Can decaying sterile neutrinos account for all dark matter?

The recent discovery of unexplained X-ray line of $3.5-3.6$ keV emitted from the Perseus cluster of galaxies and M31 and the excess X-ray line of $8.7$ keV emitted from the Milky Way center may indicate that dark matter would decay. In this article, I show that approximately 80 \% of dark matter being 7.1 keV sterile neutrinos and 20 \% of dark matter being 17.4 keV sterile neutrinos can satisfactorily explain the observed X-ray lines and account for all missing mass. No free parameter is needed in this model. This scenario is also compatible with current robust observational constraints from the matter power spectrum in large-scale structures and would alleviate the challenges faced by the existing dark matter models.