Atomic Rename
A rename operation that, under the appropriate same-filesystem conditions, appears to observers as a single namespace transition without an intermediate target name state.
Writing to a temporary file and then using rename() to publish the final name is a common way to keep readers from observing partially written content. The atomic property belongs to the namespace transition, not to the process that produced the bytes.
Two limits matter in practice: moves across filesystems do not have the same semantics, and atomic visibility is not the same as crash durability. fsync() and directory synchronization remain separate concerns, as discussed in atomic file publication.