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       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/shm.h — XSI shared memory facility


       #include <sys/shm.h>


       The <sys/shm.h> header shall define the following symbolic constants:

       SHM_RDONLY  Attach read-only (else read-write).

       SHM_RND     Round attach address to SHMLBA.

       SHMLBA      Segment low boundary address multiple.

       The <sys/shm.h> header shall define the following data types through typedef:

       shmatt_t    Unsigned  integer used for the number of current attaches that must be able to
                   store values at least as large as a type unsigned short.

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

           struct ipc_perm shm_perm   Operation permission structure.
           size_t          shm_segsz  Size of segment in bytes.
           pid_t           shm_lpid   Process ID of last shared memory operation.
           pid_t           shm_cpid   Process ID of creator.
           shmatt_t        shm_nattch Number of current attaches.
           time_t          shm_atime  Time of last shmat().
           time_t          shm_dtime  Time of last shmdt().
           time_t          shm_ctime  Time of last change by shmctl().

       The  <sys/shm.h>  header  shall define the pid_t, size_t, and time_t types as described in

       The following shall be declared as functions and may also be defined as  macros.  Function
       prototypes shall be provided.

           void *shmat(int, const void *, int);
           int   shmctl(int, int, struct shmid_ds *);
           int   shmdt(const void *);
           int   shmget(key_t, size_t, int);

       In addition, the <sys/shm.h> header shall include the <sys/ipc.h> header.

       The following sections are informative.








       <sys_ipc.h>, <sys_types.h>

       The System Interfaces volume of POSIX.1‐2008, shmat(), shmctl(), shmdt(), shmget()


       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
       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 .

       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 .