GNU Grub恢复模式密码操作失误致Ubuntu 22.04设备锁定，咨询默认密码问题

Hey there, let's sort this out for you first: there is no default Grub password whatsoever. Grub doesn't come with any pre-set password protection out of the box—this is exactly why you're locked out right now. You added configuration to force authentication on boot, but failed to set a valid encrypted password, so the system has no valid credentials to accept, leading to the lockout.

如何恢复正常访问你的Ubuntu系统 #

Follow these steps to fix the lockout using an Ubuntu 22.04 live USB/CD:

1. Boot your device from the Ubuntu live media, and select "Try Ubuntu" to enter the live desktop environment.
2. Identify your system's main partition: Open a terminal and run lsblk—look for the partition with the ext4 filesystem (usually something like /dev/sda2 or /dev/nvme0n1p2 depending on your disk type).
3. Mount your system partition:

   sudo mkdir /mnt/ubuntu
   sudo mount /dev/your-system-partition /mnt/ubuntu
   

   If you have a separate EFI partition (common on UEFI systems), mount it too:

   sudo mount /dev/your-efi-partition /mnt/ubuntu/boot/efi
   

4. Enter the chroot environment to access your local system:

   sudo chroot /mnt/ubuntu
   

5. Remove the faulty Grub password configuration:
   Open the custom Grub config file with a text editor:

   nano /etc/grub.d/40_custom
   

   Look for lines you added earlier related to Grub authentication (like set superusers="root" or password root ...). Delete these lines, or comment them out by adding a # at the start of each line. Save the file (press Ctrl+O, then Enter, then Ctrl+X to exit nano).
6. Update Grub to apply the changes:

   update-grub
   

7. Exit chroot and reboot:

   exit
   sudo reboot
   

   Remove the live media when prompted, and your system should boot normally again.

正确设置Grub恢复模式密码（避免再次出错） #

Once you're back in your system, here's the correct way to set a password for recovery mode only:

1. Generate an encrypted password for Grub:
   Run this command in the terminal, then follow the prompts to enter your desired password twice:

   grub-mkpasswd-pbkdf2
   

   Copy the long encrypted string that starts with grub.pbkdf2.sha512...—you'll need this next.
2. Edit the custom Grub config:

   sudo nano /etc/grub.d/40_custom
   

   Add these lines (replace your-username with your actual Ubuntu username, and paste the encrypted string you copied):

   set superusers="your-username"
   password_pbkdf2 your-username grub.pbkdf2.sha512.10000...[your-encrypted-string]
   

3. Update Grub to apply the correct configuration:

   sudo update-grub
   

   Now, when you boot into recovery mode, it will prompt for your username and the password you set, while normal boot will work without any prompts.

备注：内容来源于stack exchange，提问作者a noob