Secara baku, kunci untuk direktif GRUB_DEFAULT di berkas /etc/default/grub adalah kata saved. Ini menginstruksikan GRUB 2 untuk memuat kernel yang ditentukan oleh direktif saved_entry dalam berkas lingkungan GRUB 2, yang terletak di /boot/grub2/grubenv. Anda dapat mengatur catatan GRUB lain menjadi baku, menggunakan perintah grub2-set-baku, yang akan memperbarui berkas lingkungan GRUB 2.

By default, the saved_entry value is set to the name of latest installed kernel of package type kernel. This is defined in /etc/sysconfig/kernel by the UPDATEDEFAULT and DEFAULTKERNEL directives. The file can be viewed by the root user as follows:

Direktif DEFAULTKERNEL menentukan jenis paket apa yang akan digunakan sebagai baku. Memasang paket tipe kernel-debug tidak akan mengubah kernel baku saat DEFAULTKERNEL diatur ke tipe paket kernel.

GRUB 2 mendukung penggunaan nilai numerik sebagai kunci untuk direktif saved_entry untuk mengubah urutan baku di mana sistem operasi dimuat. Untuk menentukan sistem operasi mana yang harus dimuat terlebih dahulu, berikan nomornya ke perintah grub2-set-default. Misalnya:

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 force a system to always use a particular menu entry, use the menu entry name as the key to the GRUB_DEFAULT directive in the /etc/default/grub file. To list the available menu entries, run the following command as root:

The file name /etc/grub2.cfg is a symlink to the grub.cfg file, whose location is architecture dependent. For reliability reasons, the symlink 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.

Changes to /etc/default/grub require rebuilding the grub.cfg file as follows:

If required to prepare a new GRUB 2 file with different parameters, edit the values of the GRUB_CMDLINE_LINUX key in the /etc/default/grub file. Note that you can specify multiple parameters for the GRUB_CMDLINE_LINUX key. For example:

Where console=tty0 is the first virtual terminal and console=ttyS0 is the serial terminal to be used.

Changes to /etc/default/grub require rebuilding the grub.cfg file as follows:

When executing the grub2-mkconfig command, GRUB 2 searches for Linux kernels and other operating systems based on the files located in the /etc/grub.d/ directory. The /etc/grub.d/10_linux script searches for installed Linux kernels on the same partition. The /etc/grub.d/30_os-prober script searches for other operating systems. Menu entries are also automatically added to the boot menu when updating the kernel.

The 40_custom file located in the /etc/grub.d/ directory is a template for custom entries and looks as follows:

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.

This is an example of a custom 40_custom script:

Alternatively, if you want to keep the files in the /etc/grub2.d/ directory, make them unexecutable by running the chmod a-x <file_name> command.

Dalam contoh di atas:

If you do not specify a user for a menu entry, or make use of the --unrestricted option, then only the superuser will have access to the system.

After you have made changes in the template file the GRUB 2 configuration file must be updated.

Rebuild the grub.cfg file by running the grub2-mkconfig -o command as follows:

By default, passwords are saved in plain text in GRUB 2 scripts. Although the files cannot be accessed on boot without the correct password, security can be improved by encrypting the password using the grub2-mkpasswd-pbkdf2 command. This command converts a desired password into a long hash, which is placed in the GRUB 2 scripts instead of the plain-text password.

The following format applies for the 01_users file:

The following format applies for the 40_custom file:

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 dnf reinstall grub2-efi shim 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 dnf reinstall grub2-efi shim command to reinstall GRUB 2 if the system is operating normally. For example:

This method completely removes all GRUB 2 configuration files and system settings. Apply this method to reset all configuration settings to their default values. Removing of the configuration files and subsequent reinstalling of GRUB 2 fixes failures caused by corrupted files and incorrect configuration. To do so, as root, follow these steps:

To set the system to use a serial terminal only during a single boot process, when the GRUB 2 boot menu appears, move the cursor to the kernel you want to start, and press the e key to edit the kernel parameters. Remove the rhgb and quit parameters and add console parameters at the end of the linux16 line as follows:

These settings are not persistent and apply only for a single boot.

To make persistent changes to a menu entry on a system, use the grubby tool. For example, to update the entry for the default kernel, enter a command as follows:

The --update-kernel parameter also accepts the keyword ALL or a comma separated list of kernel index numbers. See Adding and Removing Arguments from a GRUB Menu Entry for more information on using grubby.

If required to build a new GRUB 2 configuration file, add the following two lines in the /etc/default/grub file:

The first line disables the graphical terminal. Note that specifying the GRUB_TERMINAL key overrides values of GRUB_TERMINAL_INPUT and GRUB_TERMINAL_OUTPUT. On the second line, adjust the baud rate, parity, and other values to fit your environment and hardware. A much higher baud rate, for example 115200, is preferable for tasks such as following log files. Once you have completed the changes in the /etc/default/grub file, it is necessary to update the GRUB 2 configuration file.

Rebuild the grub.cfg file by running the grub2-mkconfig -o command as follows:

Alat screen berfungsi sebagai terminal serial yang mumpuni. Untuk memasangnya, jalankan sebagai root:

To connect to your machine using the serial console, use a command in the follow format:

By default, if no option is specified, screen uses the standard 9600 baud rate. To set a higher baud rate, enter:

Where console_port is ttyS0, or ttyUSB0, and so on.

To end the session in screen, press Ctrl+a, type :quit and press Enter.

See the screen(1) manual page for additional options and detailed information.

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 Fedora, rescue mode is equivalent to single user mode and requires the root password.

Tekan Ctrl+a dan Ctrl+e masing-masing untuk melompat ke awal dan akhir baris. Pada beberapa sistem, Home dan End mungkin juga berfungsi.

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 Fedora, emergency mode requires the root password.

Tekan Ctrl+a dan Ctrl+e masing-masing untuk melompat ke awal dan akhir baris. Pada beberapa sistem, Home dan End mungkin juga berfungsi.

Note that equivalent parameters, emergency and -b, can be passed to the kernel as well.

Setting up the root password is a mandatory part of the Fedora 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:

Note that in GRUB 2, resetting the password is no longer performed in single-user mode as it was in GRUB included in Fedora 15 and Red Hat Enterprise Linux 6. 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:

Tekan Ctrl+a dan Ctrl+e masing-masing untuk melompat ke awal dan akhir baris. Pada beberapa sistem, Home dan End mungkin juga berfungsi.

Adding the enforcing=0 option enables omitting the time consuming SELinux relabeling process.

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.

The initramfs switch_root prompt appears.

Remount the file system as writable:

Change the file system’s root as follows:

The prompt changes to sh-4.2#.

Note that if the system is not writable, the passwd tool fails with the following error:

Alternatively, to save the time it takes to relabel a large disk, you can omit this step provided you included the enforcing=0 option in step 3.

With an encrypted file system, a pass word or phrase is required at this point. However the password prompt might not appear as it is obscured by logging messages. You can press and hold the Backspace key to see the prompt. Release the key and enter the password for the encrypted file system, while ignoring the logging messages.

Enter the following commands to turn SELinux policy enforcement back on and verify that it is on:

Fedora includes support for the UEFI Secure Boot feature, which means that Fedora can be installed and run on systems where UEFI Secure Boot is enabled. On UEFI-based systems with the Secure Boot technology enabled, all drivers that are loaded must be signed with a valid certificate, otherwise the system will not accept them. All drivers provided by Red Hat are signed by the UEFI CA certificate.

If you want to load externally built drivers — drivers that are not provided on the Fedora Linux DVD — you must make sure these drivers are signed as well.