Portrait of Sadhu Baba. Varanasi,India. The Sanskrit terms sādhu ("good man") and sādhvī ("good woman") refer to renouncers who have chosen to live lives apart from or on the edges of society to focus on their own spiritual practices.
Becoming a sadhu is a path followed by millions. It is supposed to be the fourth phase in a Hindu's life, after studies, being a father and a pilgrim, but for most it is not a practical option. For a person to become sadhu needs vairagya. Vairagya means desire to achieve something by leaving the world (cutting familial, societal and earthly attachments).
A person who wants to become sadhu must first seek a guru. There, he or she must perform guruseva which means service. The guru decides whether the person is eligible to take sannyasa by observing the sisya (the person who wants to become a sadhu or sanyasi). If the person is eligible, guru upadesa (which means teachings)