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What is kexec_load in RHEL – The Ranjan.info

February 8, 20244 min read

kexec_load Linux has a system call that loads a new kernel image into memory for execution, effectively allowing Linux systems to reboot rapidly without going through the full hardware initialization process. This system call is particularly useful in situations where the system crashes or when administrators need to load a different kernel without rebooting the entire system.

Understanding the specifics of the kexec/kdump interface in Red Hat Enterprise Linux (RHEL) is important for users who want to achieve optimal performance and reliability. While the default option is kexec_file_load, the availability of kexec_load provides users with flexibility, allowing them to customize their systems based on their specific needs. Red Hat maintains its commitment to supporting both interfaces, guaranteeing a seamless experience for users in a variety of use cases.

Here's how `kexec_load` works:

1. Loading a new kernel image: When invoked, `kexec_load` loads a new kernel image into memory. This kernel image can either be a different version of the currently running kernel or a completely different kernel.

2. Specifying kernel parameters: Along with the kernel image, `kexec_load` allows administrators to specify parameters for the new kernel. These parameters may include boot options, command-line arguments, and any other configuration settings required by the kernel.

3. Avoiding hardware initialization: Unlike a traditional system reboot, where the hardware goes through the full initialization process, `kexec_load` bypasses hardware initialization. This results in a faster reboot process as the system does not need to restart hardware components such as the CPU, memory and peripherals.

4. preservation of system state:kexec_load Preserves some aspects of the system state, such as the contents of memory and CPU state, before loading the new kernel image. This allows a seamless transition between the old and new kernels, minimizing downtime and disruption to running processes.

5. usage scenario:kexec_load is commonly used in scenarios where the system crashes and administrators need to immediately reboot the system using a known good kernel image. It can also be used for kernel testing, debugging, and performing system upgrades without requiring a complete system reboot.

As of Red Hat Enterprise Linux (RHEL) 8, the default interface for kexec/kdump to load the kernel is kexec_file_load. This significant change represents a strategic decision aimed at utilizing the capabilities of the kernel in this important process. Even though there has been a transition to using the kexec_file_load interface as the default method for loading the kexec/kdump kernel in Red Hat Enterprise Linux (RHEL) 8, it is important to note that the kexec_load interface remains available. This means that users still have the flexibility to use kexec_load if they have specific needs or preferences that require its use.

Overall, `kexec_load` provides a valuable mechanism for efficiently loading and executing kernel images in Linux systems, giving administrators greater flexibility and control over system reboots and kernel changes.

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