I think I'm missing something about torques. Do supports exert torques? Consider these two situations I'm confused about.
A rod is attached in to a wall so that it cannot rotate. Since weight exerts a torque, the wall must do it too. But my doubt is: if I take A as point to measure torque, then it is necessarily zero and $\sum M =mg \frac{l}{2}\neq 0$. Nevertheless there is static equilibrium, how can that be?
Another situation is the one with a rod that can rotate about a point B, with another support in point C. Suppose there is also a weight on the rod in a particular position. Taking point B to measure torques, does the support in C exerts torque? In some exercises I noticed that the torque of the support in C is not considered for equilibrium. Furthermore, suppose to take a point to measure torque that differs from B, then does B exert torque?