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## Interrupting or Killing `make`

If `make` gets a fatal signal while a command is executing, it may delete the target file that the command was supposed to update. This is done if the target file's last-modification time has changed since `make` first checked it.

The purpose of deleting the target is to make sure that it is remade from scratch when `make` is next run. Why is this? Suppose you type `Ctrl-c` while a compiler is running, and it has begun to write an object file ``foo.o'`. The `Ctrl-c` kills the compiler, resulting in an incomplete file whose last-modification time is newer than the source file ``foo.c'`. But `make` also receives the `Ctrl-c` signal and deletes this incomplete file. If `make` did not do this, the next invocation of `make` would think that ``foo.o'` did not require updating--resulting in a strange error message from the linker when it tries to link an object file half of which is missing.

You can prevent the deletion of a target file in this way by making the special target `.PRECIOUS` depend on it. Before remaking a target, `make` checks to see whether it appears on the dependencies of `.PRECIOUS`, and thereby decides whether the target should be deleted if a signal happens. Some reasons why you might do this are that the target is updated in some atomic fashion, or exists only to record a modification-time (its contents do not matter), or must exist at all times to prevent other sorts of trouble.

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