As the computer starts, GRUB 2 either presents a menu and awaits user input or automatically transfers control to an operating system kernel. It has been completely rewritten to provide the user significantly increased flexibility and performance. In this guide, GRUB 2 is version 1.
GRUB legacy version 0. To determine your version, use grub-install -V. Grub version 1. This guide covers the use of Grub 1. Content reflecting other versions of Grub 2 will be noted in the appropriate entry. On a new installation of Ubuntu 9. No menu will be displayed. In certain cases, pressing the ESC key may also display the menu.
Stage 1. It is the product of various scripts and should not normally be edited directly. The menu list of available Linux kernels is automatically generated by running update-grub.
It enables, for example, changing GRUB 2 menu entries to specify what arguments to pass to a kernel on system start and changing the default kernel. If that file cannot be found it will search for an architecture dependent default. To make a persistent change in the kernel designated as the default kernel, use the grubby command as follows:. On UEFI systems, all grubby commands must be entered as root. The --update-kernel option can be used to update a menu entry when used in combination with --args to add new arguments and --remove-arguments to remove existing arguments.
These options accept a quoted space-separated list. The command to simultaneously add and remove arguments a from GRUB 2 menu entry has the follow format:. This command removes the Red Hat graphical boot argument, enables boot message to be seen, and adds a serial console. As the console arguments will be added at the end of the line, the new console will take precedence over any other consoles configured. To review the changes, use the --info command option as follows:. To add the same kernel boot arguments to all the kernel menu entries, enter a command as follows:.
To change a value in an existing kernel argument, specify the argument again, changing the value as required. For example, to change the virtual console font size, use a command as follows:. To reflect the latest system boot options, the boot menu is rebuilt automatically when the kernel is updated or a new kernel is added.
However, users may want to build a menu containing specific entries or to have the entries in a specific order. GRUB 2 allows basic customization of the boot menu to give users control of what actually appears on the screen.
The following files are included:. With such setting, the system always boots immediately on the default menu entry, and if the default kernel fails to boot, it is not possible to boot an older kernel.
The file can be viewed by the root user as follows:. To specify which operating system should be loaded first, pass its number to the grub2-set-default command. For example:. Note that the position of a menu entry in the list is denoted by a number starting with zero; therefore, in the example above, the third entry will be loaded. This value will be overwritten by the name of the next kernel to be installed. To list the available menu entries, run the following command as root :. For reliability reasons, the symbolic link is not used in other examples in this chapter.
It is better to use absolute paths when writing to a file, especially when repairing a system. On BIOS-based machines, issue the following command as root :. On UEFI-based machines, issue the following command as root :. Menu entries are also automatically added to the boot menu when updating the kernel. This file can be edited or copied. Note that as a minimum, a valid menu entry must include at least the following:.
If you do not want menu entries to be updated automatically, you can create a custom menu. Rebuild the grub. Run the grub2-setpassword command as root:. With this change, modifying a boot entry during booting requires you to specify the root user name and your password.
Setting a password using the grub2-setpassword prevents menu entries from unauthorized modification but not from unauthorized booting. To also require password for booting an entry, follow these steps after setting the password with grub2-setpassword :. If you forget your GRUB 2 password, you will not be able to boot the entries you reconfigure in the following procedure. Delete the --unrestricted parameter from the menu entry block, for example:.
Now even booting the entry requires entering the root user name and password. Therefore, to retain password protection, use the above procedure after every use of grub2-mkconfig. The grub2-setpassword tool was added in Red Hat Enterprise Linux 7. Booting entries without the --unrestricted parameter requires the root password. However, GRUB 2 also enables creating additional non-root users that can boot such entries without providing a password. Modifying the entries still requires the root password.
Reinstalling GRUB 2 is a convenient way to fix certain problems usually caused by an incorrect installation of GRUB 2, missing files, or a broken system. Other reasons to reinstall GRUB 2 include the following:.
When using the grub2-install command, the boot information is updated and missing files are restored. Note that the files are restored only if they are not corrupted. Use the grub2-install device command to reinstall GRUB 2 if the system is operating normally.
For example, if sda is your device :. When using the yum reinstall grub2-efi shim command, the boot information is updated and missing files are restored. Use the yum reinstall grub2-efi shim command to reinstall GRUB 2 if the system is operating normally.
This method completely removes all GRUB 2 configuration files and system settings. GRUB 2 scripts search the user's computer and build a boot menu based on what operating systems the scripts find. To reflect the latest system boot options, the boot menu is rebuilt automatically when the kernel is updated or a new kernel is added.
However, users may want to build a menu containing specific entries or to have the entries in a specific order. Smart TVs Ads. Team Comes to Workplace by Meta. Block People Spotify. Verizon Selling PS5. Windows 11 SE Explained. Windows 11 SE. Microsoft Default Browser Firefox. Google's New Pet Art.
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