Root password reset in Linux

  

   1. Select the kernel
   2. Press the "e" key to edit the entry
   3. Select second line (the line starting with the word kernel)
   4. Press the "e" key to edit kernel entry so that you can append single user mode
   5. Append the letter "S" (or word Single) to the end of the (kernel) line
   6. Press ENTER key
   7. Now press the b key to boot the Linux kernel into single user mode
   8. At prompt type passwd command to reset password:

You need to mount at least / and other partitions:
# mount -t proc proc /proc
# mount -o remount,rw /

Change the root password,

# passwd

thenreboot system:
# sync
# reboot