exits with a return value of B<0> for I<success>, B<1> for I<warning> and B<2>
for I<critical>. If the values are not available or some other error occurred,
it returns B<3> for I<unknown>.
exits with a return value of B<0> for I<success>, B<1> for I<warning> and B<2>
for I<critical>. If the values are not available or some other error occurred,
it returns B<3> for I<unknown>.