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[thirdparty/man-pages.git] / man2 / msgget.2

diff --git a/man2/msgget.2 b/man2/msgget.2
index cc7f35525594c74143f5c434638acf85d3cb7a89..b7b95b66e4d575d37b4e66eb9d05e0dc3f77e50b 100644 (file)
--- a/man2/msgget.2
+++ b/man2/msgget.2
@@ -1,7 +1,8 @@
 .\" Copyright 1993 Giorgio Ciucci <giorgio@crcc.it>
 .\"
+.\" %%%LICENSE_START(VERBATIM)
 .\" Permission is granted to make and distribute verbatim copies of this
-.\" manual provflags the copyright notice and this permission notice are
+.\" manual provided the copyright notice and this permission notice are
 .\" preserved on all copies.
 .\"
 .\" Permission is granted to copy and distribute modified versions of this
@@ -19,6 +20,7 @@
 .\"
 .\" Formatted or processed versions of this manual, if unaccompanied by
 .\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
 .\"
 .\" Added correction due to Nick Duffek <nsd@bbc.com>, aeb, 960426
 .\" Modified Wed Nov  6 04:00:31 1996 by Eric S. Raymond <esr@thyrsus.com>
@@ -30,24 +32,33 @@
 .\"    Language and formatting clean-ups
 .\"    Added notes on /proc files
 .\"
-.TH MSGGET 2 2004-05-27 "Linux" "Linux Programmer's Manual"
+.TH MSGGET 2 2019-08-02 "Linux" "Linux Programmer's Manual"
 .SH NAME
-msgget \- get a message queue identifier
+msgget \- get a System V message queue identifier
 .SH SYNOPSIS
 .nf
 .B #include <sys/types.h>
 .B #include <sys/ipc.h>
 .B #include <sys/msg.h>
-.fi
-.sp
+.PP
 .BI "int msgget(key_t " key ", int " msgflg );
+.fi
 .SH DESCRIPTION
 The
 .BR msgget ()
-system call returns the message queue identifier associated
+system call returns the System\ V message queue identifier associated
 with the value of the
 .I key
 argument.
+It may be used either to obtain the identifier of a previously created
+message queue (when
+.I msgflg
+is zero and
+.I key
+does not have the value
+.BR IPC_PRIVATE ),
+or to create a new set.
+.PP
 A new message queue is created if
 .I key
 has the value
@@ -117,7 +128,7 @@ are set to the least significant 9 bits of
 .IR msg_qnum ,
 .IR msg_lspid ,
 .IR msg_lrpid ,
-.I msg_stime
+.IR msg_stime ,
 and
 .I msg_rtime
 are set to 0.
@@ -132,9 +143,9 @@ is set to the system limit
 If the message queue already exists the permissions are
 verified, and a check is made to see if it is marked for
 destruction.
-.SH "RETURN VALUE"
+.SH RETURN VALUE
 If successful, the return value will be the message queue identifier (a
-non-negative integer), otherwise \-1
+nonnegative integer), otherwise \-1
 with
 .I errno
 indicating the error.
@@ -142,24 +153,23 @@ indicating the error.
 On failure,
 .I errno
 is set to one of the following values:
-.TP 11
+.TP
 .B EACCES
 A message queue exists for
 .IR key ,
 but the calling process does not have permission to access the queue,
 and does not have the
 .B CAP_IPC_OWNER
-capability.
+capability in the user namespace that governs its IPC namespace.
 .TP
 .B EEXIST
-A message queue exists for
-.I key
-and
-.I msgflg
-specified both
 .B IPC_CREAT
 and
-.BR IPC_EXCL .
+.BR IPC_EXCL
+were specified in
+.IR msgflg ,
+but a message queue already exists for
+.IR key .
 .TP
 .B ENOENT
 No message queue exists for
@@ -178,9 +188,22 @@ A message queue has to be created but the system limit for the maximum
 number of message queues
 .RB ( MSGMNI )
 would be exceeded.
-.SH "CONFORMING TO"
-SVr4, POSIX.1-2001.
+.SH CONFORMING TO
+POSIX.1-2001, POSIX.1-2008, SVr4.
 .SH NOTES
+The inclusion of
+.I <sys/types.h>
+and
+.I <sys/ipc.h>
+isn't required on Linux or by any version of POSIX.
+However,
+some old implementations required the inclusion of these header files,
+and the SVID also documented their inclusion.
+Applications intended to be portable to such old systems may need
+to include these header files.
+.\" Like Linux, the FreeBSD man pages still document
+.\" the inclusion of these header files.
+.PP
 .B IPC_PRIVATE
 isn't a flag field but a
 .I key_t
@@ -194,14 +217,18 @@ and creates a new message queue (on success).
 The following is a system limit on message queue resources affecting a
 .BR msgget ()
 call:
-.TP 11
+.TP
 .B MSGMNI
-System wide maximum number of message queues: policy
-dependent
-(on Linux, this limit can be read and modified via
-.IR /proc/sys/kernel/msgmni ).
-.SS "Linux Notes"
-Until version 2.3.20 Linux would return
+System-wide limit on the number of message queues.
+Before Linux 3.19,
+.\" commit 0050ee059f7fc86b1df2527aaa14ed5dc72f9973
+the default value for this limit was calculated using a formula
+based on available system memory.
+Since Linux 3.19, the default value is 32,000.
+On Linux, this limit can be read and modified via
+.IR /proc/sys/kernel/msgmni .
+.SS Linux notes
+Until version 2.3.20, Linux would return
 .B EIDRM
 for a
 .BR msgget ()
@@ -212,11 +239,11 @@ The name choice
 was perhaps unfortunate,
 .B IPC_NEW
 would more clearly show its function.
-.SH "SEE ALSO"
+.SH SEE ALSO
 .BR msgctl (2),
 .BR msgrcv (2),
 .BR msgsnd (2),
 .BR ftok (3),
 .BR capabilities (7),
 .BR mq_overview (7),
-.BR svipc (7)
+.BR sysvipc (7)