Does a generalized Chaplygin gas correctly describe the cosmological
  dark sector?
  Yes, but only for a parameter value that makes it almost coincide with the
standard model. We reconsider the cosmological dynamics of a generalized
Chaplygin gas (gCg) which is split into a cold dark matter (CDM) part and a
dark energy (DE) component with constant equation of state. This model, which
implies a specific interaction between CDM and DE, has a $\Lambda$CDM limit and
provides the basis for studying deviations from the latter. Including matter
and radiation, we use the (modified) CLASS code \cite{class} to construct the
CMB and matter power spectra in order to search for a gCg-based concordance
model that is in agreement with the SNIa data from the JLA sample and with
recent Planck data. The results reveal that the gCg parameter $\alpha$ is
restricted to $|\alpha|\lesssim 0.05$, i.e., to values very close to the
$\Lambda$CDM limit $\alpha =0$. This excludes, in particular, models in which
DE decays linearly with the Hubble rate.
