NAME

       shmget — obtain a shared memory identifier

LIBRARY

       Standard C Library (libc, -lc)

SYNOPSIS

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

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

DESCRIPTION

       Based  on  the  values  of key and flag, shmget() returns the identifier of a newly created or previously
       existing shared memory segment.  The key is analogous to a filename: it provides a handle that  names  an
       IPC object.  There are three ways to specify a key:

       •   IPC_PRIVATE may be specified, in which case a new IPC object will be created.

       •   An  integer  constant  may  be specified.  If no IPC object corresponding to key is specified and the
           IPC_CREAT bit is set in flag, a new one will be created.

       •   The ftok(3) may be used to generate a key from a pathname.

       The mode of a newly created IPC object is determined by OR'ing the  following  constants  into  the  flag
       argument:

       S_IRUSR       Read access for owner.

       S_IWUSR       Write access for owner.

       S_IRGRP       Read access for group.

       S_IWGRP       Write access for group.

       S_IROTH       Read access for other.

       S_IWOTH       Write access for other.

       When  creating  a new shared memory segment, size indicates the desired size of the new segment in bytes.
       The size of the segment may be rounded up to a multiple convenient to the kernel (i.e., the page size).

RETURN VALUES

       Upon successful completion, shmget() returns the positive integer identifier of a shared memory  segment.
       Otherwise, -1 is returned and errno set to indicate the error.

ERRORS

       The shmget() system call will fail if:

       [EINVAL]           Size  specified  is  greater  than  the size of the previously existing segment.  Size
                          specified is less than the system imposed minimum, or greater than the system  imposed
                          maximum.

       [ENOENT]           No shared memory segment was found matching key, and IPC_CREAT was not specified.

       [ENOSPC]           The kernel was unable to allocate enough memory to satisfy the request.

       [EEXIST]           IPC_CREAT  and  IPC_EXCL  were specified, and a shared memory segment corresponding to
                          key already exists.

SEE ALSO

       shmat(2), shmctl(2), shmdt(2), stat(2), ftok(3)

Debian                                          December 17, 2010                                      SHMGET(2)