Root Password Recovery

• Root Password Recovery
  • GRUB
    • Ubuntu SOP
    • FreeBSD SOP
    • CentOS SOP
  • Reference
    • Official
    • Article

• One simple way is to let super-user uses privilege to change root's password.
• But if the super-user account cannot be accessed or there is no super-user, here is another way to fix the problem – GRUB.

GRUB

• Restart the system and hold the Shift key or press the Esc key to enter into safe mode (recovery mode). Once you have entered safe mode, you will see the GRUB menu.

Ubuntu SOP

1. Press Esc will enter BIOS, so you should press shift in order to see the option of recovery mode.
   
2. Get into root shell prompt without password, then you can change root's password.

FreeBSD SOP

1. Press shift then press shift-2 enter Boot Single user
   
2. The mount -a mentioned in article[2] doesn't work, should use the following one instead:
   ​mount -o rw -u /
   

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CentOS SOP

• The way to change boot mode at GRUB is different between CentOS7 and previous version.

1. Press e at default boot option
   
2. It will enter a text editor
   
3. Add rd.break at the end of the line which starts with Linux or kernel
   

   If the version of CentOS is lower than 7, the added string will be single

4. Press Ctrl-x to enter single-user mode
5. Remount the /sysroot/ and change root directory to /sysroot by following commands
   ​mount -o remount,rw /sysroot/
   ​chroot /sysroot
   

6. Change password
   
7. Reboot
   
   • Two ways
     • Faster
       ​​​load_policy -i
       ​​​chcon -t shadow_t /etc/shadow
       ​​​exit
       

     • Slower
       ​​​touch /.autorelabel
       ​​​exit
       

Reference

Official

Article

1. How to Reset or Change the Root Password in Ubuntu/CentOS
2. 如何重設 Ubuntu、CentOS、Debian、FreeBSD 的 root 密碼
3. Recover – Reset Forgotten Linux Root Password
4. CentOS 7 如何重置root密碼