a updated
Documentation/kdump/kdump.txt. Please provide comments. I will incorporate your feedback and send up to Linus.plain text document attachment (kdump-final-20060425.txt)
================================================================
Documentation for Kdump - The kexec-based Crash Dumping Solution
================================================================This document includes overview, setup and installation, and analysis information.
Overview
========Kdump uses kexec to quickly boot to a dump-capture kernel whenever a dump of the system kernel's memory needs to be taken (for example, when the system panics). The system kernel's memory image is preserved across the reboot and is accessible to the dump-capture kernel.
Quoted 6 lines
You can use common Linux commands, such as cp and scp, to copy the memory image to a dump file on the local disk, or across the network to a remote system.
Kdump and kexec are currently supported on the x86,
x86_64, and ppc64 architectures.
s/ppc64/64-bit powerpc/ ?
Quoted 5 lines
When the system kernel boots, it reserves a small section of memory for the dump-capture kernel. This ensures that ongoing Direct Memory Access (DMA) from the system kernel does not corrupt the dump-capture kernel. The kexec -p command loads the dump-capture kernel into this reserved memory.
Well hopefully ;)
Quoted 89 lines
On x86 machines, the first 640 KB of physical memory is needed to boot, regardless of where the kernel loads. Therefore, kexec backs up this region just before rebooting into the dump-capture kernel.
All of the necessary information about the system kernel's core image is encoded in the ELF format, and stored in a reserved area of memory before a crash. The physical address of the start of the ELF header is passed to the dump-capture kernel through the elfcorehdr= boot parameter.
With the dump-capture kernel, you can access the memory image, or "old memory," in two ways:
- Through a
/dev/oldmemdevice interface. A capture utility can read the device file and write out the memory in raw format. This is a raw dump of memory. Analysis and capture tools must be intelligent enough to determine where to look for the right information.- Through
/proc/vmcore. This exports the dump as an ELF-format file that you can write out using file copy commands such as cp or scp. Further, you can use analysis tools such as the GNU Debugger (GDB) and the Crash tool to debug the dump file. This method ensures that the dump pages are correctly ordered.Setup and Installation
======================Install kexec-tools and the Kdump patch
---------------------------------------1) Login as the root user.
2) Download the kexec-tools user-space package from the following URL:
http://www.xmission.com/~ebiederm/files/kexec/kexec-tools-1.101.tar.gz3) Unpack the tarball with the tar command, as follows:
tar xvpzf kexec-tools-1.101.tar.gz4) Download the latest consolidated Kdump patch from the following URL:
http://lse.sourceforge.net/kdump/
(This location is being used until all the user-space Kdump patches are integrated with the kexec-tools package.)
5) Change to the kexec-tools-1.101 directory, as follows:
cd kexec-tools-1.1016) Apply the consolidated patch to the kexec-tools-1.101 source tree with the patch command, as follows. (Modify the path to the downloaded patch as necessary.)
patch -p1 < /path-to-kdump-patch/kexec-tools-1.101-kdump.patch7) Configure the package, as follows:
./configure
8) Compile the package, as follows:
make
9) Install the package, as follows:
make install
Download and build the system and dump-capture kernels
------------------------------------------------------Download the mainline (vanilla) kernel source code (2.6.13-rc1 or newer) from http://www.kernel.org. Two kernels must be built: a system kernel and a dump-capture kernel. Use the following steps to configure these kernels with the necessary kexec and Kdump features:
System kernel
-------------1) Enable "kexec system call" in "Processor type and features."
CONFIG_KEXEC=y2) Enable "sysfs file system support" in "Filesystem" -> "Pseudo filesystems." This is usually enabled by default.
Quoted 8 lines
CONFIG_SYSFS=yNote that "sysfs file system support" might not appear in the "Pseudo filesystems" menu if "Configure standard kernel features (for small systems)" is not enabled in "General Setup." In this case, check the .config file itself to ensure that sysfs is turned on, as follows:
grep '
CONFIG_SYSFS' .config
Is there a particular requirement for sysfs?
Quoted 8 lines
3) Enable "Compile the kernel with debug info" in "Kernel hacking."
CONFIG_DEBUG_INFO=YThis causes the kernel to be built with debug symbols. The dump analysis tools require a vmlinux with debug symbols in order to read and analyze a dump file.
Quoted 8 lines
4) Make and install the kernel and its modules. Update the boot loader (such as grub, yaboot, or lilo) configuration files as necessary.
5) Boot the system kernel with the boot parameter "crashkernel=Y@X", where Y specifies how much memory to reserve for the dump-capture kernel and X specifies the beginning of this reserved memory. For example, "crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory starting at physical address
0x01000000for the dump-capture kernel.
Most of this doesn't apply to powerpc.
Quoted 3 lines
On x86 and x86_64, use "crashkernel=64M@16M". On ppc64, use "crashkernel=128M@32M".
No just use "crashkernel=128M".
Quoted 14 lines
The dump-capture kernel
-----------------------1) Under "General setup," append "-kdump" to the current string in "Local version."
2) On x86, enable high memory support under "Processor type and features":
CONFIG_HIGHMEM=y3) On x86 and
x86_64, disable symmetric multi-processing support under "Processor type and features":
Quoted 7 lines
CONFIG_SMP=n4) On ppc64, disable NUMA support and enable EMBEDDED support:
CONFIG_NUMA=n
CONFIG_EMBEDDED=y
CONFIG_EEH=Nfor the dump-capture kernel
Why are we disabling NUMA? AFAIK we work on more systems with NUMA than without?
And why are we turning off EMBEDDED and EEH?
Quoted 11 lines
5) Enable "kernel crash dumps" support under "Processor type and features":
CONFIG_CRASH_DUMP=y6) Use a suitable value for "Physical address where the kernel is loaded" (under "Processor type and features"). This only appears when "kernel crash dumps" is enabled. By default this value is
0x1000000(16MB). It should be the same as X in the "crashkernel=Y@X" boot parameter discussed above.
Quoted 4 lines
On x86 and
x86_64, use "CONFIG_PHYSICAL_START=0x1000000".On ppc64 the value is automatically set at 32MB when
CONFIG_CRASH_DUMPis set.
This whole step should start "On x86 ..."
Quoted 2 lines
6) Optionally enable "
/proc/vmcoresupport" under "Filesystems" -> "Pseudo filesystems".
6 + 1 = 6 :D
Quoted 9 lines
CONFIG_PROC_VMCORE=y7) Make and install the kernel and its modules. DO NOT add this kernel to the boot loader configuration files.
Load the Dump-capture Kernel
============================
Quoted 6 lines
After booting to the system kernel, load the dump-capture kernel using the following command:
kexec -p <dump-capture-kernel> \ --initrd=<initrd-for-dump-capture-kernel> --args-linux \ --append="root=<root-dev> init 1 irqpoll"
I've never tested irqpoll on powerpc, I'm not sure we want to recommend it, has someone tested it?
Quoted 88 lines
Notes on loading the dump-capture kernel:
* <dump-capture-kernel> must be a vmlinux image (that is, an uncompressed ELF image). bzImage does not work at this time.
* By default, the ELF headers are stored in ELF64 format to support systems with more than 4GB memory. The --elf32-core-headers option can be used to force the generation of ELF32 headers. This is necessary because GDB currently cannot open vmcore files with ELF64 headers on 32-bit systems. ELF32 headers can be used on non-PAE systems (that is, less than 4GB of memory).
* The "irqpoll" boot parameter reduces driver initialization failures due to shared interrupts in the dump-capture kernel.
* You must specify <root-dev> in the format corresponding to the root device name in the output of mount command.
* "init 1" boots the dump-capture kernel into single-user mode without networking. If you want networking, use "init 3."
Kernel Panic
============After successfully loading the dump-capture kernel as previously described, the system will reboot into the dump-capture kernel if a panic occurs. You can write a module to force the panic, or use "ALT-SysRq-c" to initiate a crash dump for testing purposes.
Write Out the Dump File
=======================After the dump-capture kernel is booted, write out the dump file with the following command:
cp
/proc/vmcore<dump-file>You can also access dumped memory as a
/dev/oldmemdevice for a linear and raw view. To create the device, use the following command:mknod
/dev/oldmemc 1 12Use the dd command with suitable options for count, bs, and skip to access specific portions of the dump.
To see the entire memory, use the following command:
dd if=/dev/oldmem of=oldmem.001Analysis
========Before analyzing the dump image, you should reboot into a stable kernel.
You can do limited analysis using GDB on the dump file copied out of
/proc/vmcore. Use the debug vmlinux built with -g and run the following command:gdb vmlinux <dump-file>
Stack trace for the task on processor 0, register display, and memory display work fine.
Note: GDB cannot analyze core files generated in ELF64 format for x86. On systems with a maximum of 4GB of memory, you can generate ELF32-format headers using the --elf32-core-headers kernel option on the dump kernel.
You can also use the Crash utility to analyze dump files in Kdump format. Crash is available on Dave Anderson's site at the following URL:
http://people.redhat.com/~anderson/
To Do
=====1) Provide a kernel pages filtering mechanism, so core file size is not extreme on systems with huge memory banks.
2) Relocatable kernel can help in maintaining multiple kernels for
crash_dump, and the same kernel as the system kernel can be used to capture the dump.
Quoted 5 lines
Contact
=======Vivek Goyal ([email protected])
Maneesh Soni ([email protected])
cheers
Signature · 8 lines
Michael Ellerman IBM OzLabs wwweb: http://michael.ellerman.id.au phone: +61 2 6212 1183 (tie line 70 21183) We do not inherit the earth from our ancestors, we borrow it from our children. - S.M.A.R.T Person
Quoted 158 lines · Michael Ellerman
Hi David,
Nice work. Few comments below ...
Quoted 19 lines · David Wilder
Attached is a updated
Documentation/kdump/kdump.txt. Please provide comments. I will incorporate your feedback and send up to Linus.plain text document attachment (kdump-final-20060425.txt)
================================================================
Documentation for Kdump - The kexec-based Crash Dumping Solution
================================================================This document includes overview, setup and installation, and analysis information.
Overview
========Kdump uses kexec to quickly boot to a dump-capture kernel whenever a dump of the system kernel's memory needs to be taken (for example, when the system panics). The system kernel's memory image is preserved across the reboot and is accessible to the dump-capture kernel.
Quoted 6 lines
You can use common Linux commands, such as cp and scp, to copy the memory image to a dump file on the local disk, or across the network to a remote system.
Kdump and kexec are currently supported on the x86,
x86_64, and ppc64 architectures.s/ppc64/64-bit powerpc/ ?
Quoted 5 lines
When the system kernel boots, it reserves a small section of memory for the dump-capture kernel. This ensures that ongoing Direct Memory Access (DMA) from the system kernel does not corrupt the dump-capture kernel. The kexec -p command loads the dump-capture kernel into this reserved memory.
Well hopefully ;)
Quoted 89 lines
On x86 machines, the first 640 KB of physical memory is needed to boot, regardless of where the kernel loads. Therefore, kexec backs up this region just before rebooting into the dump-capture kernel.
All of the necessary information about the system kernel's core image is encoded in the ELF format, and stored in a reserved area of memory before a crash. The physical address of the start of the ELF header is passed to the dump-capture kernel through the elfcorehdr= boot parameter.
With the dump-capture kernel, you can access the memory image, or "old memory," in two ways:
- Through a
/dev/oldmemdevice interface. A capture utility can read the device file and write out the memory in raw format. This is a raw dump of memory. Analysis and capture tools must be intelligent enough to determine where to look for the right information.- Through
/proc/vmcore. This exports the dump as an ELF-format file that you can write out using file copy commands such as cp or scp. Further, you can use analysis tools such as the GNU Debugger (GDB) and the Crash tool to debug the dump file. This method ensures that the dump pages are correctly ordered.Setup and Installation
======================Install kexec-tools and the Kdump patch
---------------------------------------1) Login as the root user.
2) Download the kexec-tools user-space package from the following URL:
http://www.xmission.com/~ebiederm/files/kexec/kexec-tools-1.101.tar.gz3) Unpack the tarball with the tar command, as follows:
tar xvpzf kexec-tools-1.101.tar.gz4) Download the latest consolidated Kdump patch from the following URL:
http://lse.sourceforge.net/kdump/
(This location is being used until all the user-space Kdump patches are integrated with the kexec-tools package.)
5) Change to the kexec-tools-1.101 directory, as follows:
cd kexec-tools-1.1016) Apply the consolidated patch to the kexec-tools-1.101 source tree with the patch command, as follows. (Modify the path to the downloaded patch as necessary.)
patch -p1 < /path-to-kdump-patch/kexec-tools-1.101-kdump.patch7) Configure the package, as follows:
./configure
8) Compile the package, as follows:
make
9) Install the package, as follows:
make install
Download and build the system and dump-capture kernels
------------------------------------------------------Download the mainline (vanilla) kernel source code (2.6.13-rc1 or newer) from http://www.kernel.org. Two kernels must be built: a system kernel and a dump-capture kernel. Use the following steps to configure these kernels with the necessary kexec and Kdump features:
System kernel
-------------1) Enable "kexec system call" in "Processor type and features."
CONFIG_KEXEC=y2) Enable "sysfs file system support" in "Filesystem" -> "Pseudo filesystems." This is usually enabled by default.
Quoted 8 lines
CONFIG_SYSFS=yNote that "sysfs file system support" might not appear in the "Pseudo filesystems" menu if "Configure standard kernel features (for small systems)" is not enabled in "General Setup." In this case, check the .config file itself to ensure that sysfs is turned on, as follows:
grep '
CONFIG_SYSFS' .configIs there a particular requirement for sysfs?
Quoted 8 lines
3) Enable "Compile the kernel with debug info" in "Kernel hacking."
CONFIG_DEBUG_INFO=YThis causes the kernel to be built with debug symbols. The dump analysis tools require a vmlinux with debug symbols in order to read and analyze a dump file.
Quoted 8 lines
4) Make and install the kernel and its modules. Update the boot loader (such as grub, yaboot, or lilo) configuration files as necessary.
5) Boot the system kernel with the boot parameter "crashkernel=Y@X", where Y specifies how much memory to reserve for the dump-capture kernel and X specifies the beginning of this reserved memory. For example, "crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory starting at physical address
0x01000000for the dump-capture kernel.
Quoted 8 lines
Most of this doesn't apply to powerpc.
Quoted 3 lines
On x86 and x86_64, use "crashkernel=64M@16M". On ppc64, use "crashkernel=128M@32M".No just use "crashkernel=128M".
May be this is to follow the same convention in other architectures.
Quoted 18 lines
Quoted 18 lines
The dump-capture kernel
-----------------------1) Under "General setup," append "-kdump" to the current string in "Local version."
2) On x86, enable high memory support under "Processor type and features":
CONFIG_HIGHMEM=y3) On x86 and
x86_64, disable symmetric multi-processing support under "Processor type and features":
CONFIG_SMP=n4) On ppc64, disable NUMA support and enable EMBEDDED support:
Quoted 8 lines
Quoted 3 lines
CONFIG_NUMA=n
CONFIG_EMBEDDED=y
CONFIG_EEH=Nfor the dump-capture kernelWhy are we disabling NUMA? AFAIK we work on more systems with NUMA than without?
And why are we turning off EMBEDDED and EEH?
In some systems kdump with NUMA panics. Also EEH gives some oops while kdump booting. To disable EEH, we need to enable CONFIG_EMBEDDED
Quoted 157 lines
Quoted 11 lines
5) Enable "kernel crash dumps" support under "Processor type and features":
CONFIG_CRASH_DUMP=y6) Use a suitable value for "Physical address where the kernel is loaded" (under "Processor type and features"). This only appears when "kernel crash dumps" is enabled. By default this value is
0x1000000(16MB). It should be the same as X in the "crashkernel=Y@X" boot parameter discussed above.Quoted 4 lines
On x86 and
x86_64, use "CONFIG_PHYSICAL_START=0x1000000".On ppc64 the value is automatically set at 32MB when
CONFIG_CRASH_DUMPis set.This whole step should start "On x86 ..."
Quoted 2 lines
6) Optionally enable "
/proc/vmcoresupport" under "Filesystems" -> "Pseudo filesystems".6 + 1 = 6 :D
Quoted 9 lines
CONFIG_PROC_VMCORE=y7) Make and install the kernel and its modules. DO NOT add this kernel to the boot loader configuration files.
Load the Dump-capture Kernel
============================Quoted 6 lines
After booting to the system kernel, load the dump-capture kernel using the following command:
kexec -p <dump-capture-kernel> \ --initrd=<initrd-for-dump-capture-kernel> --args-linux \ --append="root=<root-dev> init 1 irqpoll"I've never tested irqpoll on powerpc, I'm not sure we want to recommend it, has someone tested it?
Quoted 88 lines
Notes on loading the dump-capture kernel:
* <dump-capture-kernel> must be a vmlinux image (that is, an uncompressed ELF image). bzImage does not work at this time.
* By default, the ELF headers are stored in ELF64 format to support systems with more than 4GB memory. The --elf32-core-headers option can be used to force the generation of ELF32 headers. This is necessary because GDB currently cannot open vmcore files with ELF64 headers on 32-bit systems. ELF32 headers can be used on non-PAE systems (that is, less than 4GB of memory).
* The "irqpoll" boot parameter reduces driver initialization failures due to shared interrupts in the dump-capture kernel.
* You must specify <root-dev> in the format corresponding to the root device name in the output of mount command.
* "init 1" boots the dump-capture kernel into single-user mode without networking. If you want networking, use "init 3."
Kernel Panic
============After successfully loading the dump-capture kernel as previously described, the system will reboot into the dump-capture kernel if a panic occurs. You can write a module to force the panic, or use "ALT-SysRq-c" to initiate a crash dump for testing purposes.
Write Out the Dump File
=======================After the dump-capture kernel is booted, write out the dump file with the following command:
cp
/proc/vmcore<dump-file>You can also access dumped memory as a
/dev/oldmemdevice for a linear and raw view. To create the device, use the following command:mknod
/dev/oldmemc 1 12Use the dd command with suitable options for count, bs, and skip to access specific portions of the dump.
To see the entire memory, use the following command:
dd if=/dev/oldmem of=oldmem.001Analysis
========Before analyzing the dump image, you should reboot into a stable kernel.
You can do limited analysis using GDB on the dump file copied out of
/proc/vmcore. Use the debug vmlinux built with -g and run the following command:gdb vmlinux <dump-file>
Stack trace for the task on processor 0, register display, and memory display work fine.
Note: GDB cannot analyze core files generated in ELF64 format for x86. On systems with a maximum of 4GB of memory, you can generate ELF32-format headers using the --elf32-core-headers kernel option on the dump kernel.
You can also use the Crash utility to analyze dump files in Kdump format. Crash is available on Dave Anderson's site at the following URL:
http://people.redhat.com/~anderson/
To Do
=====1) Provide a kernel pages filtering mechanism, so core file size is not extreme on systems with huge memory banks.
2) Relocatable kernel can help in maintaining multiple kernels for
crash_dump, and the same kernel as the system kernel can be used to capture the dump.Quoted 5 lines
Contact
=======Vivek Goyal ([email protected])
Maneesh Soni ([email protected])cheers
Signature · 15 lines
Michael Ellerman IBM OzLabs wwweb: http://michael.ellerman.id.au phone: +61 2 6212 1183 (tie line 70 21183) We do not inherit the earth from our ancestors, we borrow it from our children. - S.M.A.R.T Person _______________________________________________ Linuxppc-dev mailing list [email protected] https://ozlabs.org/mailman/listinfo/linuxppc-dev
Quoted 6 lines · Michael Ellerman
Quoted 6 lines
Load the Dump-capture Kernel
============================After booting to the system kernel, load the dump-capture kernel using the following command:
Quoted 7 lines
Quoted 3 lines
kexec -p <dump-capture-kernel> \ --initrd=<initrd-for-dump-capture-kernel> --args-linux \ --append="root=<root-dev> init 1 irqpoll"I've never tested irqpoll on powerpc, I'm not sure we want to recommend it, has someone tested it?
We have tested it on x86 & x86_64 and it works fine. Not sure about powerpc. Dave, Mohan and Mike have been doing some testing on powerpc. Guys any inputs?
-vivek