diff options
Diffstat (limited to 'Documentation/admin-guide/kdump/kdump.rst')
| -rw-r--r-- | Documentation/admin-guide/kdump/kdump.rst | 290 |
1 files changed, 184 insertions, 106 deletions
diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst index ac7e131d2935..7b011eb116a7 100644 --- a/Documentation/admin-guide/kdump/kdump.rst +++ b/Documentation/admin-guide/kdump/kdump.rst @@ -2,7 +2,7 @@ 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 @@ -13,11 +13,11 @@ 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 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, +Kdump and kexec are currently supported on the x86, x86_64, ppc64, s390x, arm and arm64 architectures. When the system kernel boots, it reserves a small section of memory for @@ -26,13 +26,15 @@ the dump-capture kernel. This ensures that ongoing Direct Memory Access 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 @@ -46,14 +48,14 @@ passed to the dump-capture kernel through the elfcorehdr= boot 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 ====================== @@ -111,7 +113,7 @@ There are two possible methods of using Kdump. 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 architectures which support a relocatable kernel. As - of today, i386, x86_64, ppc64, ia64, arm and arm64 architectures support + of today, i386, x86_64, ppc64, arm and arm64 architectures support relocatable kernel. Building a relocatable kernel is advantageous from the point of view that @@ -125,9 +127,14 @@ dump-capture kernels for enabling kdump support. 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 2) Enable "sysfs file system support" in "Filesystem" -> "Pseudo filesystems." This is usually enabled by default:: @@ -135,9 +142,9 @@ System kernel config options 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:: + filesystems" menu if "Configure standard kernel features (expert users)" + 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 @@ -157,6 +164,10 @@ Dump-capture kernel config options (Arch Independent) CONFIG_CRASH_DUMP=y + And this will select VMCORE_INFO and CRASH_RESERVE:: + CONFIG_VMCORE_INFO=y + CONFIG_CRASH_RESERVE=y + 2) Enable "/proc/vmcore support" under "Filesystems" -> "Pseudo filesystems":: CONFIG_PROC_VMCORE=y @@ -169,23 +180,19 @@ 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 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. - (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 @@ -223,28 +230,6 @@ Dump-capture kernel config options (Arch Dependent, ppc64) Make and install the kernel and its modules. -Dump-capture kernel config options (Arch Dependent, ia64) ----------------------------------------------------------- - -- No specific options are required to create a dump-capture kernel - for ia64, other than those specified in the arch independent section - above. This means that it is possible to use the system kernel - 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, - or omitting it all together:: - - crashkernel=256M@0 - - or:: - - 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) ---------------------------------------------------------- @@ -260,54 +245,106 @@ Dump-capture kernel config options (Arch Dependent, arm64) 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 + +4) crashkernel=size,cma + Reserve additional crash kernel memory from CMA. This reservation is + usable by the first system's userspace memory and kernel movable + allocations (memory balloon, zswap). Pages allocated from this memory + range will not be included in the vmcore so this should not be used if + dumping of userspace memory is intended and it has to be expected that + some movable kernel pages may be missing from the dump. + + A standard crashkernel reservation, as described above, is still needed + to hold the crash kernel and initrd. + + This option increases the risk of a kdump failure: DMA transfers + configured by the first kernel may end up corrupting the second + kernel's memory. + + This reservation method is intended for systems that can't afford to + sacrifice enough memory for standard crashkernel reservation and where + less reliable and possibly incomplete kdump is preferable to no kdump at + all. + +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". - 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. - If use sparse memory, the size should be rounded to GRANULE boundaries. - On s390x, typically use "crashkernel=xxM". The value of xx is dependent on the memory consumption of the kdump system. In general this is not dependent on the memory size of the production system. @@ -331,17 +368,13 @@ 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. + - Use vmlinux if kernel is not relocatable. For ppc64: - Use vmlinux -For ia64: - - - Use vmlinux or vmlinuz.gz - For s390x: - Use image or bzImage @@ -383,16 +416,12 @@ to load dump-capture kernel:: --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. -For i386, x86_64 and ia64: +For i386 and x86_64: - "1 irqpoll maxcpus=1 reset_devices" + "1 irqpoll nr_cpus=1 reset_devices" For ppc64: @@ -400,7 +429,7 @@ For ppc64: For s390x: - "1 maxcpus=1 cgroup_disable=memory" + "1 nr_cpus=1 cgroup_disable=memory" For arm: @@ -408,7 +437,7 @@ For arm: For arm64: - "1 maxcpus=1 reset_devices" + "1 nr_cpus=1 reset_devices" Notes on loading the dump-capture kernel: @@ -440,10 +469,9 @@ Notes on loading the dump-capture kernel: to use multi-thread programs with it, such as parallel dump feature of makedumpfile. Otherwise, the multi-thread program may have a great performance degradation. To enable multi-cpu support, you should bring up an - SMP dump-capture kernel and specify maxcpus/nr_cpus, disable_cpu_apicid=[X] - options while loading it. + SMP dump-capture kernel and specify maxcpus/nr_cpus options while loading it. -* For s390x there are two kdump modes: If a ELF header is specified with +* For s390x there are two kdump modes: If an ELF header is specified with the elfcorehdr= kernel parameter, it is used by the kdump kernel as it is done on all other architectures. If no elfcorehdr= kernel parameter is specified, the s390x kdump kernel dynamically creates the header. The @@ -488,6 +516,14 @@ the following command:: cp /proc/vmcore <dump-file> +or use scp to write out the dump file between hosts on a network, e.g:: + + scp /proc/vmcore remote_username@remote_ip:<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 ======== @@ -509,9 +545,12 @@ 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: +format. Crash is available at the following URL: - http://people.redhat.com/~anderson/ + https://github.com/crash-utility/crash + +Crash document can be found at: + https://crash-utility.github.io/ Trigger Kdump on WARN() ======================= @@ -521,11 +560,50 @@ will cause a kdump to occur at the panic() call. In cases where a user wants to specify this during runtime, /proc/sys/kernel/panic_on_warn can be set to 1 to achieve the same behaviour. +Trigger Kdump on add_taint() +============================ + +The kernel parameter panic_on_taint facilitates a conditional call to panic() +from within add_taint() whenever the value set in this bitmask matches with the +bit flag being set by add_taint(). +This will cause a kdump to occur at the add_taint()->panic() call. + +Write the dump file to encrypted disk volume +============================================ + +CONFIG_CRASH_DM_CRYPT can be enabled to support saving the dump file to an +encrypted disk volume (only x86_64 supported for now). User space can interact +with /sys/kernel/config/crash_dm_crypt_keys for setup, + +1. Tell the first kernel what logon keys are needed to unlock the disk volumes, + # Add key #1 + mkdir /sys/kernel/config/crash_dm_crypt_keys/7d26b7b4-e342-4d2d-b660-7426b0996720 + # Add key #1's description + echo cryptsetup:7d26b7b4-e342-4d2d-b660-7426b0996720 > /sys/kernel/config/crash_dm_crypt_keys/description + + # how many keys do we have now? + cat /sys/kernel/config/crash_dm_crypt_keys/count + 1 + + # Add key #2 in the same way + + # how many keys do we have now? + cat /sys/kernel/config/crash_dm_crypt_keys/count + 2 + + # To support CPU/memory hot-plugging, re-use keys already saved to reserved + # memory + echo true > /sys/kernel/config/crash_dm_crypt_key/reuse + +2. Load the dump-capture kernel + +3. After the dump-capture kerne get booted, restore the keys to user keyring + echo yes > /sys/kernel/crash_dm_crypt_keys/restore + Contact ======= -- Vivek Goyal (vgoyal@redhat.com) -- Maneesh Soni (maneesh@in.ibm.com) +- kexec@lists.infradead.org GDB macros ========== |