7. For any positive numbers $a, b, c$ satisfying $a+b+c=1$, it always holds that
$$
\begin{array}{l}
a^{2}+b^{2}+c^{2}+\lambda \sqrt{a b c} \leqslant 1 . \\
\text { Then } \lambda_{\text {max }}=
\end{array}
$$