Added (brief) description of SHM_HUGETLB.

man2/shmget.2

@@ -109,7 +109,12 @@ meaning, as the
 argument of
 .BR open (2).
 Presently, the execute permissions are not used by the system.
-.\" FIXME -- document SHM_HUGETLB -- see Documentation/vm/hugetlbpage.txt
+.TP
+.B SHM_HUGETLB
+Allocate the segment using "huge pages."  
+See the kernel source file
+.I Documentation/vm/hugetlbpage.txt
+for further information.
 .PP
 If a new shared memory segment is created,
 then its associated data structure
@@ -212,6 +217,13 @@ or allocating a segment of the requested
 .I size
 would cause the system to exceed the system-wide limit on shared memory
 .RB ( SHMALL ).
+.TP
+.B EPERM
+The
+.B SHM_HUGETLB
+flag was specified, but the caller was not privileged (did not have the
+.B CAP_IPC_LOCK
+capability).
 .SH NOTES
 .B IPC_PRIVATE
 isn't a flag field but a
@@ -261,6 +273,9 @@ SVr4, SVID.  SVr4 documents an additional error condition EEXIST.
 Until version 2.3.30 Linux would return EIDRM for a
 .BR shmget ()
 on a shared memory segment scheduled for deletion.
+
+.B SHM_HUGETLB
+is a non-portable Linux extension.
 .SH "SEE ALSO"
 .BR shmat (2),
 .BR shmctl (2),