Manual Pages for UNIX Operating System command usage for man shmget

System Calls                                            shmget(2)



NAME
     shmget - get shared memory segment identifier

SYNOPSIS
     #include 
     #include 
     #include 

     int shmget(key_t key, size_t size, int shmflg);


DESCRIPTION
     The shmget() function returns the shared  memory  identifier
     associated with key.


     A shared memory identifier and associated data structure and
     shared  memory segment of at least size bytes (see Intro(2))
     are created for key if one of the following are true:

         o    The key argument is equal to IPC_PRIVATE.

         o    The key argument does not  already  have  a  shared
              memory   identifier   associated   with   it,   and
              (shmflg&IPC_CREAT) is true.


     Upon creation, the data structure associated  with  the  new
     shared memory identifier is initialized as follows:

         o    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.

         o    The access permission bits of shm_perm.mode are set
              equal  to  the  access  permission  bits of shmflg.
              shm_segsz is set equal to the value of size.

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

         o    The shm_ctime is set equal to the current time.


     Shared memory segments must be explicitly removed after  the
     last reference to them has been removed.

RETURN VALUES
     Upon   successful   completion,   a   non-negative   integer
     representing  a shared memory identifier is returned. Other-
     wise, -1 is returned and errno is set to indicate the error.



SunOS 5.11          Last change: 14 Aug 2006                    1






System Calls                                            shmget(2)



ERRORS
     The shmget() function will fail if:

     EACCES    A shared memory  identifier  exists  for  key  but
               operation  permission  (see Intro(2)) as specified
               by the low-order 9 bits of  shmflg  would  not  be
               granted.


     EEXIST    A shared memory identifier exists for key but both
               (shmflg&IPC_CREAT) and (shmflg&IPC_EXCL) are true.


     EINVAL    The size argument is less than the  system-imposed
               minimum  or  greater  than the system-imposed max-
               imum. See NOTES.

               A shared memory identifier exists for key but  the
               size  of  the  segment  associated with it is less
               than size and size is not equal to 0.


     ENOENT    A shared memory identifier does not exist for  key
               and (shmflg&IPC_CREAT) is false.


     ENOMEM    A shared memory identifier and  associated  shared
               memory segment are to be created but the amount of
               available 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. See NOTES.


ATTRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:














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System Calls                                            shmget(2)



     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Interface Stability         | Committed                   |
    |_____________________________|_____________________________|
    | Standard                    | See standards(5).           |
    |_____________________________|_____________________________|


SEE ALSO
     rctladm(1M),  Intro(2),  setrctl(2),  shmctl(2),   shmop(2),
     ftok(3C), getpagesize(3C), attributes(5), standards(5)

NOTES
     The project.max-shm-memory resource  control  restricts  the
     total  amount  of  shared memory a project can allocate. The
     zone.max-shm-memory resource  control  restricts  the  total
     amount of shared memory that can be allocated by a zone. The
     system-imposed maximum on the size of a shared  memory  seg-
     ment  is  therefore  a   function  of the sizes of any other
     shared memory segments the calling project might have  allo-
     cated  that  are  still  in use, as well as any other shared
     memory segments allocated and still in use by  processes  in
     the  zone.   For  accounting  purposes,  segment  sizes  are
     rounded up to the nearest multiple of the system page  size.
     See getpagesize(3C).


     The system-imposed limit on  the  number  of  shared  memory
     identifiers  is  maintained on a per-project basis using the
     project.max-shm-ids resource control.  The  zone.max-shm-ids
     resource control restricts the total number of shared memory
     identifiers that can be allocated by a zone.


     See rctladm(1M) and setrctl(2) for information  about  using
     resource controls.


















SunOS 5.11          Last change: 14 Aug 2006                    3