sys_msg.h(7POSIX) POSIX Programmer's Manual sys_msg.h(7POSIX)
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of
this interface may differ (consult the corresponding Linux manual page for details of
Linux behavior), or the interface may not be implemented on Linux.
sys/msg.h — XSI message queue structures
The <sys/msg.h> header shall define the following data types through typedef:
msgqnum_t Used for the number of messages in the message queue.
msglen_t Used for the number of bytes allowed in a message queue.
These types shall be unsigned integer types that are able to store values at least as
large as a type unsigned short.
The <sys/msg.h> header shall define the following symbolic constant as a message operation
MSG_NOERROR No error if big message.
The <sys/msg.h> header shall define the msqid_ds structure, which shall include the fol‐
struct ipc_perm msg_perm Operation permission structure.
msgqnum_t msg_qnum Number of messages currently on queue.
msglen_t msg_qbytes Maximum number of bytes allowed on queue.
pid_t msg_lspid Process ID of last msgsnd().
pid_t msg_lrpid Process ID of last msgrcv().
time_t msg_stime Time of last msgsnd().
time_t msg_rtime Time of last msgrcv().
time_t msg_ctime Time of last change.
The <sys/msg.h> header shall define the pid_t, size_t, ssize_t, and time_t types as
described in <sys/types.h>.
The following shall be declared as functions and may also be defined as macros. Function
prototypes shall be provided.
int msgctl(int, int, struct msqid_ds *);
int msgget(key_t, int);
ssize_t msgrcv(int, void *, size_t, long, int);
int msgsnd(int, const void *, size_t, int);
In addition, the <sys/msg.h> header shall include the <sys/ipc.h> header.
The following sections are informative.
The System Interfaces volume of POSIX.1‐2008, msgctl(), msgget(), msgrcv(), msgsnd()
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrep‐
ancy between this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original Standard can be
obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are most likely to have
been introduced during the conversion of the source files to man page format. To report
such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 sys_msg.h(7POSIX)