  Few independent detections of a weak X-ray line at an energy of $\sim$3.5 keV
seen toward a number of astrophysical sites have been reported. If this signal
will be confirmed to be the signature of decaying DM sterile neutrino with a
mass of ~7.1 keV, then the cosmological observables should be consistent with
its properties. In this paper we make a coupled treatment of the weak
decoupling, primordial nucleosynthesis and photon decoupling epochs in the
sterile neutrino resonant production scenario, including the extra radiation
energy density via N_eff. We compute the radiation and matter perturbations
including the full resonance sweep solution for active-sterile flavor
conversion in the expanding Universe. We show that the cosmological
measurements are in agreement with sub-dominant DM sterile neutrino resonant
production with following parameters (errors at 95 CL): sterile neutrino mass
6.08 \pm 3.22 keV, mixing angle \sin^2 2 \theta < 5.61 x 10^{-10}, lepton
number per flavor L_4 = 1.23 \pm 0.04 and sterile neutrino mass fraction f_\nu
< 0.078. Our results are in good agreement with the sterile neutrino resonant
production parameters inferred in Ref. [62] from the linear large scale
structure constraints to produce full Dark Matter density.
