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.



Controls whether or not kdump-tools will take any action. If not set or 0, the kdump-tools init script will not run.


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


See sysctl(8) for more info.


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.


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.


Full path to a directory where the vmcore will be saved. Date stamped subdirectories are created each time a vmcore file is processed. If not set, /var/crash will be used.


This variable specifies a command to run if the vmcore save fails. If not set, no special action is taken.


A debug version of the running kernel. If not set, kdump-config will use /usr/lib/debug/vmlinux-$(uname-r) if it exists. Otherwise, kdump will still work, but the dump will take longer and will be much larger.


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.


Additional arguments to the kexec command used to load the kdump kernel.


Normally, the current kernel commandline is obtained from /proc/cmdline. Set this variable to override /proc/cmdline.


Additional arguments to append to the command line for the kdump kernel. If not set, “irqpoll maxcpus=1 nousb” will be used.


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


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.


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.


Architectural considerations


x86 && PAE && memory > 4 Gigabytes - use KDUMP_KEXEC_ARGS="--elf64-core-headers"


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.


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.



Boot Kernel Configuration - The boot kernel must be configured with CONFIG_KEXEC=y and, if it is also to be used as the kdump kernel, CONFIG_CRASHDUMP=y.

For ia64, only makedumpfile level 1 will work if the memory model selected is CONFIG_DISCONTIG. CONFIG_SPARSEMEM is recommended instead.


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_PHYSICAL_START. If the boot kernel is relocatable, kdump-tools will automatically use that kernel. Otherwise, a relocatable or relocated kernel will need to be provided. The kdump kernel can be specified in the /etc/default/kdump-tools file. Set the KDUMP_KERNEL 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


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 without - makedumpfile will still work, but the dumpfile will be larger and take longer to save to disk.


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:


This option starts a shell if kdump-tools cannot save the vmcore file:

KDUMP_FAIL_CMD="/bin/bash; reboot -f"



an init script to automatically load a kdump kernel, or save a vmcore and reboot.


the kdump-tools configuration file


a link to the current debug kernel


the last kexec_cmd executed by kdump-config


See kdump-config(8) for explanations of various error messages.

RELATED TO kdump-tools…



kdump-config(8), kexec(8), sysctl(8), makedumpfile(8), crash(8), gdb(1),


Terry Loftin <[email protected]>