kdump-tools.conf(5) Linux System Administrator's Manual kdump-tools.conf(5)
NAME
kdump-tools.conf - configuration file for the kdump-tools init script
SYNOPSIS
/etc/default/kdump-tools
DESCRIPTION
kdump-tools manages the kdump feature of the Linux kernel. The /etc/default/kdump-tools file contains local configuration settings of
kdump.
This file is sourced into a shell script, so it's format should be consistent with shell scripting.
OPTIONS
USE_KDUMP
Controls whether or not kdump-tools will take any action. If not set or 0, the kdump-tools init script will not run.
KDUMP_SYSCTL
Controls when a panic occurs, using the sysctl(8) interface. Each time a kdump kernel is loaded, "sysctl -w $KDUMP_SYSCTL" is also
executed, thus allowing the system adiminstrator to maintain customizable conditions for a kdump. The contents of this variable
should be the "variable=value ..." portion of the "sysctl -w" command. If not set, "kernel.panic_on_oops=1" will be used. This
feature can be disabled by setting
KDUMP_SYSCTL=" "
See sysctl(8) for more info.
KDUMP_KERNEL
A full pathname to a kdump kernel (the kernel that is kexec'd at crash time in a reserved memory area, exposing the old kernel's
memory for dumping). If not set, kdump-config will use the boot kernel as the kdump kernel if it is relocatable; otherwise you must
set KDUMP_KERNEL in order for kdump-tools to work.
KDUMP_INITRD
A full pathname to the kdump initrd (if used). If KDUMP_KERNEL is set and KDUMP_INITRD is not set, a warning message will be
printed, and an initrd will not be used.
KDUMP_COREDIR
Full path to a directory where the vmcore will be saved. Date stamped subdirectories are created each time a vmcore file is pro-
cessed. If not set, /var/crash will be used.
KDUMP_FAIL_CMD
This variable specifies a command to run if the vmcore save fails. If not set, no special action is taken.
DEBUG_KERNEL
A debug version of the running kernel. If not set, kdump-config will use /usr/lib/debug/vmlinux-$(uname-r) if it exists. Other-
wise, kdump will still work, but the dump will take longer and will be much larger.
MAKEDUMP_ARGS
Extra arguments passed to makedumpfile(8). If not set, "-c -d 31" will be used. This tells makedumpfile to use compression, and
reduce the corefile to in-use kernel pages only. See makedumpfile(8) for details.
KDUMP_KEXEC_ARGS
Additional arguments to the kexec command used to load the kdump kernel.
KDUMP_CMDLINE
Normally, the current kernel commandline is obtained from /proc/cmdline. Set this variable to override /proc/cmdline.
KDUMP_CMDLINE_APPEND
Additional arguments to append to the command line for the kdump kernel. If not set, "irqpoll maxcpus=1 nousb" will be used.
USAGE
kdump-tools is as automated as can be at this point but there are some prerequisites to using it. Additionally, some manual configuration
is still required.
Manual Configuration
1. USE_KDUMP is set to 0 by default. To enable kdump-tools, edit the /etc/default/kdump-tools configuration file and set USE_KDUMP=1.
2. Kernel Command line parameters - the kernel must be booted with a crashkernel= command line parameter. Some example crashkernel
parameters:
ia64: crashkernel=384M
x86: crashkernel=128M
x86_64: crashkernel=256M
Some users may also want to add nmi_watchdog=1 on certain systems. The nmi watchdog will cause the kernel to panic (and kdump) if a
system hang is detected.
The kernel command line parameter is generally set in one of these files: /etc/default/grub, /boot/grub/menu.lst, /etc/elilo.conf,
or /etc/lilo.conf. If the command line parameter is changed, a reboot is required in order for it to take effect.
3. Architectural considerations
A) x86 && PAE && memory > 4 Gigabytes - use KDUMP_KEXEC_ARGS="--elf64-core-headers"
B) x86 and x86_64 - Some systems can take advantage of the nmi watchdog. Add nmi_watchdog=1 to the boot commandline to turn on
the watchdog. The nmi interrupt will call panic if activated.
C) ia64 - Some systems may need KDUMP_KEXEC_ARGS="--noio". Use this if the system hangs after a panic, but before the kdump
kernel begins to boot.
Prerequisites
1. Boot Kernel Configuration - The boot kernel must be configured with CONFIG_KEXEC=y and, if it is also to be used as the kdump ker-
nel, CONFIG_CRASHDUMP=y.
For ia64, only makedumpfile level 1 will work if the memory model selected is CONFIG_DISCONTIG. CONFIG_SPARSEMEM is recommended
instead.
2. Kdump Kernel Configuration - The kdump kernel must be relocated or relocatable. ia64 is relocatable by default, but x86, x86_64,
and powerpc must be built with CONFIG_RELOCATABLE=y. Other architectures may require a predermined start location via CONFIG_PHYSI-
CAL_START. If the boot kernel is relocatable, kdump-tools will automatically use that kernel. Otherwise, a relocatable or relo-
cated kernel will need to be provided. The kdump kernel can be specified in the /etc/default/kdump-tools file. Set the KDUMP_KER-
NEL variable and if necessary the KDUMP_INITRD variable to point to the provided kernel and its initrd.
The kdump kernel must be configured with: CONFIG_CRASH_DUMP=y
3. Debug Kernel - An uncompressed debug kernel should be provided in order for makedumpfile to process the vmcore file. Without a
debug kernel, the transfer process is reduced to using "makedumpfile -c -d 1". If /usr/lib/debug/vmlinux-$(uname -r) exists, kdump-
tools will automatically use that kernel.
Otherwise, A) set DEBUG_KERNEL in /etc/default/kdump-tools to point to a debug version of the currently booted kernel or B) do with-
out - makedumpfile will still work, but the dumpfile will be larger and take longer to save to disk.
EXAMPLES
Also panic and kdump on oom:
KDUMP_SYSCTL="kernel.panic_on_oops=1 vm.panic_on_oom=1"
Use this option on x86 systems with PAE and more than 4 gig of memory:
KDUMP_KEXEC_ARGS="--elf64-core-headers"
This option starts a shell if kdump-tools cannot save the vmcore file:
KDUMP_FAIL_CMD="/bin/bash; reboot -f"
FILES
/etc/init.d/kdump-tools an init script to automatically load a kdump kernel, or save a vmcore and reboot.
/etc/default/kdump-tools the kdump-tools configuration file
/var/crash/kernel_link a link to the current debug kernel
/var/crash/kexec_cmd the last kexec_cmd executed by kdump-config
DIAGNOSTICS
See kdump-config(8) for explanations of various error messages.
SEE ALSO
/usr/share/doc/kdump-tools/README
/usr/share/doc/kdump-tools/README.Debian
kdump-config(8), kexec(8), sysctl(8), makedumpfile(8), crash(8), gdb(1),
AUTHOR
Terry Loftin <terry.loftin@hp.com>
kdump-tools v1.1.3 April 2007 kdump-tools.conf(5)