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
+Kdump and kexec are currently supported on the x86, x86_64, ppc64 and ia64
architectures.
When the system kernel boots, it reserves a small section of memory for
regardless of where the kernel loads. Therefore, kexec backs up this
region just before rebooting into the dump-capture kernel.
+Similarly on PPC64 machines first 32KB of physical memory is needed for
+booting regardless of where the kernel is loaded and to support 64K page
+size kexec backs up the first 64KB memory.
+
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
Setup and Installation
======================
-Install kexec-tools and the Kdump patch
----------------------------------------
+Install kexec-tools
+-------------------
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.gz
-
-3) Unpack the tarball with the tar command, as follows:
-
- tar xvpzf kexec-tools-1.101.tar.gz
+http://www.kernel.org/pub/linux/kernel/people/horms/kexec-tools/kexec-tools-testing.tar.gz
-4) Download the latest consolidated Kdump patch from the following URL:
+This is a symlink to the latest version, which at the time of writing is
+20061214, the only release of kexec-tools-testing so far. As other versions
+are made released, the older onese will remain available at
+http://www.kernel.org/pub/linux/kernel/people/horms/kexec-tools/
- http://lse.sourceforge.net/kdump/
+Note: Latest kexec-tools-testing git tree is available at
- (This location is being used until all the user-space Kdump patches
- are integrated with the kexec-tools package.)
+git://git.kernel.org/pub/scm/linux/kernel/git/horms/kexec-tools-testing.git
+or
+http://www.kernel.org/git/?p=linux/kernel/git/horms/kexec-tools-testing.git;a=summary
-5) Change to the kexec-tools-1.101 directory, as follows:
+3) Unpack the tarball with the tar command, as follows:
- cd kexec-tools-1.101
+ tar xvpzf kexec-tools-testing.tar.gz
-6) 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.)
+4) Change to the kexec-tools directory, as follows:
- patch -p1 < /path-to-kdump-patch/kexec-tools-1.101-kdump.patch
+ cd kexec-tools-testing-VERSION
-7) Configure the package, as follows:
+5) Configure the package, as follows:
./configure
-8) Compile the package, as follows:
+6) Compile the package, as follows:
make
-9) Install the package, as follows:
+7) Install the package, as follows:
make install
-Download and build the system and dump-capture kernels
-------------------------------------------------------
+Build the system and dump-capture kernels
+-----------------------------------------
+There are two possible methods of using Kdump.
+
+1) Build a separate custom dump-capture kernel for capturing the
+ kernel core dump.
+
+2) Or use the system kernel binary itself as dump-capture kernel and there is
+ no need to build a separate dump-capture kernel. This is possible
+ only with the architecutres which support a relocatable kernel. As
+ of today i386 and ia64 architectures support relocatable kernel.
-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:
+Building a relocatable kernel is advantageous from the point of view that
+one does not have to build a second kernel for capturing the dump. But
+at the same time one might want to build a custom dump capture kernel
+suitable to his needs.
-System kernel
--------------
+Following are the configuration setting required for system and
+dump-capture kernels for enabling kdump support.
+
+System kernel config options
+----------------------------
1) Enable "kexec system call" in "Processor type and features."
analysis tools require a vmlinux with debug symbols in order to read
and analyze a dump file.
-4) Make and install the kernel and its modules. Update the boot loader
- (such as grub, yaboot, or lilo) configuration files as necessary.
+Dump-capture kernel config options (Arch Independent)
+-----------------------------------------------------
-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 0x01000000 for the dump-capture kernel.
-
- On x86 and x86_64, use "crashkernel=64M@16M".
+1) Enable "kernel crash dumps" support under "Processor type and
+ features":
- On ppc64, use "crashkernel=128M@32M".
+ CONFIG_CRASH_DUMP=y
+2) Enable "/proc/vmcore support" under "Filesystems" -> "Pseudo filesystems".
-The dump-capture kernel
------------------------
+ CONFIG_PROC_VMCORE=y
+ (CONFIG_PROC_VMCORE is set by default when CONFIG_CRASH_DUMP is selected.)
-1) Under "General setup," append "-kdump" to the current string in
- "Local version."
+Dump-capture kernel config options (Arch Dependent, i386 and x86_64)
+--------------------------------------------------------------------
-2) On x86, enable high memory support under "Processor type and
+1) On i386, enable high memory support under "Processor type and
features":
CONFIG_HIGHMEM64G=y
or
CONFIG_HIGHMEM4G
-3) On x86 and x86_64, disable symmetric multi-processing support
+2) On i386 and x86_64, disable symmetric multi-processing support
under "Processor type and features":
CONFIG_SMP=n
+
(If CONFIG_SMP=y, then specify maxcpus=1 on the kernel command line
when loading the dump-capture kernel, see section "Load the Dump-capture
Kernel".)
-4) On ppc64, disable NUMA support and enable EMBEDDED support:
+3) If one wants to build and use a relocatable kernel,
+ Enable "Build a relocatable kernel" support under "Processor type and
+ features"
- CONFIG_NUMA=n
- CONFIG_EMBEDDED=y
- CONFIG_EEH=N for the dump-capture kernel
+ CONFIG_RELOCATABLE=y
-5) Enable "kernel crash dumps" support under "Processor type and
- features":
+4) 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. A suitable value depends upon
+ whether kernel is relocatable or not.
+
+ If you are using a relocatable kernel use CONFIG_PHYSICAL_START=0x100000
+ This will compile the kernel for physical address 1MB, but given the fact
+ kernel is relocatable, it can be run from any physical address hence
+ kexec boot loader will load it in memory region reserved for dump-capture
+ kernel.
+
+ Otherwise it should be the start of memory region reserved for
+ second kernel using boot parameter "crashkernel=Y@X". Here X is
+ start of memory region reserved for dump-capture kernel.
+ Generally X is 16MB (0x1000000). So you can set
+ CONFIG_PHYSICAL_START=0x1000000
+
+5) Make and install the kernel and its modules. DO NOT add this kernel
+ to the boot loader configuration files.
- CONFIG_CRASH_DUMP=y
+Dump-capture kernel config options (Arch Dependent, ppc64)
+----------------------------------------------------------
-6) 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.
+* Make and install the kernel and its modules. DO NOT add this kernel
+ to the boot loader configuration files.
- On x86 and x86_64, use "CONFIG_PHYSICAL_START=0x1000000".
+Dump-capture kernel config options (Arch Dependent, ia64)
+----------------------------------------------------------
- On ppc64 the value is automatically set at 32MB when
- CONFIG_CRASH_DUMP is set.
+- No specific options are required to create a dump-capture kernel
+ for ia64, other than those specified in the arch idependent section
+ above. This means that it is possible to use the system kernel
+ as a dump-capture kernel if desired.
-6) Optionally enable "/proc/vmcore support" under "Filesystems" ->
- "Pseudo filesystems".
+ The crashkernel region can be automatically placed by the system
+ kernel at run time. This is done by specifying the base address as 0,
+ or omitting it all together.
- CONFIG_PROC_VMCORE=y
- (CONFIG_PROC_VMCORE is set by default when CONFIG_CRASH_DUMP is selected.)
+ crashkernel=256M@0
+ or
+ crashkernel=256M
-7) Make and install the kernel and its modules. DO NOT add this kernel
- to the boot loader configuration files.
+ If the start address is specified, note that the start address of the
+ kernel will be aligned to 64Mb, so if the start address is not then
+ any space below the alignment point will be wasted.
+
+
+Boot into System Kernel
+=======================
+
+1) Update the boot loader (such as grub, yaboot, or lilo) configuration
+ files as necessary.
+
+2) 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 0x01000000 (16MB) for the dump-capture kernel.
+ On x86 and x86_64, use "crashkernel=64M@16M".
+
+ On ppc64, use "crashkernel=128M@32M".
+
+ On ia64, 256M@256M is a generous value that typically works.
+ The region may be automatically placed on ia64, see the
+ dump-capture kernel config option notes above.
Load the Dump-capture Kernel
============================
-After booting to the system kernel, load the dump-capture kernel using
-the following command:
+After booting to the system kernel, dump-capture kernel needs to be
+loaded.
- kexec -p <dump-capture-kernel> \
+Based on the architecture and type of image (relocatable or not), one
+can choose to load the uncompressed vmlinux or compressed bzImage/vmlinuz
+of dump-capture kernel. Following is the summary.
+
+For i386 and x86_64:
+ - Use vmlinux if kernel is not relocatable.
+ - Use bzImage/vmlinuz if kernel is relocatable.
+For ppc64:
+ - Use vmlinux
+For ia64:
+ - Use vmlinux or vmlinuz.gz
+
+
+If you are using a uncompressed vmlinux image then use following command
+to load dump-capture kernel.
+
+ kexec -p <dump-capture-kernel-vmlinux-image> \
--initrd=<initrd-for-dump-capture-kernel> --args-linux \
- --append="root=<root-dev> init 1 irqpoll"
+ --append="root=<root-dev> <arch-specific-options>"
+If you are using a compressed bzImage/vmlinuz, then use following command
+to load dump-capture kernel.
-Notes on loading the dump-capture kernel:
+ kexec -p <dump-capture-kernel-bzImage> \
+ --initrd=<initrd-for-dump-capture-kernel> \
+ --append="root=<root-dev> <arch-specific-options>"
+
+Please note, that --args-linux does not need to be specified for ia64.
+It is planned to make this a no-op on that architecture, but for now
+it should be omitted
+
+Following are the arch specific command line options to be used while
+loading dump-capture kernel.
-* <dump-capture-kernel> must be a vmlinux image (that is, an
- uncompressed ELF image). bzImage does not work at this time.
+For i386, x86_64 and ia64:
+ "1 irqpoll maxcpus=1"
+
+For ppc64:
+ "1 maxcpus=1 noirqdistrib"
+
+
+Notes on loading the dump-capture kernel:
* 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).
+ systems with more than 4GB memory. On i386, kexec automatically checks if
+ the physical RAM size exceeds the 4 GB limit and if not, uses ELF32.
+ So, on non-PAE systems, ELF32 is always used.
+
+ 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.
* 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."
+* Boot parameter "1" boots the dump-capture kernel into single-user
+ mode without networking. If you want networking, use "3".
+* We generally don' have to bring up a SMP kernel just to capture the
+ dump. Hence generally it is useful either to build a UP dump-capture
+ kernel or specify maxcpus=1 option while loading dump-capture kernel.
Kernel Panic
============
is called inside interrupt context or die() is called and panic_on_oops is set,
the system will boot into the dump-capture kernel.
-On powererpc systems when a soft-reset is generated, die() is called by all cpus and the system system will boot into the dump-capture kernel.
+On powererpc systems when a soft-reset is generated, die() is called by all cpus
+and the system will boot into the dump-capture kernel.
For testing purposes, you can trigger a crash by using "ALT-SysRq-c",
-"echo c > /proc/sysrq-trigger or write a module to force the panic.
+"echo c > /proc/sysrq-trigger" or write a module to force the panic.
Write Out the Dump File
=======================
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.
+1) Provide relocatable kernels for all architectures to help in maintaining
+ multiple kernels for crash_dump, and the same kernel as the system kernel
+ can be used to capture the dump.
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