#Grub display menu code#

In addition, grub.cfg may be overwritten when a new kernel is installed, so any changes may disappear. cfg, but the new version is considerably more complex than the original GRUB. I could still modify GRUB2 by changing /boot/grub2/grub. I would just modify /boot/grub/nf and be good to go. GRUB defaults fileĬonfiguration of the original GRUB was fairly simple and straightforward.

Just be sure to follow the naming convention to ensure that the additional menu item is added either immediately before or after the 10_linux entry in the configuration file. One reason for doing that might be to add a menu line for a non-Linux operating system. You can also add your own files to the /etc/grub.d directory. You should still be aware of the consequences of any changes you make to these files and maintain a backup of the original grub. The specific files, 40_custom and 41_custom are intended to be used to generate user modifications to the GRUB configuration. Even then you should always keep a backup copy of the original, working grub. These files should not be modified unless you are a GRUB expert and understand what the changes will do. Each of these files has a comment to denote the beginning and end of the section, and those comments are also part of the final grub.cfg file so that it is possible to see from which file each section is generated. The numbering scheme used in the names of these configuration files is designed to provide ordering so that the final grub.cfg file is assembled into the correct sequence.

Each of the files in that directory contains GRUB code that is collected into the final grub.cfg file. The main set of configuration files for grub.cfg is located in the /etc/grub.d directory. The grub.cfg file is just too large to be included in this article. cfg file you should look at it to get a feel for what one looks like. For example, if you have four installed kernels, the most recent kernel will be at index 0, the previous kernel will be at index 1, and the oldest kernel will be index 3. The grub.cfg file contains Bash-like code and a list of installed kernels in an array ordered by sequence of installation. The / boot/grub2/ grub.cfg file is first generated during Linux installation and regenerated when a new kernel is installed. It is generated by the grub2-mkconfig program using a set of primary configuration files and the grub default file as a source for user configuration specifications. The grub.cfg file is the GRUB configuration file. Unfortunately, this rescue kernel does not boot to rescue mode. 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.

#Grub display menu code#