trusty (3) shmget.3posix.gz

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  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 shmget() function shall return the shared memory identifier associated with key.

       A  shared  memory identifier, associated data structure, and shared memory 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  equal  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 equal to the low-order nine bits of shmflg.

        * The value of shm_segsz is set equal to the value of size.

        * The values of shm_lpid, shm_nattch, shm_atime, and shm_dtime are set equal to 0.

        * The value of shm_ctime is set equal to the current time.

       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  integer,  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 permission as specified by  the  low-order
              nine bits of shmflg would not be granted; see XSI Interprocess Communication .

       EEXIST A  shared  memory  identifier  exists  for  the  argument  key  but  (shmflg &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 system-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 and size is not 0.

       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 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 , shmat() , shmctl() , shmdt() , shm_open()  ,  shm_unlink()  ,
       the Base Definitions 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 Technology -- 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 .