  We aim to understand the interplay between non-radial oscillations and
stellar magnetic activity and test the feasibility of doing asteroseismology of
magnetically active stars. We analyze 30 years of photometric time-series data,
3 years of HARPS radial velocity monitoring, and 3 nights of high-cadence HARPS
asteroseismic data. We construct a high-S/N HARPS spectrum that we use to
determine atmospheric parameters and chemical composition. Spectra observed at
different rotation phases are analyzed to search for signs of temperature or
abundance variations. An upper limit on the projected rotational velocity is
derived from very high-resolution CES spectra. We detect oscillations in EK Eri
with a frequency of the maximum power of nu_max = 320+/-32 muHz, and we derive
a peak amplitude per radial mode of ~0.15 m/s, which is a factor of ~3 lower
than expected. We suggest that the magnetic field may act to suppress
low-degree modes. Individual frequencies can not be extracted from the
available data. We derive accurate atmospheric parameters, refining our
previous analysis. We confirm that the main light variation is due to cool
spots, but that other contributions may need to be taken into account. We
suggest that the rotation period is twice the photometric period, i.e., P_rot =
2 P_phot = 617.6 d. We conclude from our derived parameters that v sin i < 0.40
km/s. We also link the time series of direct magnetic field measurements
available in the literature to our newly derived photometric ephemeris.
