Documentation for Kdump - The kexec-based Crash Dumping Solution
================================================================
-This document includes overview, setup and installation, and analysis
+This document includes overview, setup, installation, and analysis
information.
Overview
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 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.
+You can use common commands, such as cp, scp or makedumpfile 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, ppc64, ia64,
s390x, arm and arm64 architectures.
The kexec -p command loads the dump-capture kernel into this reserved
memory.
-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.
+On x86 machines, the first 640 KB of physical memory is needed for boot,
+regardless of where the kernel loads. For simpler handling, the whole
+low 1M is reserved to avoid any later kernel or device driver writing
+data into this area. Like this, the low 1M can be reused as system RAM
+by kdump kernel without extra handling.
-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.
+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.
For s390x, when kdump is triggered, the crashkernel region is exchanged
with the region [0, crashkernel region size] and then the kdump kernel
parameter. Optionally the size of the ELF header can also be passed
when using the elfcorehdr=[size[KMG]@]offset[KMG] syntax.
-
With the dump-capture kernel, you can access the memory image 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.
-
+write out using file copy commands such as cp or scp. You can also use
+makedumpfile utility to analyze and write out filtered contents with
+options, e.g with '-d 31' it will only write out kernel data. 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
======================
System kernel config options
----------------------------
-1) Enable "kexec system call" in "Processor type and features."::
+1) Enable "kexec system call" or "kexec file based system call" in
+ "Processor type and features."::
+
+ CONFIG_KEXEC=y or CONFIG_KEXEC_FILE=y
+
+ And both of them will select KEXEC_CORE::
- CONFIG_KEXEC=y
+ CONFIG_KEXEC_CORE=y
+
+ Subsequently, CRASH_CORE is selected by KEXEC_CORE::
+
+ CONFIG_CRASH_CORE=y
2) Enable "sysfs file system support" in "Filesystem" -> "Pseudo
filesystems." This is usually enabled by default::
CONFIG_HIGHMEM4G
-2) On i386 and x86_64, disable symmetric multi-processing support
- under "Processor type and features"::
+2) With CONFIG_SMP=y, usually nr_cpus=1 need specified on the kernel
+ command line when loading the dump-capture kernel because one
+ CPU is enough for kdump kernel to dump vmcore on most of systems.
- CONFIG_SMP=n
+ However, you can also specify nr_cpus=X to enable multiple processors
+ in kdump kernel. In this case, "disable_cpu_apicid=" is needed to
+ tell kdump kernel which cpu is 1st kernel's BSP. Please refer to
+ admin-guide/kernel-parameters.txt for more details.
- (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".)
+ With CONFIG_SMP=n, the above things are not related.
-3) If one wants to build and use a relocatable kernel,
- Enable "Build a relocatable kernel" support under "Processor type and
+3) A relocatable kernel is suggested to be built by default. If not yet,
+ enable "Build a relocatable kernel" support under "Processor type and
features"::
CONFIG_RELOCATABLE=y
as a dump-capture kernel if desired.
The crashkernel region can be automatically placed by the system
- kernel at run time. This is done by specifying the base address as 0,
+ kernel at runtime. This is done by specifying the base address as 0,
or omitting it all together::
crashkernel=256M@0
crashkernel=256M
- 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.
-
Dump-capture kernel config options (Arch Dependent, arm)
----------------------------------------------------------
on non-VHE systems even if it is configured. This is because the CPU
will not be reset to EL2 on panic.
-Extended crashkernel syntax
+crashkernel syntax
===========================
+1) crashkernel=size@offset
-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.
+ Here 'size' specifies how much memory to reserve for the dump-capture kernel
+ and 'offset' 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.
-The syntax is::
+ 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::
- crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
- range=start-[end]
+ crashkernel=256M@0
-For example::
+ or::
- crashkernel=512M-2G:64M,2G-:128M
+ crashkernel=256M
-This would mean:
+ If the start address is specified, note that the start address of the
+ kernel will be aligned to a value (which is Arch dependent), so if the
+ start address is not then any space below the alignment point will be
+ wasted.
- 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 (exclusive), then reserve 64M
- 3) if the RAM size is larger than 2G, then reserve 128M
+2) range1:size1[,range2:size2,...][@offset]
+ 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::
-Boot into System Kernel
-=======================
+ 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 (exclusive), then reserve 64M
+ 3) if the RAM size is larger than 2G, then reserve 128M
+
+3) crashkernel=size,high and crashkernel=size,low
+
+ If memory above 4G is preferred, crashkernel=size,high can be used to
+ fulfill that. With it, physical memory is allowed to be allocated from top,
+ so could be above 4G if system has more than 4G RAM installed. Otherwise,
+ memory region will be allocated below 4G if available.
+
+ When crashkernel=X,high is passed, kernel could allocate physical memory
+ region above 4G, low memory under 4G is needed in this case. There are
+ three ways to get low memory:
+
+ 1) Kernel will allocate at least 256M memory below 4G automatically
+ if crashkernel=Y,low is not specified.
+ 2) Let user specify low memory size instead.
+ 3) Specified value 0 will disable low memory allocation::
+
+ crashkernel=0,low
+
+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.
+2) Boot the system kernel with the boot parameter "crashkernel=Y@X".
- On x86 and x86_64, use "crashkernel=64M@16M".
+ On x86 and x86_64, use "crashkernel=Y[@X]". Most of the time, the
+ start address 'X' is not necessary, kernel will search a suitable
+ area. Unless an explicit start address is expected.
On ppc64, use "crashkernel=128M@32M".
For i386 and x86_64:
- - Use vmlinux if kernel is not relocatable.
- Use bzImage/vmlinuz if kernel is relocatable.
+ - Use vmlinux if kernel is not relocatable.
For ppc64:
For i386, x86_64 and ia64:
- "1 irqpoll maxcpus=1 reset_devices"
+ "1 irqpoll nr_cpus=1 reset_devices"
For ppc64:
For s390x:
- "1 maxcpus=1 cgroup_disable=memory"
+ "1 nr_cpus=1 cgroup_disable=memory"
For arm:
For arm64:
- "1 maxcpus=1 reset_devices"
+ "1 nr_cpus=1 reset_devices"
Notes on loading the dump-capture kernel:
cp /proc/vmcore <dump-file>
+You can also use makedumpfile utility to write out the dump file
+with specified options to filter out unwanted contents, e.g::
+
+ makedumpfile -l --message-level 1 -d 31 /proc/vmcore <dump-file>
Analysis
========
Contact
=======
-- Vivek Goyal (vgoyal@redhat.com)
-- Maneesh Soni (maneesh@in.ibm.com)
+- kexec@lists.infradead.org
GDB macros
==========
projects / users / hch / xfs.git / commitdiff