Imagine this scenario: you’re managing a remote server that suddenly becomes unresponsive. You can’t log in via SSH, websites aren’t working, and pings are either delayed or timing out. All you have left is a “hard” reboot through your hosting provider’s panel, risking data loss and filesystem corruption.
But what if there was a way to “talk” to the kernel even when the rest of the system is down? This last resort is the Magic SysRq key.
dmesg?dmesg (short for “display message” or “driver message”) is one of the most important and simplest diagnostic tools in any Linux system. It allows you to read messages from the kernel ring buffer.
Think of this buffer as your system’s black box. From the very moment the computer starts, the Linux kernel writes all important information into it: what it has detected, which drivers it has loaded, and whether it has encountered any errors. dmesg is the command that lets us look inside this box.
Most Linux users use pre-built kernels provided by their distribution. This is convenient and perfectly sufficient. However, compiling your own kernel opens up a world of new possibilities and is a fundamental skill for anyone who wants to deeply understand how the system works.
The main reasons to do it are:
This guide will walk you through the entire process, step by step.
In the previous article, we discussed how to configure the system to automatically reboot after a Kernel Panic using the kernel.panic parameter. But what if we want to understand why the panic occurred? Simply restarting the system solves the availability problem but doesn’t help diagnose the cause. This is where kdump comes in.
kdump is an advanced mechanism in the Linux kernel that allows capturing the contents of system memory (a memory dump or crash dump) at the moment a Kernel Panic occurs. This dump can then be analyzed using specialized tools, such as crash, to identify a faulty driver, a bug in the kernel code, or another cause of the failure.
A Kernel Panic is one of the most serious errors that can occur in a Linux operating system. It’s a situation where the system’s kernel encounters a critical error from which it cannot recover. As a result, the system halts its operations to prevent further data corruption. Typically, a detailed error message is displayed on the screen, and the system becomes unresponsive.
Although a Kernel Panic may look intimidating, it is a defense mechanism. But what should the system do after a panic occurs? This is where the kernel.panic parameter comes in.
make oldconfig?When you’re building the Linux kernel, one of the most important steps is configuring it. The kernel has thousands of options that can be enabled or disabled, and manually going through all of them would be incredibly time-consuming. This is where make oldconfig comes in.
The make oldconfig command is one of several configuration tools that come with the kernel source. Its main purpose is to update an existing configuration file (.config) with respect to new options available in a newer kernel version.
vmlinuz file?If you’ve ever looked into your Linux system’s /boot directory, you’ve surely come across a file with the mysterious name vmlinuz (or vmlinuz-6.5.0-generic, etc.). This is one of the most important files in the entire system – it’s the compressed, bootable image of the Linux kernel.
In short, this is the file that is loaded into memory by the bootloader (like GRUB) when the computer starts. Once loaded, a small piece of code inside vmlinuz decompresses the rest of the kernel into RAM and then transfers control to it, beginning the actual startup process of the operating system.