Abstract: The paper describes our experience with the implementation and applications of the Unix checkpointing library libckp, and identifies two concepts that have proven to be the key to making checkpointing a powerful tool. First, including all persistent states, i.e., user files, as part of the process state that can be checkpointed and recovered provides a truly transparent and consistent rollback. Second, excluding part of the persistent state from the process state allows user programs to process future inputs from a desirable state, which leads to interesting new applications of checkpointing. We use real-life examples to demonstrate the use of libckp for bypassing premature software exits, for fast initialization and for memory rejuvenation.