How to Harness the Power of Open Source – Welcome to the World of Ubuntu

How to Reset Your Forgotten Ubuntu Password

Basics of Ubuntu
佐川 直弘 | Naohiro Sagawa
By 佐川 直弘 | Naohiro Sagawa (運営者)
※記事内に広告を含みます。Amazonアソシエイトとして適格販売により収入を得ています。　
目次

1. Introduction

Forgetting your Ubuntu password is a common issue, and this article explains how to reset it. It’s important to note that using these methods without permission on someone else’s system is illegal—you should only apply them to your own system. Additionally, enhancing security after resetting your password is crucial.

2. Understanding Ubuntu’s Password System

To enhance security, Ubuntu disables the root account by default. Resetting a password requires physical access to the system and involves using recovery mode or single-user mode. After resetting, reviewing and strengthening your system’s security is highly recommended.

3. Method 1: Resetting Password Using the GRUB Bootloader

Steps:

  1. Access the GRUB menu: Restart your computer and hold down the Shift key to display the GRUB bootloader menu.
  2. Select Recovery Mode: Choose Ubuntu (recovery mode) from the menu and press e to edit the boot command line.
  3. Edit the Command Line: Locate the line starting with linux and replace ro with rw init=/bin/bash.
  4. Boot into the System: Press Ctrl + X or F10 to boot into the root shell prompt.
  5. Reset the Password: Type passwd <username> and enter a new password twice.
  6. Reboot the System: Execute the command exec /sbin/init to restart your system.

Caution:

  • Editing the GRUB menu can affect your system, so proceed carefully.
  • After resetting the password, verify and strengthen your system’s security as needed.

4. Method 2: Accessing Single-User Mode

Steps:

  1. Boot into Single-User Mode: In the GRUB menu, select (recovery mode) and then choose root Drop to root shell prompt.
  2. Change the Password: In the root shell, type passwd <username> and set a new password.
  3. Reboot: Use the reboot command to restart the system.

Limitations & Security Considerations:

  • Single-user mode is not available on all Ubuntu versions. Use it only when you have physical access to the machine and consider security measures after recovery.

5. Alternative Recovery Methods

Using a Live USB

It is possible to access your Ubuntu system and reset your password using a Live USB. Boot your system using a Live USB and modify the /etc/shadow file to reset the password. This method is useful if other recovery options are not available.

Ubuntu Recovery Console

Another option is using the Ubuntu recovery console to reset the password. However, this requires advanced system administration knowledge. Before attempting this method, ensure you have a backup of important data in case of critical system issues.

6. Preventative Measures for the Future

Regular Backups

To prevent unexpected data loss during password resets, regular backups are essential. Important data and configuration files should be backed up to external storage.

Using a Password Manager

Password managers like KeePass or LastPass can securely store strong passwords, reducing the risk of forgetting them while improving overall security.

Creating a Recovery Disk

Preemptively creating a Live USB can help you quickly recover your system when a password reset is needed.

7. Troubleshooting Common Issues

GRUB Menu Not Appearing

If the GRUB menu does not appear, try holding the Shift key while rebooting. In dual-boot environments, another OS may automatically load, so check your BIOS/UEFI settings and adjust the boot order if necessary.

Permission Denied Error

If the file system is mounted as read-only in recovery mode, use the command mount -o remount,rw / to remount it with write permissions.

System Issues After Password Reset

If the system does not function properly after resetting the password, check the system logs to identify any issues. Pay special attention to security-related error messages, as they may indicate misconfigured settings.

8. Conclusion

If you forget your Ubuntu password, you can reset it using the GRUB bootloader or single-user mode. However, these methods come with security risks, so proceed carefully and review your system’s security settings after recovery. Regular backups and password management tools can help minimize risks and prevent future password-related issues.

9. FAQ

Q1: What security measures should I take after a password reset?

A1: After resetting your password, consider setting a strong password, enabling a firewall, disabling unnecessary services, and implementing two-factor authentication. Keeping your system’s software up to date is also essential.

Q2: What should I do if my system won’t boot after a password reset?

A2: If your system fails to boot after resetting the password, restart it in recovery mode via the GRUB menu and check the system logs (e.g., /var/log/syslog) for error messages. If necessary, consult a professional for assistance.

Q3: What if none of the password reset methods work?

A3: If you cannot reset your password using any of the described methods, try booting from a Live USB. This will allow you to back up your data before reinstalling Ubuntu. Some installation options allow you to retain your files, but having a backup is always recommended.

Q4: My system became unstable after a password reset. What should I do?

A4: If your system is unstable, perform a system update, check the file system for errors, and review system logs. If issues persist, consider adjusting your configuration settings or reinstalling Ubuntu.