  The paper proposes a method of finding the beam loss locations in a linac. If
the beam is scraped at an aperture limitation, moving its centroid with two
dipole correctors located upstream and oscillating in sync produces a line at
the corresponding frequency in spectra of current-sensitive devices downstream
of the loss point. The phase of this signal contains information about the
location of the beam loss. Similar lines appear also in the position signals of
Beam Position Monitors (BPMs). The phases of the BPM position lines change
monotonically (within each 2{\pi}) along the linac and can be used a reference
system. The phase of the loss signal compared with this reference system
pinpoints the beam loss location, assuming that longitudinal coordinates of the
BPMs are known. If the correctors deflection amplitudes and the phase offset
between their waveforms are chosen optimally and well calibrated, the same
measurement provides values of the \b{eta}-function and the betatron phase
advance at the BPM locations. Optics measurements of this type can be made
parasitically, with negligible effect on the emittance, if a long measurement
time is acceptable.
