  Let $\Gamma_{k}(V)$ be the Grassmann graph formed by $k$-dimensional
subspaces of an $n$-dimensional vector space over the finite field ${\mathbb
F}_{q}$ consisting of $q$ elements and $1<k<n-1$. Denote by $\Gamma(n,k)_q$ the
restriction of the Grassmann graph to the set of all non-degenerate linear
$[n,k]_q$ codes. We describe maximal cliques of the graph $\Gamma(n,k)_q$ and
show that every automorphism of this graph is induced by a monomial semilinear
automorphism of $V$.
