I know that there are (at least) two types of message queues: System V message queues and POSIX message queue. To my surprise, the man page also says that the msgget system call for System V message queues, for example,


POSIX.1-2001, POSIX.1-2008, SVr4.

Since System V message queques conformed to POSIX, why did the POSIX organization bother to invent so-called POSIX message queues that were different from System V message queues?

  • Side note: There's an excellent overview of the historical development of Unix branches in Michael Kerrisk's The Linux Programming Interface, which is a very recommandable supplement to the man pages and would be a good start for you to dig into the details. – Murphy Dec 19 '17 at 10:08

System V message queues predate POSIX. They were adopted by POSIX probably over a decade after they were introduced in System V Unix. The "POSIX message queues" were introduced relatively recently and were invented because of dislike (at least by some) of the System V implementation.

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