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Linux OS Service ‘kdump’

By admin

This is a script which configures kdump (kernel dump). Kdump provides a memory dump into a file named vmcore when the kernel has a critical issue. Vmcore is often required to investigate the issue. The crash dump is captured from the context of a freshly-booted kernel, not from the context of the crashed kernel. Kdump uses kexec to boot into a second kernel whenever the system crashes. Kexec is a fast-boot mechanism which allows rebooting a new Linux kernel from the context of a running kernel without going through any firmware or warm start.

Service Control

To manage the kdump service for future shutdowns and reboots, use the chkconfig tool:

# chkconfig kdump on
# chkconfig --list kdump
kdump           0:off   1:off   2:on    3:on    4:on    5:on    6:off

To control the kdump service immediately, use the service tool:

# service kdump
Usage: /etc/init.d/kdump {start|stop|status|restart|propagate}
# /etc/init.d/kdump start
Kdump already running                                      [  OK  ]
# /etc/init.d/kdump stop
Stopping kdump:                                            [  OK  ]

Package name:

kexec-tools-[version]-[arch].rpm
kexec-tools-2.0.0-310.el6.x86_64M

Configuration files

The default /etc/kdump.conf file is given below:

$ cat /etc/kdump.conf
# Configures where to put the kdump /proc/vmcore files
#
# This file contains a series of commands to perform (in order) when a
# kernel crash has happened and the kdump kernel has been loaded.  Directives in
# this file are only applicable to the kdump initramfs, and have no effect if
# the root filesystem is mounted and the normal init scripts are processed
#
# Currently only one dump target and path may be configured at a time. If dump
# to configured dump target fails, the default action will be preformed.
# Default action may be configured with the "default" directive below.
#
# Basics commands supported are:
# path  		- Append path to the filesystem device which you are
#			  dumping to.  Ignored for raw device dumps.
#		 	  If unset, will default to /var/crash.
#
# core_collector  
#			- This allows you to specify the command to copy the
#			  vmcore.  You could use the dump filtering program
#			  makedumpfile, the default one, to retrieve your core,
#			  which on some arches can drastically reduce core file
#			  size. See /usr/sbin/makedumpfile --help for a list of
#			  options. Note that the -i and -g options are not
#			  needed here, as the initrd will automatically be
#			  populated with a config file appropriate for the
#			  running kernel.
#			  For ssh dump, scp should be used instead of cp.
#
# raw 	- Will write /proc/vmcore into raw .
#
# nfs 	- Will mount fs and copy /proc/vmcore to
#			  //%HOST-%DATE/, supports DNS.
#
# nfs4       - Will use NFSv4 instead of NFSv3
#
# net        - This is a deprecated option to transfer vmcore over
#			  nfs.  Use "nfs" option instead.
#
# ssh 	- Will copy /proc/vmcore to
#			  :/%HOST-%DATE/ via SSH,
#			  supports DNS. If makedumpfile is the core_collector,
#			  it is piped to an "ssh" shell, otherwise use the
#			  specified core_collector like scp.
#			  NOTE: make sure user has necessary write
#			  permissions on server
#
# net      - This is a deprecated option to transfer vmcore over
#			  ssh.  Use "ssh" option instead.
#
#   - Will mount -t   /mnt and copy
#		 	  /proc/vmcore to /mnt//127.0.0.1-%DATE/.
#			  NOTE:  can be a device node, label or uuid.
#
# disk_timeout 
#			- Number of seconds to wait for disks to appear prior
#			  to continue to save dump. By default kdump waits
#			  180 seconds for the disks to show up it needs. This
#			  can be useful in some cases if disk never shows up
#			  (Either because disk was removed or because kdump is
#			  waiting on wrong disk).
#
# link_delay 
#			- Some network cards take a long time to initialize, and
#			  some spanning tree enabled networks do not transmit
#			  user traffic for long periods after a link state
#			  changes.  This optional parameter defines a wait
#			  period after a link is activated in which the
#			  initramfs will wait before attempting to transmit
#			  user data.
#
# kdump_post 
# 			- This directive allows you to run a specified
# 			  executable just after the memory dump process
# 			  terminates. The exit status from the dump process
# 			  is fed to the kdump_post executable, which can be
# 			  used to trigger different actions for success or
# 			  failure.
#
# kdump_pre 
#			- works just like the kdump_post directive, but instead
#			  of running after the dump process, runs immediately
#			  before.  Exit status of this binary is interpreted
#			  as follows:
#			  0 - continue with dump process as usual
#			  non 0 - reboot/halt the system
#
# extra_bins 
# 			- This directive allows you to specify additional
# 			  binaries or shell scripts you'd like to include in
# 			  your kdump initrd. Generally only useful in
# 			  conjunction with a kdump_post binary or script that
# 			  relies on other binaries or scripts.
#
# extra_modules 
# 			- This directive allows you to specify extra kernel
# 			  modules that you want to be loaded in the kdump
# 			  initrd, typically used to set up access to
# 			  non-boot-path dump targets that might otherwise
# 			  not be accessible in the kdump environment. Multiple
# 			  modules can be listed, separated by a space, and any
# 			  dependent modules will automatically be included.
# 			  Module name should be specified without ".ko" suffix.
#
# options  

Filed Under: Linux, Linux Services

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