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kdump-tools.conf(5) Linux System Administrator's Manual kdump-tools.conf(5)


kdump-tools.conf - configuration file for the kdump-tools init script




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.
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.
This variable controls if the dmesg buffer is dumped. If not set or set to 1, the dmesg buffer is dumped. If set to 0, the dmesg buffer is not dumped.
This variable specifies how many dump files should be kept on the local machine. If not set or set to 0, no special action is taken. If set to >1 and there are too many dump files on the machine, older dumps are removed. The cleanup action is only taken after a successful dump. This variable is ignored if remote dumping is enabled.
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, “reset_devices systemd.unit=kdump-tools-dump.service nr_cpus=1 irqpoll usbcore.nousb” will be used.
username and hostname of the remote server that will receive the dump and dmesg files. username@hostname format must be used.
Full path of the ssh private key to be used to login to the remote server. Use “kdump-config propagate” to send the public key to the remote server. If not set, the default /root/.ssh/kdump_id_rsa will be used
Select if hostname of IP address will be used as a prefix to the timestamped directory when sending files to the remote server. If not set, “ip” will be used.
Hostname and mount point of the NFS server configured to receive the crash dump. The syntax must be HOSTNAME:MOUNTPOINT (e.g. remote:/var/crash )


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.

By default, kernel dumps are stored locally on the system. kdump-tools can be configured to store the kernel dumps on a remote server accessible through the network.

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.

Networked kernel dump Configuration

Either use SSH or NFS to choose which protocol to use to remotely access the target server.
For SSH username@hostname needs to be provided along with an appropriate SSH_KEY definition or use “kdump-config propagate” to propagate a new default ssh key.
For NFS the remote server name must be provided along with the directory where files are to be copied.


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


Currently kdump-tools automatically sets the kernel sysctl for panic on oops, in order to collect a dump in this case. If the users want more panic triggers, like panic on OOM, or when a NMI is detected, it's recommended that they edit the sysctl configuration files (/etc/sysctl.conf or files on /etc/sysctl.d) in order to do so, and/or apply the sysctl settings with sysctl tool.

Sysctl handling *during a kdump*

kdump-tools allows users to configure sysctls overrides on kdump environment; this is specially useful to prevent sysctls from the regular boot to mess with the resource-impaired kdump environment.

The mechanism is restricted to kdump boot and will not affect regular boots. In order to add overrides, user should edit the file /etc/kdump/sysctl.conf.

By default, hugepages overrides are set and is highly recommended to keep them in the file, to prevent kdump out-of-memory conditions.


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
kdump-tools sysctl override 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.


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


Terry Loftin <>

Jul 2020 kdump-tools v1.6.7-2