#include <sys/shm.h> int
shmget (key_t key size_t size int flag);
Based on the values of
Fa flag ,
returns the identifier of a newly created or previously existing shared
is analogous to a filename: it provides a handle that names an
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
is specified and the IPC_CREAT bit is set in
Fa flag ,
a new one will be created.
may be used to generate a key from a pathname.
The mode of a newly created IPC object is determined by
the following constants into the
Read access for user.
Write access for user.
Read access for group.
Write access for group.
Read access for other.
Write access for other.
When creating a new shared memory segment,
indicates the desired size of the new segment in bytes.
of the segment may be rounded up to a multiple convenient to the
kernel (i.e., the page size).
Upon successful completion,
returns the positive integer identifier of a shared memory segment.
Otherwise, -1 is returned and
set to indicate the error.
will fail if:
Bq Er 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.
Bq Er ENOENT
No shared memory segment was found matching
Fa key ,
and IPC_CREAT was not specified.
Bq Er ENOSPC
The kernel was unable to allocate enough memory to
satisfy the request.
Bq Er EEXIST
IPC_CREAT and IPC_EXCL were specified, and a shared memory segment