+.\"
+.SS The sempid value
+POSIX.1 defines
+.I sempid
+as the "process ID of [the] last operation" on a semaphore,
+and explicitly notes that this value is set by a successful
+.BR semop (2)
+call, with the implication that no other interface affects the
+.I sempid
+value.
+.PP
+While some implementations conform to the behavior specified in POSIX.1,
+others do not.
+(The fault here probably lies with POSIX.1 inasmuch as it likely failed
+to capture the full range of existing implementation behaviors.)
+Various other implementations
+.\" At least OpenSolaris (and, one supposes, older Solaris) and Darwin
+also update
+.I sempid
+for the other operations that update the value of a semaphore: the
+.B SETVAL
+and
+.B SETALL
+operations, as well as the semaphore adjustments performed
+on process termination as a consequence of the use of the
+.B SEM_UNDO
+flag (see
+.BR semop (2)).
+.PP
+Linux also updates
+.I sempid
+for
+.BR SETVAL
+operations and semaphore adjustments.
+However, somewhat inconsistently, up to and including 4.5,
+Linux did not update
+.I sempid
+for
+.BR SETALL
+operations.
+This was rectified
+.\" commit a5f4db877177d2a3d7ae62a7bac3a5a27e083d7f
+in Linux 4.6.
+.SH SEE ALSO