The POSIX standard, developed 25 years ago, comprises
a set of operating system (OS) abstractions that aid application
portability across UNIX-based OSes.
While OSes and applications have evolved tremendously over the last
25 years, POSIX, and the basic set of abstractions it provides,
has remained largely unchanged. Little has been done
to measure how and to what extent traditional POSIX abstractions
are being used in modern OSes, and whether new
abstractions are taking form, dethroning traditional ones.We
explore these questions through a study of POSIX usage
in modern desktop and mobile OSes: Android, OS X, and
Ubuntu. Our results show that new abstractions are taking
form, replacing several prominent traditional abstractions in
POSIX. While the changes are driven by common needs and
are conceptually similar across the three OSes, they are not
converging on any new standard, increasing fragmentation.