6. A. If the equation with respect to $x$
$$
(x-2)\left(x^{2}-4 x+m\right)=0
$$

has three roots, and these three roots can exactly serve as the three side lengths of a triangle, then the range of values for $m$ is
2,6. A. $30)$. Then $x_{1}+x_{2}=4, x_{1} x_{2}=m$.
From the given condition we know
$$
\begin{array}{l}
0 \leqslant x_{1}-x_{2}<2 \Rightarrow 0 \leqslant 16-4 m<4 \\
\Rightarrow 3<m \leqslant 4 .
\end{array}
$$