User-Level Checkpointing

Many application programs, especially programs that consume considerable CPU time, use checkpointing and restart mechanisms to increase fault tolerance. Status information and important parts of the processed data are repeatedly written to one or more files at certain stages of the algorithm. If the application is aborted, these restart files can be processed and restarted at a later time. The files reach a consistent state that is comparable to the situation just before the checkpoint. Because the user mostly has to move the restart files to a proper location, this kind of checkpointing is called user-level checkpointing.

Application programs that do not have integrated user-level checkpointing can use a checkpointing library. A checkpointing library can be provided by some hardware vendors or by the public domain. The Condor project of the University of Wisconsin is an example. By relinking an application with such a library, a checkpointing mechanism is installed in the application without requiring source code changes.