Sometimes it may happen with you that you forget your password and now you do not know how to login in your system so here is a trick,by this you can easily get and set your password again---
- Turn your computer on.Press ESC at the grub prompt.
- Press e for edit.
- Highlight the line that begins kernel ………, press e.
- Go to the very end of the line, add rw init=/bin/bash
- press enter, then press b to boot your system.
- Your system will boot up to a passwordless root shell.
- Type in passwd username.
- Set your password.
- Type in reboot.