There are people frequently asked such question: How should we go about finding a root teacher? Here is the answers from Gyalwai Nyugu Rinpoche:

It is important to understand peoples arising causes and merit. There are many different types of teachers. We have teachers for worldly matters, meditation teachers and Bodhisattva teachers who are of great help to others but have not yet attained Buddhahood, and we have teachers who have attained perfect Buddhahood. There are many teachers in worldly matters. We may not yet have the merit to find teachers who are Buddhas. For this, sufficient merit is required.  Now there are two Karmapas and many people say this one is true, this one is false. Whether this is right or not I cannot answer myself. One would have to first fully observe them to be able to make this kind of judgement. There may even be highly realised teachers who are prostitutes or animals.

The best suggested way to go about finding a root teacher may be based on the root Lama’s practice. Ask yourself whether your root Lama embody’s the teachings? Look at your root Lama’s lineage, his compassion and loving kindness.

There are many teachers included in both the Hinayana, Mahayana and Vajrayana schools and we place huge requirements on them, even though we are in fact not so great ourselves. It is not necessary that they are true Buddhas, but that they may have great compassion, true wisdom and be from a virtuous lineage.

We may even meet the perfect root Lama, but due to our own situation, habits or afflictions, we may be unable to follow. Like a beggar that suddenly receives ten million dollars, and then blows all the money because he does not know what to do with it or how to invest the money wisely. Slowly, over time, the student will start to realise how good a teacher the root lama really is. Who you meet will maybe not be your enlightened teacher. To meet an enlightened teacher or a teacher who can teach the precepts is very special.

You will feel and know when you meet you root lama. Some people may compare it to meeting their ideal partner. In our heart, we may sometimes feel that we just know, but this is not the same. These may be accumultion of all forms of different feelings. When you meet your root lama you will feel a great tranquility, in your heart you will know, I am their student. Jigme Lingpa just heard the name of Longchenpa and knew that Longchenpa was his root master.