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6.2. Changing GRUB entries at boot

Changing selection or adding arguments to a GRUB menu entry at boot time can be useful for testing or troubleshooting purposes. You might have a graphics issue to troubleshoot by booting temporarily into a non-graphical target, a hardware issue to work around with a kernel parameter, or a problem to resolve by selecting an alternate kernel. This section covers the procedure for adding boot arguments, see Section 9, “Boot Options” for some arguments you might use.

The Rescue option

The normal boot entries for Fedora use a trimmed down initramfs, or initial boot filesystem. This host-only initramfs had information only about the hardware on your computer, allowing the system to boot more quickly by avoid loading unneeded drivers.
One of the default menu entries for Fedora is a rescue entry. This will load the same Fedora environment as the other entries, but loads a full initramfs.
The rescue option is useful if you have problems after adding new hardware. You can use the rescue option to regenerate the initramfs for all boot entries using this command:
# dracut --regenerate-all --force
  1. Turn on or reboot your computer. When the GRUB menu ( Figure 1, “GRUB menu during countdown” ) appears, press the Esc key to stop the countdown.
    GRUB menu during countdown
    The GRUB menu is a text based interface with a list of bootable systems. The entries for Fedora include the kernels available to boot and the rescue option. The menu counts down from a defined value, 5 seconds by default, before booting the default entry.
    Figure 1. GRUB menu during countdown

  2. Use the arrow keys to highlight the desired boot entry.
    1. If you want to boot an alternate menu entry without editing, press Enter to continue.
    2. If you want to edit the entry before booting, press e to edit.
    1. The initial screen displayed for editing shows information GRUB needs to find and boot the operating system, as pictured in Figure 2, “The GRUB edit screen, Part 1”. These lines should not be changed.
      The GRUB edit screen, Part 1
      The initial edit screen shows several lines of parameters and modules that GRUB uses to boot the operating system.
      Figure 2. The GRUB edit screen, Part 1

    2. Using the arrow keys, move down to the line that contains the boot arguments. On UEFI systems, this line will begin with linuxefi, or on BIOS systems the line will begin with linux. The next argument on the line will typically be the kernel, a string beginning with /vmlinuz-. This is shown in Figure 3, “The GRUB edit screen, Part 1”.
      Press the End key to move to the end of the line.
      The GRUB edit screen, Part 1
      Scrolling down reveals the line with boot arguments.
      Figure 3. The GRUB edit screen, Part 1

      Getting more information during boot

      The default boot parameters for Fedora include rghb and quiet. These enable the boot splash screen instead of showing details about services, mountpoints, and other units as the sytem boots. If you are troubleshooting a boot issue or want to see more information when Fedora loads, removing these parameters will disable the splash screen.
  3. Type in your desired parameters and press Ctrl+x to boot. See Section 9, “Boot Options” for some parameters you might find useful.