  The generalized Chaplygin gas cosmology provides a prime example for the
class of unified dark matter models, which substitute the two dark components
of the standard cosmological LCDM concordance model by a single dark component.
The equation of state of the generalized Chaplygin gas is characterised by a
parameter alpha such that the standard LCDM model is recovered in the case
alpha=0 with respect to the background dynamics and the cosmic microwave
background (CMB) statistics. This allows to investigate the concordance of
different cosmological data sets with respect to alpha. We compare the
supernova data of the Supernova Cosmology Project, the data of the baryon
oscillation spectroscopic survey (BOSS) of the third Sloan digital sky survey
(SDSS-III) and the CMB data of the Planck 2015 data release. The importance of
the BOSS Lyman alpha forest BAO measurements is investigated. It is found that
these data sets possess a common overlap of the confidence domains only for
Chaplygin gas cosmologies very close to the LCDM model.
