PROLOG

       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.

NAME

       sys/msg.h — XSI message queue structures

SYNOPSIS

       #include <sys/msg.h>

DESCRIPTION

       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
       flag:

       MSG_NOERROR   No error if big message.

       The  <sys/msg.h>  header  shall  define  the  msqid_ds  structure, which shall include the
       following members:

           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.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       <sys_ipc.h>, <sys_types.h>

       The System Interfaces volume of POSIX.1‐2017, msgctl(), msgget(), msgrcv(), msgsnd()

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1-2017,  Standard  for  Information Technology -- Portable Operating System Interface
       (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C)  2018  by
       the  Institute  of  Electrical  and Electronics Engineers, Inc and The Open Group.  In the
       event of any discrepancy 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.opengroup.org/unix/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 .