More on this later in this article. The grub. 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. 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.
If you have access to a grub. The main set of configuration files for grub. Each of the files in that directory contains GRUB code that is collected into the final grub.
The numbering scheme used in the names of these configuration files is designed to provide ordering so that the final grub. 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.
The delimiting comments look like this:. These files should not be modified unless you are a GRUB expert and understand what the changes will do. Even then you should always keep a backup copy of the original, working grub. You should still be aware of the consequences of any changes you make to these files and maintain a backup of the original grub.
One reason for doing that might be to add a menu line for a non-Linux operating system. Configuration of the original GRUB was fairly simple and straightforward. In addition, grub. However, the GNU. Changing the configuration for GRUB2 is fairly easy once you actually figure out how to do it. I only discovered this while researching GRUB2 for a previous article.
You can simply change the values of existing keys or add other keys that are not already in the file. Section 5. I have never had needed to do anything other than modifying the values of some of the keys that are already in the grub default file. The Esc key discards any changes and reloads the standard menu interface. The c key loads the command line interface. The command line interface is the most basic GRUB 2 interface, but it is also the one that grants the most control.
The command line makes it possible to type any relevant GRUB 2 commands followed by the Enter key to execute them. In addition, the arrow , Home , End , and Delete keys work as they do in the bash shell.
Rescue mode provides a convenient single-user environment and allows you to repair your system in situations when it is unable to complete a normal booting process. In rescue mode, the system attempts to mount all local file systems and start some important system services, but it does not activate network interfaces or allow more users to be logged into the system at the same time.
In Red Hat Enterprise Linux 7, rescue mode is equivalent to single user mode and requires the root password. Note that equivalent parameters, 1 , s , and single , can be passed to the kernel as well. Emergency mode provides the most minimal environment possible and allows you to repair your system even in situations when the system is unable to enter rescue mode. In emergency mode, the system mounts the root file system only for reading, does not attempt to mount any other local file systems, does not activate network interfaces, and only starts few essential services.
In Red Hat Enterprise Linux 7, emergency mode requires the root password. Note that equivalent parameters, emergency and -b , can be passed to the kernel as well.
The systemd debug shell provides a shell very early in the startup process that can be used to diagnose systemd related boot-up problems. Once in the debug shell, systemctl commands such as systemctl list-jobs , and systemctl list-units can be used to look for the cause of boot problems.
In addition, the debug option can be added to the kernel command line to increase the number of log messages. For systemd , the kernel command-line option debug is now a shortcut for systemd. If required, the debug shell can be set to start on every boot by enabling it with the systemctl enable debug-shell command.
Alternatively, the grubby tool can be used to make persistent changes to the kernel command line in the GRUB 2 menu. See Section Permanently enabling the debug shell is a security risk because no authentication is required to use it.
Disable it when the debugging session has ended. During the boot process, the systemd-debug-generator will configure the debug shell on TTY9. If required, to verify you are in the debug shell, enter a command as follows:. To diagnose start up problems, certain systemd units can be masked by adding systemd.
To start additional processes during the boot process, add systemd. The systemd-debug-generator 8 manual page describes these options. Setting up the root password is a mandatory part of the Red Hat Enterprise Linux 7 installation.
If you forget or lose the root password it is possible to reset it, however users who are members of the wheel group can change the root password as follows:. The root password is now required to operate in single-user mode as well as in emergency mode. Two procedures for resetting the root password are shown here:. Remove the autorelable file to prevent a time consuming SELinux relabel of the disk:.
Remove the rhgb and quiet parameters from the end, or near the end, of the linux16 line, or linuxefi on UEFI systems. The rhgb and quiet parameters must be removed in order to enable system messages.
The initramfs will stop before passing control to the Linux kernel , enabling you to work with the root file system. Note that the initramfs prompt will appear on the last console specified on the Linux line.
With an encrypted file system, a password is required at this point. However the password prompt might not appear as it is obscured by logging messages. You can press the Backspace key to see the prompt. Release the key and enter the password for the encrypted file system, while ignoring the logging messages.
You will not be allowed to change the password if the file system is not writable. Enter the passwd command and follow the instructions displayed on the command line to change the root password. Note that if the system is not writable, the passwd tool fails with the following error:. Updating the password file results in a file with the incorrect SELinux security context.
To relabel all files on next system boot, enter the following command:. Enter the exit command again to resume the initialization and finish the system boot. With an encrypted file system, a pass word or phrase is required at this point. You can press and hold the Backspace key to see the prompt. Note that the SELinux relabeling process can take a long time. A system reboot will occur automatically when the process is complete. Enter the following commands to turn SELinux policy enforcement back on and verify that it is on:.
The Unified Extensible Firmware Interface UEFI Secure Boot technology ensures that the system firmware checks whether the system boot loader is signed with a cryptographic key authorized by a database of public keys contained in the firmware.
With signature verification in the next-stage boot loader and kernel, it is possible to prevent the execution of kernel space code which has not been signed by a trusted key. A chain of trust is established from the firmware to the signed drivers and kernel modules as follows. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. In what disk is GRUB located? Ask Question. Asked 8 years, 1 month ago.
Active 8 years, 1 month ago. Viewed 2k times. So long story short in what disk are GRUB files located? Improve this question. When it is not which would be really strange , then you could technically retain the grub. If you run mount and see something like this:. You have Grub2 installed in its own partition, as it should be. Normally, when installing a new distro, the wizzard will usually guide you through the installation process, and even figure out what partitions contain what OS-es, if applicable.
The process on Arch is a bit more tedious but very well documented. At this point I'm not sure if partitions need to be all mounted for Grub2 to detect the OS-es on them, though.
If you tried to install Windows in the mean time, it might be Windows overwrote the boot loader. To fix that, simply run as root or with sudo :. Grub2 is a Stage-2 boot loader. Meaning it's not exactly an operating system, but it's much more complex, than a simple chainloader, which would fit into the first bytes on your primary partition the rest of the first sector is partition table, flags, etc. Grub2 then either chainloads into another partition for booting windows for instance, as it installs its own boot loader , but it can also run code things like memtest , or access and run a kernel and module image vmlinuz.
What's important to note, is that in both instances Grub2 is unloaded from memory once a kernel starts running, or another partition has been chainloaded. Grub is not tied to a particular OS. It can reside on its private partition, though usually it's installed along the main file system. But for it to be able to boot your system s , it needs to know about them.
So you need to update Grub after any important changes in the systems present on your machine like a new OS installed or a kernel upgrade. If you delete the only Grub there is, you will not boot your system s.
There can be many Grubs on one machine, but only one is main, or active. Apart from Grub, there are other boot loaders that can be used instead of Grub.
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