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SHMGET(3P)                 POSIX Programmer's Manual                SHMGET(3P)
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
       shmget -- get an XSI shared memory segment
SYNOPSIS
       #include <sys/shm.h>
       int shmget(key_t key, size_t size, int shmflg);
DESCRIPTION
       The shmget() function operates on XSI shared memory (see the Base Defi-
       nitions  volume  of POSIX.1-2008, Section 3.342, Shared Memory Object).
       It is unspecified whether this function interoperates with the realtime
       interprocess communication facilities defined in Section 2.8, Realtime.
       The shmget() function shall return the shared memory identifier associ-
       ated with key.
       A shared memory identifier, associated data structure, and shared  mem-
       ory  segment  of  at least size bytes (see <sys/shm.h>) are created for
       key if one of the following is true:
        *  The argument key is equal to IPC_PRIVATE.
        *  The argument key does not already have a shared  memory  identifier
           associated with it and (shmflg &IPC_CREAT) is non-zero.
       Upon creation, the data structure associated with the new shared memory
       identifier shall be initialized as follows:
        *  The  values  of  shm_perm.cuid,  shm_perm.uid,  shm_perm.cgid,  and
           shm_perm.gid  are  set to the effective user ID and effective group
           ID, respectively, of the calling process.
        *  The low-order nine bits of shm_perm.mode are set to  the  low-order
           nine bits of shmflg.
        *  The value of shm_segsz is set to the value of size.
        *  The  values  of  shm_lpid, shm_nattch, shm_atime, and shm_dtime are
           set to 0.
        *  The value of shm_ctime is set to the current time, as described  in
           Section 2.7.1, IPC General Description.
       When the shared memory segment is created, it shall be initialized with
       all zero values.
RETURN VALUE
       Upon successful completion, shmget() shall return a non-negative  inte-
       ger,  namely  a shared memory identifier; otherwise, it shall return -1
       and set errno to indicate the error.
ERRORS
       The shmget() function shall fail if:
       EACCES A shared memory identifier exists for key but operation  permis-
              sion as specified by the low-order nine bits of shmflg would not
              be granted; see Section 2.7, XSI Interprocess Communication.
       EEXIST A shared memory identifier exists for the argument key but (shm-
              flg &IPC_CREAT) &&(shmflg &IPC_EXCL) is non-zero.
       EINVAL A  shared  memory segment is to be created and the value of size
              is less than the system-imposed minimum or greater than the sys-
              tem-imposed maximum.
       EINVAL No  shared  memory  segment is to be created and a shared memory
              segment exists for key but the size of  the  segment  associated
              with it is less than size.
       ENOENT A  shared  memory identifier does not exist for the argument key
              and (shmflg &IPC_CREAT) is 0.
       ENOMEM A shared memory identifier and associated shared memory  segment
              shall be created, but the amount of available physical memory is
              not sufficient to fill the request.
       ENOSPC A shared memory identifier is to be  created,  but  the  system-
              imposed  limit  on  the  maximum number of allowed shared memory
              identifiers system-wide would be exceeded.
       The following sections are informative.
EXAMPLES
       None.
APPLICATION USAGE
       The POSIX Realtime Extension defines alternative interfaces for  inter-
       process  communication.  Application  developers  who  need  to use IPC
       should design their applications so that modules using the IPC routines
       described  in Section 2.7, XSI Interprocess Communication can be easily
       modified to use the alternative interfaces.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       Section 2.7, XSI Interprocess  Communication,  Section  2.8,  Realtime,
       ftok(), shmat(), shmctl(), shmdt(), shm_open(), shm_unlink()
       The Base Definitions volume of POSIX.1-2008, Section 3.342, Shared Mem-
       ory Object, <sys_shm.h>
COPYRIGHT
       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 Electri-
       cal 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 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.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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                           SHMGET(3P)