Linux Kernel Crash Dump

Introduction To Linux Kernel Crash Dump

A Linux kernel crash dump is a file that contains a snapshot of the kernel’s state at the time of a crash. It includes information about the kernel’s memory layout, active processes, and other system state. Kernel crash dumps can be used to debug kernel panics and other issues that cause the kernel to crash.

Kernel crash dumps can be generated in several ways, including using the syslogd daemon, the kdump utility, or the netconsole kernel module. These tools allow you to capture and save the crash dump to a file or send it over the network for further analysis.

Kernel crash dumps can be very useful for debugging and troubleshooting issues with the Linux kernel. They can provide valuable insights into what went wrong and help you identify the root cause of the issue. This is called Linux kernel crash dump analysis.

History Of Linux Kernel Crash Dump

The concept of kernel crash dumps has been around for a long time in the Unix world. In the early days of Unix, kernel crash dumps were typically saved to a device such as a serial port or network connection, and a separate machine was used to capture and analyze the crash dump.

In the Linux world, the kdump utility was introduced in 2005 as a way to capture and save kernel crash dumps to a file. The kdump utility is based on the kexec utility, which was developed by IBM to allow the Linux kernel to boot into a new kernel image without going through the full boot process.

In recent years, other tools such as the syslogd daemon and the netconsole kernel module have also been developed to allow for the logging and analysis of kernel crash dumps in Linux. These tools have made it easier for developers and system administrators to debug and troubleshoot issues with the Linux kernel.

Different Methods Of Logging Linux Kernel Crash Dump

There are several ways to log crash dumps in Linux. Let us discuss about all these three important methods how to enable the crash dump, disable the crash dump, or change as per the user requirement in the kernel.

1. Linux Kernel Crash Dump Using “syslogd daemon“

To capture kernel crash dumps on a Linux system, you can use the “syslogd” daemon to save the crash information to a log file. This is useful for debugging kernel panics and other issues that cause the system to crash.

Configuration Of Linux Kernel Crash Dump Using “syslogd daemon“

To enable kernel crash dumps with syslogd, you will need to modify the syslogd configuration file to specify where the crash dumps should be saved. This is typically done by adding a “kmsg” entry to the syslogd configuration file, which specifies the path to the log file where the crash dumps should be saved.

It can be configured to log kernel crash messages by adding the following line to the file:

'/etc/syslog.conf'

The crash log will be stored in the below file if you will not change or configure anything after enable.

kern.* /var/log/kern.log

After making this change, you will need to restart the syslogd daemon for the changes to take effect. You can do this by running sudo service syslogd restart.

Suppose, you want to save kernel crash dumps to a file called “crash.log” in the “/var/log” directory, you would add the following line to the syslogd configuration file:

kmsg -/var/log/crash.log

Once you have made this change, you will need to restart the syslogd daemon to apply the changes. You can do this by running the following command:

sudo service syslogd restart

Now, whenever the kernel crashes, the crash information will be saved to the “crash.log” file in the “/var/log” directory. You can then use this information to troubleshoot the issue and identify the cause of the kernel panic.

2. Linux Kernel Crash Dump Using “kdump utility“

The “kdump” utility is a tool for capturing kernel crash dumps on a Linux system. It is typically used to capture kernel crash dumps when the primary kernel (also known as the “running kernel“) crashes and is unable to save the crash information itself.

Configuration Of Linux Kernel Crash Dump Using “kdump utility“

To configure the “kdump” utility, you will need to edit the configuration file located at “/etc/kdump.conf“. This file contains various options that control the behavior of the “kdump” utility, such as where the crash dumps should be saved, and how much memory should be reserved for the crash dump kernel.

Here are some of the main options that you can configure in the “/etc/kdump.conf” file:

• “path” – This option specifies the location where the crash dumps should be saved. The default location is “/var/crash“.
• “core_collector” – This option specifies the program that should be used to collect the crash dump. The default value is “makedumpfile”.
• “extra_bins” – This option specifies a list of additional binary files that should be included in the crash dump. This can be useful for debugging issues that involve specific binaries or libraries.
• “extra_modules” – This option specifies a list of additional kernel modules that should be included in the crash dump. This can be useful for debugging issues that involve specific kernel modules.

Example For Configuration Of Linux Kernel Crash Dump Using “kdump utility“

Here is an example of how you might configure the “kdump” utility to capture kernel crash dumps on a Linux system:

1. Edit the “/etc/kdump.conf” file and set the “path” option to specify the location where the crash dumps should be saved. For example:

path /var/crash

This will save the crash dumps to the “/var/crash” directory.

2. Set the “core_collector” option to specify the program that should be used to collect the crash dump. For example:

core_collector makedumpfile

This will use the “makedumpfile” program to collect the crash dump.

3. Optionally, set the “extra_bins” and “extra_modules” options to specify additional binary files and kernel modules that should be included in the crash dump. For example:

extra_bins /usr/bin/foo /usr/bin/bar 
extra_modules foo.ko bar.ko

This will include the binary files “/usr/bin/foo” and “/usr/bin/bar“, as well as the kernel modules “foo.ko” and “bar.ko“, in the crash dump.

4. Save the “/etc/kdump.conf” file and start the “kdump” service:

sudo kdumpctl start

5. If the kernel crashes, the “kdump” utility will capture the crash information and save it to the location specified in the “/etc/kdump.conf” file. You can then use this information to troubleshoot the issue and identify the cause of the kernel panic

Once you have modified the “/etc/kdump.conf” file to specify the desired options, you can use the “kdumpctl” utility to start the “kdump” service. For example, you can use the following command to start the “kdump” service:

sudo kdumpctl start

Now, whenever the primary kernel crashes, the “kdump” utility will capture the crash information and save it to the location specified in the “/etc/kdump.conf” file. You can then use this information to troubleshoot the issue and identify the cause of the kernel panic.

There are many other options and configurations that you can use, depending on your specific needs.

3. Linux Kernel Crash Dump Using “netconsole kernel module“

The “netconsole” kernel module is another tool that can be used to capture kernel crash dumps on a Linux system. It works by sending the crash information over the network to a remote host, which can then save the information to a log file for later analysis.

Configuration Of Linux Kernel Crash Dump Using “netconsole kernel module“

To Configure or use the “netconsole” kernel module, you will need to load the module into the kernel and configure it to send the crash information to the desired destination. This is typically done by adding the following lines to the kernel command line in the boot loader configuration file:

netconsole=@/<local-ip>/<remote-ip>,<local-port>/<remote-port>

Here are the meanings of the various parameters:

• “local-ip” is the IP address of the network interface on the local host that will be used to send the crash information.
• “remote-ip” is the IP address of the network interface on the remote host that will receive the crash information.
• “local-port” is the port number on the local host that will be used to send the crash information.
• “remote-port” is the port number on the remote host that will receive the crash information.

Example Configuration Of “netconsole kernel module“

Here is an example of how you might configure the “netconsole” kernel module to capture kernel crash dumps on a Linux system:

• Edit the boot loader configuration file (e.g. “/etc/grub.conf” or “/boot/grub/grub.cfg“) and add the following lines to the kernel command line:

netconsole=@192.168.1.10/192.168.1.20,6666/6666

This tells the “netconsole” kernel module to send the crash information to the IP address “192.168.1.20” on port “6666“, using the network interface with IP address “192.168.1.10” on the local host.

• Save the boot loader configuration file and reboot the system.
• On the remote host, start a netcat session to listen for incoming crash information:

nc -l -u -p 6666 > crash.log

This will start a netcat session that listens for incoming traffic on port “6666” and saves the data to a file called “crash.log“.

• Once you have added these lines to the kernel command line, you will need to boot the system and load the “netconsole” kernel module. On the local host, load the “netconsole” kernel module:

sudo modprobe netconsole

If the kernel crashes, the “netconsole” kernel module will send the crash information over the network to the remote host, where it will be saved to the “crash.log” file. You can then use this information to troubleshoot the issue and identify the cause of the kernel panic.

Please remember that this is just one way to configure the “netconsole” kernel module. There are many other options and configurations that you can use, depending on your specific needs. If still you are having any doubt, you can use our Piest Forum Platform to ask your queries to get the best solution.

Advantages and Disadvantages Of Linux Kernel Crash Dump

There are lot of merits that forces the engineer to know and learn for real time bug analysis and fix it.

I hope this will help you in learning of Linux Kernel Crash Dump logging and using it in your company project work.