No matter if your simulation simply takes a lot of time or it has crashed previously, restarting is an important feature of a simulation software. preCICE has currently no restart mode (we had one previously, but this is a long story). The good thing is: You don’t need a restart mode in preCICE to restart a coupled simulation! It is sufficient if both your solvers are able to restart.
To restart a coupled simulation, simply start preCICE normally. Use initializeData to communicate the values from where you restart. Look at the the page Step 7 - Data initialization | preCICE - The Coupling Library to learn how to do this exactly. The only downside is that the preCICE output starts counting from time 0 again and that preCICE output files (vtk, iteration-files, convergence-files, …) might get overwritten (store them away first!). Also, the quasi-Newton scheme (if you use one) starts from an empty column space again.
Please let us know if this kind of restart is not sufficient for you and we try to add restart features (again).
(transferred from the old preCICE Wiki)
See also related topics here, such as Restarting coupled FSI simulation with preCICE.