shmget(2)                 SYSTEM CALLS                  shmget(2)



NAME
     shmget - get shared memory segment identifier

SYNOPSIS
     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/shm.h>

     int shmget(keyt key, int size, int shmflg);

DESCRIPTION
     shmget 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:

          key is equal to IPCPRIVATE.

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

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

          shmperm.cuid,   shmperm.uid,    shmperm.cgid,    and
          shmperm.gid are set equal to the effective user ID and
          effective group ID, respectively, of the  calling  pro-
          cess.

          The access permission bits  of  shmperm.mode  are  set
          equal   to   the  access  permission  bits  of  shmflg.
          shmsegsz is set equal to the value of size.

          shmlpid, shmnattch shmatime, and shmdtime  are  set
          equal to 0.

          shmctime is set equal to the current time.

     shmget fails if one or more of the following are true:

     EINVAL         size is less than the system-imposed  minimum
                    or greater than the system-imposed maximum.

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

     EINVAL         A shared memory identifier exists for key but
                    the size of the segment associated with it is



                                                                1

shmget(2)                 SYSTEM CALLS                  shmget(2)



                    less than size and size is not equal to zero.

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

     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.

     ENOMEM         A shared  memory  identifier  and  associated
                    shared  memory  segment are to be created but
                    the amount of available memory is not  suffi-
                    cient to fill the request.

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

SEE ALSO
     intro(2), shmctl(2), shmop(2), stdipc(3C).

DIAGNOSTICS
     Upon successful completion, a non-negative integer, namely a
     shared memory identifier is returned.  Otherwise, a value of
     -1 is returned and errno is set to indicate the error.

NOTES
     The user must explicitly remove shared memory segments after
     the last reference to them has been removed.

























                                                                2