Page "Make (software)" Paragraph 14

Make decides whether a target needs to be regenerated by comparing file modification times.

This solves the problem of avoiding the building of files which are already up to date, but it fails when a file changes but its modification time stays in the past.

Such changes could be caused by restoring an older version of a source file, or when a network filesystem is a source of files and its clock or timezone is not synchronized with the machine running Make.

The user must handle this situation by forcing a complete build.

Conversely, if a source file's modification time is in the future, it triggers unnecessary rebuilding, which may inconvenience users.