SHMAT(3P)						     POSIX Programmer's Manual							 SHMAT(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       shmat - XSI shared memory attach operation

SYNOPSIS

       #include <sys/shm.h>

       void *shmat(int shmid, const void *shmaddr, int shmflg);

DESCRIPTION

       The shmat() function operates on XSI shared memory (see the Base Definitions volume of IEEE Std 1003.1-2001, Section 3.340,  Shared  Memory
       Object).  It is unspecified whether this function interoperates with the realtime interprocess communication facilities defined in Realtime
       .

       The shmat() function attaches the shared memory segment associated with the shared memory identifier specified  by  shmid  to  the  address
       space of the calling process. The segment is attached at the address specified by one of the following criteria:

	* If shmaddr is a null pointer, the segment is attached at the first available address as selected by the system.

	* If  shmaddr  is  not	a  null  pointer  and  (shmflg	&SHM_RND)  is  non-zero,  the segment is attached at the address given by (shmaddr
	  -((uintptr_t)shmaddr %SHMLBA)).  The character '%' is the C-language remainder operator.

	* If shmaddr is not a null pointer and (shmflg &SHM_RND) is 0, the segment is attached at the address given by shmaddr.

	* The segment is attached for reading if (shmflg &SHM_RDONLY) is non-zero and the calling process has read permission; otherwise, if it is
	  0 and the calling process has read and write permission, the segment is attached for reading and writing.

RETURN VALUE

       Upon  successful  completion, shmat() shall increment the value of shm_nattch in the data structure associated with the shared memory ID of
       the attached shared memory segment and return the segment's start address.

       Otherwise, the shared memory segment shall not be attached, shmat() shall return -1, and errno shall be set to indicate the error.

ERRORS

       The shmat() function shall fail if:

       EACCES Operation permission is denied to the calling process; see XSI Interprocess Communication .

       EINVAL The value of shmid is not a valid shared memory identifier,  the	shmaddr  is  not  a  null  pointer,  and  the  value  of  (shmaddr
	      -((uintptr_t)shmaddr  %SHMLBA))  is  an  illegal	address for attaching shared memory; or the shmaddr is not a null pointer, (shmflg
	      &SHM_RND) is 0, and the value of shmaddr is an illegal address for attaching shared memory.

       EMFILE The number of shared memory segments attached to the calling process would exceed the system-imposed limit.

       ENOMEM The available data space is not large enough to accommodate the shared memory segment.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       The POSIX Realtime Extension defines alternative interfaces for interprocess communication. Application developers  who	need  to  use  IPC
       should  design their applications so that modules using the IPC routines described in XSI Interprocess Communication can be easily modified
       to use the alternative interfaces.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       XSI Interprocess Communication, Realtime, exec() , exit(), fork(), shmctl(), shmdt(), shmget(), shm_open(), shm_unlink(), the Base  Defini-
       tions volume of IEEE Std 1003.1-2001, <sys/shm.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .

IEEE
/The Open Group						       2003								 SHMAT(3P)