Removes one file if it is a regular file older than the grace period.
Anything that will not open — a symlink refused by `O_NOFOLLOW`, a
file another process holds exclusively — is left alone, because its age
cannot be established and an unaged file might still be in use. A file
whose descriptor would not close is left alone for the same reason: the
inspection did not finish cleanly, and the next sweep will try again.
Removes one file if it is a regular file older than the grace period.
Anything that will not open — a symlink refused by `O_NOFOLLOW`, a file another process holds exclusively — is left alone, because its age cannot be established and an unaged file might still be in use. A file whose descriptor would not close is left alone for the same reason: the inspection did not finish cleanly, and the next sweep will try again.