kdump.conf(5) centos man page

KDUMP.CONF(5) File Formats Manual KDUMP.CONF(5)

NAME
kdump.conf - configuration file for kdump kernel.

DESCRIPTION
kdump.conf is a configuration file for the kdump kernel crash collection service.

kdump.conf provides post-kexec instructions to the kdump kernel. It is stored in the initrd file managed by the kdump service. If you
change this file and do not want to restart before it takes effect, restart the kdump service to rebuild to initrd.

For most configurations, you can simply review the examples provided in the stock /etc/kdump.conf.

NOTE: For filesystem dump the dump target must be mounted before building kdump initramfs.

kdump.conf only affects the behavior of the initramfs. Please read the kdump operational flow section of kexec-kdump-howto.txt in the docs
to better understand how this configuration file affects the behavior of kdump.

OPTIONS
raw <partition>
Will dd /proc/vmcore into <partition>. Use persistent device names for partition devices, such as /dev/vg/<devname>.

nfs <nfs mount>
Will mount fs and copy /proc/vmcore to <mnt>/var/crash/%HOST-%DATE/, supports DNS. Note that a fqdn should be used as the server
name in the mount point

ssh <user@server>
Will scp /proc/vmcore to <user@server>:/var/crash/%HOST-%DATE/, supports DNS. NOTE: make sure user has necessary write permissions
on server and that a fqdn is used as the server name

sshkey <path>
Specifies the path of the ssh key you want to use when do ssh dump, the default value is /root/.ssh/kdump_id_rsa.

<fs type> <partition>
Will mount -t <fs type> <partition> /mnt and copy /proc/vmcore to /mnt/var/crash/%DATE/. NOTE: <partition> can be a device node,
label or uuid. It's recommended to use persistent device names such as /dev/vg/<devname>. Otherwise it's suggested to use label or
uuid.

path <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 <command> <options>
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 /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.

Note 1: About default core collector: Default core_collector for raw/ssh dump is: "makedumpfile -F -l --message-level 1 -d 31".
Default core_collector for other targets is: "makedumpfile -l --message-level 1 -d 31". Even if core_collector option is commented
out in kdump.conf, makedumpfile is default core collector and kdump uses it internally. If one does not want makedumpfile as
default core_collector, then they need to specify one using core_collector option to change the behavior.

Note 2: If "makedumpfile -F" is used then you will get a flattened format vmcore.flat, you will need to use "makedumpfile -R" to
rearrange the dump data from stdard input to a normal dumpfile (readable with analysis tools). ie. "makedumpfile -R vmcore <
vmcore.flat"

kdump_post <binary | script>
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.

Note that scripts written for use with this directive must use the /bin/bash interpreter

kdump_pre <binary | script>
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 the system

Note that scripts written for this directive must use the /bin/bash interpreter

extra_bins <binaries | shell scripts>
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 <module(s)>
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.

default <reboot | halt | poweroff | shell | dump_to_rootfs>
Action to preform in case dumping to intended target fails. If no default action is specified, "reboot" is assumed default. reboot:
If the default action is reboot simply reboot the system (this is what most people will want, as it returns the system to a nominal
state). shell: If the default action is shell, then drop to an shell session inside the initramfs from where you can manually pre-
form additional recovery actions. Exiting this shell reboots the system. halt: bring the system to a halt, requiring manual reset
poweroff: The system will be powered down. dump_to_rootfs:If the default action is dump_to_rootfs, specified root will be mounted
and dump will be saved in "path" directory. Note: kdump uses bash as the default shell.

force_rebuild <0 | 1>
By default, kdump initrd only will be rebuilt when necessary. Specify 1 to force rebuilding kdump initrd every time when kdump ser-
vice starts.

override_resettable <0 | 1>
Usually a unresettable block device can't be dump target. Specifying 1 means though block target is unresettable, user understand
this situation and want to try dumping. By default, it's set to 0, means not to try a destined failure.

dracut_args <arg(s)>
Kdump uses dracut to generate initramfs for second kernel. This option allows a user to pass arguments to dracut directly.

DEPRECATED OPTIONS
net <nfs mount>|<user@server>
net option is replaced by nfs and ssh options. Use nfs or ssh options directly.

options <module> <option list>
Use KDUMP_COMMANDLINE_APPEND in /etc/sysconfig/kdump to add proper module option as kernel command line params. Such as append
loop.max_loop=1 to limit maximum loop devices to 1.

link_delay <seconds>
link_delay was used to wait a network device to initialize before using it. Now dracut network module take care of this issue auto-
maticlly.

disk_timeout <seconds>
Similar to link_delay, dracut ensures disks being ready before kdump uses them.

debug_mem_level <0-3>
This was used to turns on debug/verbose output of kdump scripts regarding free/used memory at various points of execution. This
feature has been moved to dracut now. Use KDUMP_COMMANDLINE_APPEND in /etc/sysconfig/kdump and append dracut cmdline param
rd.memdebug=[0-3] to enable the debug output.

Higher level means more debugging output.

0 - no output

1 - partial /proc/meminfo

2 - /proc/meminfo

3 - /proc/meminfo + /proc/slabinfo

blacklist <list of kernel modules>
blacklist option was recently being used to prevent loading modules in initramfs. General terminology for blacklist has been that
module is present in initramfs but it is not actually loaded in kernel. Hence retaining blacklist option creates more confusing
behavior. It has been deprecated.

Instead use rd.driver.blacklist option on second kernel to blacklist a certain module. One can edit /etc/sysconfig/kdump.conf and
edit KDUMP_COMMANDLINE_APPEND to pass kernel command line options. Refer to dracut.cmdline man page for more details on module
blacklist option.

EXAMPLES
Here is some examples for core_collector option:

Core collector command format depends on dump target type. Typically for filesystem (local/remote), core_collector should accept two argu-
ments. First one is source file and second one is target file. For ex.

ex1. core_collector "cp --sparse=always"

Above will effectively be translated to:

cp --sparse=always /proc/vmcore <dest-path>/vmcore

ex2. core_collector "makedumpfile -l --message-level 1 -d 31"

Above will effectively be translated to:

makedumpfile -l --message-level 1 -d 31 /proc/vmcore <dest-path>/vmcore

For dump targets like raw and ssh, in general, core collector should expect one argument (source file) and should output the processed core
on standard output (There is one exception of "scp", discussed later). This standard output will be saved to destination using appropriate
commands.

raw dumps examples:

ex3. core_collector "cat"