  We report a characterization of the multi-band flux variability and
correlations of the nearby (z=0.031) blazar Markarian 421 (Mrk 421) using data
from Mets\"{a}hovi, Swift, Fermi-LAT, MAGIC, FACT and other collaborations and
instruments from November 2014 till June 2016. Mrk 421 did not show any
prominent flaring activity, but exhibited periods of historically low activity
above 1 TeV (F$_{>1\mathrm{TeV}}<$ 1.7$\times$10$^{-12}$ ph cm$^{-2}$ s$^{-1}$)
and in the 2-10 keV (X-ray) band (F$_{2-10 \mathrm{keV}}<$3.6$\times$10$^{-11}$
erg cm$^{-2}$ s$^{-1}$), during which the Swift-BAT data suggests an additional
spectral component beyond the regular synchrotron emission. The highest flux
variability occurs in X-rays and very-high-energy (E$>$0.1 TeV) $\gamma$-rays,
which, despite the low activity, show a significant positive correlation with
no time lag. The HR$_\mathrm{keV}$ and HR$_\mathrm{TeV}$ show the
harder-when-brighter trend observed in many blazars, but the trend flattens at
the highest fluxes, which suggests a change in the processes dominating the
blazar variability. Enlarging our data set with data from years 2007 to 2014,
we measured a positive correlation between the optical and the GeV emission
over a range of about 60 days centered at time lag zero, and a positive
correlation between the optical/GeV and the radio emission over a range of
about 60 days centered at a time lag of $43^{+9}_{-6}$ days.This observation is
consistent with the radio-bright zone being located about 0.2 parsec downstream
from the optical/GeV emission regions of the jet. The flux distributions are
better described with a LogNormal function in most of the energy bands probed,
indicating that the variability in Mrk 421 is likely produced by a
multiplicative process.
