1.8. Dumping the Crashed Kernel Using the kdump Mechanism

This section provides an introduction to the Kernel crash dump mechanism, also called kdump, and briefly explains what kdump is used for in Section 1.8.1, “What kdump Is and Which Tasks It Can Be Used For”.
Activation of the kdump service is a part of the installation process, and by default, kdump was enabled during the installation. This section summarizes how to activate kdump during the installation in Section 1.8.2, “Enabling and Activating kdump During the Installation Process”, and how to manually enable the kdump service if it is disabled after the installation in Section 1.8.3, “Ensuring That kdump Is Installed and Enabled after the Installation Process”.
You can also use Cockpit to configure kdump. See Section 1.8.4, “Configuring kdump in Cockpit” for more information.

1.8.1. What kdump Is and Which Tasks It Can Be Used For

In case of a system crash, you can use the Kernel crash dump mechanism called kdump that enables you to save the content of the system's memory for later analysis. The kdump mechanism relies on the kexec system call, which can be used to boot a Linux kernel from the context of another kernel, bypass BIOS, and preserve the contents of the first kernel's memory that would otherwise be lost.
When kernel crash occurs, kdump uses kexec to boot into a second kernel (a capture kernel), which resides in a reserved part of the system memory that is inaccessible to the first kernel. The second kernel captures the contents of the crashed kernel's memory (a crash dump) and saves it.

1.8.2. Enabling and Activating kdump During the Installation Process

During the installation, enablement and activation of kdump can be done either in the Anaconda installer or using the %addon com_redhat_kdump command in the Kickstart file.
For more information, see the appropriate source according to the installation method:

1.8.3. Ensuring That kdump Is Installed and Enabled after the Installation Process

To ensure that kdump is installed and to configure it:

Procedure 1.5. Checking Whether kdump Is Installed and Configuring kdump

  1. To check whether kdump is installed on your system:
    ~]$ rpm -q kexec-tools
  2. If not installed, to install kdump, enter as the root user:
    ~]# yum install kexec-tools
  3. To configure kdump:
    Use either the command line or graphical user interface.
    Both options are described in detail in Red Hat Enterprise Linux 7 Kernel Crash Dump Guide.
    If you need to install the graphical configuration tool:
    ~]# yum install system-config-kdump

1.8.4. Configuring kdump in Cockpit

In Cockpit, select Kernel dump configuration to verify:
  • the kdump status
  • the amount of memory reserved for kdump
  • the location of the crash dump files
Configuring kdump in Cockpit

Figure 1.5. Configuring kdump in Cockpit

1.8.5. Additional Resources on kdump

For more information on kdump, see Red Hat Enterprise Linux 7 Kernel Crash Dump Guide.