Be aware that the memory reserved for the kdump kernel at boot time cannot be used by the standard kernel, which changes the actual minimum memory requirements of Red Hat Enterprise Linux. The first kernel reserves a section of memory that the second kernel uses to boot. This second kernel, often called a capture kernel, boots with very little memory and captures the dump image. Kdump uses kexec to boot into a second kernel whenever the system crashes. The crash dumps are captured from the context of a freshly booted kernel not from the context of the crashed kernel. Kdump is a reliable kernel crash-dumping mechanism that utilizes the kexec software. Using kexec for rebooting into a normal kernel is simple, but not within the scope of this article. Since BIOS checks at startup can be very time consuming (especially on big servers with numerous peripherals), kexec can save a lot of time for developers who need to reboot a machine often for testing purposes. Kexec is a fastboot mechanism that allows to boot a Linux kernel from the context of an already running kernel without going through the BIOS.
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