  The Cauchy problem for the parabolic--elliptic Keller--Segel system in the
whole $n$-dimensional space is studied. For this model, every constant $A \in
\mathbb{R}$ is a stationary solution. The main goal of this work is to show
that $A < 1$ is a stable steady state while $A > 1$ is unstable. Uniformly
local Lebesgue spaces are used in order to deal with solutions that do not
decay at spatial variable on the unbounded domain.
