the system panics). The system kernel's memory image is preserved across
the reboot and is accessible to the dump-capture kernel.
-You can use common Linux commands, such as cp and scp, to copy the
+You can use common 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.
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
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
+are released, the older ones will remain available at
http://www.kernel.org/pub/linux/kernel/people/horms/kexec-tools/
Note: Latest kexec-tools-testing git tree is available at
CONFIG_PROC_VMCORE=y
(CONFIG_PROC_VMCORE is set by default when CONFIG_CRASH_DUMP is selected.)
-Dump-capture kernel config options (Arch Dependent, i386)
---------------------------------------------------------
-1) On x86, enable high memory support under "Processor type and
+Dump-capture kernel config options (Arch Dependent, i386 and x86_64)
+--------------------------------------------------------------------
+
+1) On i386, enable high memory support under "Processor type and
features":
CONFIG_HIGHMEM64G=y
or
CONFIG_HIGHMEM4G
-2) 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
5) Make and install the kernel and its modules. DO NOT add this kernel
to the boot loader configuration files.
-Dump-capture kernel config options (Arch Dependent, x86_64)
-----------------------------------------------------------
-1) On x86 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".)
-
-2) 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.
-
- For x86_64, normally "CONFIG_PHYSICAL_START=0x1000000".
-
-3) Make and install the kernel and its modules. DO NOT add this kernel
- to the boot loader configuration files.
-
Dump-capture kernel config options (Arch Dependent, ppc64)
----------------------------------------------------------
-- Make and install the kernel and its modules. DO NOT add this kernel
+* Make and install the kernel and its modules. DO NOT add this kernel
to the boot loader configuration files.
Dump-capture kernel config options (Arch Dependent, ia64)
any space below the alignment point will be wasted.
+Extended crashkernel syntax
+===========================
+
+While the "crashkernel=size[@offset]" syntax is sufficient for most
+configurations, sometimes it's handy to have the reserved memory dependent
+on the value of System RAM -- that's mostly for distributors that pre-setup
+the kernel command line to avoid a unbootable system after some memory has
+been removed from the machine.
+
+The syntax is:
+
+ crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
+ range=start-[end]
+
+For example:
+
+ crashkernel=512M-2G:64M,2G-:128M
+
+This would mean:
+
+ 1) if the RAM is smaller than 512M, then don't reserve anything
+ (this is the "rescue" case)
+ 2) if the RAM size is between 512M and 2G, then reserve 64M
+ 3) if the RAM size is larger than 2G, then reserve 128M
+
+
Boot into System Kernel
=======================
-1) Make and install the kernel and its modules. Update the boot loader
- (such as grub, yaboot, or lilo) configuration files as necessary.
+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
can choose to load the uncompressed vmlinux or compressed bzImage/vmlinuz
of dump-capture kernel. Following is the summary.
-For i386:
+For i386 and x86_64:
- Use vmlinux if kernel is not relocatable.
- Use bzImage/vmlinuz if kernel is relocatable.
-For x86_64:
- - Use vmlinux
For ppc64:
- Use vmlinux
For ia64:
loading dump-capture kernel.
For i386, x86_64 and ia64:
- "init 1 irqpoll maxcpus=1"
+ "1 irqpoll maxcpus=1 reset_devices"
For ppc64:
- "init 1 maxcpus=1 noirqdistrib"
+ "1 maxcpus=1 noirqdistrib reset_devices"
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
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 will boot into the dump-capture kernel.
+On powerpc 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.
Contact
Vivek Goyal (vgoyal@in.ibm.com)
Maneesh Soni (maneesh@in.ibm.com)
-
-Trademark
-=========
-
-Linux is a trademark of Linus Torvalds in the United States, other
-countries, or both.
git.openpandora.org / pandora-kernel.git / blobdiff