The GRUB menu also provides a "rescue" kernel, in for use when troubleshooting or when the regular kernels don't complete the boot process for some reason. Pressing the Enter key immediately continues the boot process with either the default kernel or an optionally selected one. Pressing any key on the keyboard except the Enter key terminates the countdown timer which is displayed on the console. The GRUB menu also provides a timeout so that, if the user does not make any other selection, GRUB will continue to boot with the default kernel without user intervention. Using the up and down arrow keys allows you to select the desired kernel and pressing the Enter key continues the boot process using the selected kernel. The function of the GRUB menu is to allow the user to select one of the installed kernels to boot in the case where the default kernel is not the desired one. This has come in handy on a couple occasions when I had to revert to a kernel that was several versions down-level. I usually change the installonly_limit value to 9 to retain a total of nine kernels. The number of kernels to be kept before the package manager erases them is configurable in the /etc/dnf/dnf.conf or /etc/yum.conf files. By default, three kernels are kept–the newest and two previous–when yum or dnf are used to perform upgrades. Many times, booting to an older kernel can circumvent issues such as these.
I have found this to be a very useful tool because there have been many instances that I have encountered problems with an application or system service that fails with a particular kernel version. GRUB supports multiple Linux kernels and allows the user to select between them at boot time using a menu. Once the kernel takes over, GRUB has done its job and it is no longer needed. Its function is to take over from BIOS at boot time, load itself, load the Linux kernel into memory, and then turn over execution to the kernel. GRUB stands for GRand Unified Bootloader. This article provides a quick introduction to configuring GRUB2, which I will mostly refer to as GRUB for simplicity. When researching my article from last month, An introduction to the Linux boot and startup process, I became interested in learning more about GRUB2. Running Kubernetes on your Raspberry Pi.A practical guide to home automation using open source tools.6 open source tools for staying organized.An introduction to programming with Bash.A guide to building a video game with Python.