Hi David, Nice work. Few comments below ...
On Wed, 2006-04-26 at 10:49 -0700, David Wilder wrote: > 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. > > 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/ ? > 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 ;) > 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/oldmem device 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.gz > > 3) Unpack the tarball with the tar command, as follows: > > tar xvpzf kexec-tools-1.101.tar.gz > > 4) 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-1.101 > > 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.) > > patch -p1 < /path-to-kdump-patch/kexec-tools-1.101-kdump.patch > > 7) 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=y > > 2) Enable "sysfs file system support" in "Filesystem" -> "Pseudo > filesystems." This is usually enabled by default. > > CONFIG_SYSFS=y > > Note 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? > 3) Enable "Compile the kernel with debug info" in "Kernel hacking." > > CONFIG_DEBUG_INFO=Y > > This 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. > > 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 "[EMAIL PROTECTED]", > where Y specifies how much memory to reserve for the dump-capture kernel > and X specifies the beginning of this reserved memory. For example, > "[EMAIL PROTECTED]" tells the system kernel to reserve 64 MB of memory > starting at physical address 0x01000000 for the dump-capture kernel. Most of this doesn't apply to powerpc. > On x86 and x86_64, use "[EMAIL PROTECTED]". > > On ppc64, use "[EMAIL PROTECTED]". No just use "crashkernel=128M". > 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=y > > 3) On x86 and x86_64, disable symmetric multi-processing support > under "Processor type and features": > > CONFIG_SMP=n > > 4) On ppc64, disable NUMA support and enable EMBEDDED support: > > CONFIG_NUMA=n > CONFIG_EMBEDDED=y > CONFIG_EEH=N for 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? > 5) Enable "kernel crash dumps" support under "Processor type and > features": > > CONFIG_CRASH_DUMP=y > > 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 "[EMAIL PROTECTED]" boot > parameter discussed above. > > On x86 and x86_64, use "CONFIG_PHYSICAL_START=0x1000000". > > On ppc64 the value is automatically set at 32MB when > CONFIG_CRASH_DUMP is set. This whole step should start "On x86 ..." > 6) Optionally enable "/proc/vmcore support" under "Filesystems" -> > "Pseudo filesystems". 6 + 1 = 6 :D > CONFIG_PROC_VMCORE=y > > 7) Make and install the kernel and its modules. DO NOT add this kernel > to the boot loader configuration files. > > > Load the Dump-capture Kernel > ============================ > > 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? > 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/oldmem device for a linear > and raw view. To create the device, use the following command: > > mknod /dev/oldmem c 1 12 > > Use 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.001 > > > Analysis > ======== > > 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. > > > Contact > ======= > > Vivek Goyal ([EMAIL PROTECTED]) > Maneesh Soni ([EMAIL PROTECTED]) [email protected] cheers -- 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
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