shm_open(3C)						   Standard C Library Functions 					      shm_open(3C)

NAME

       shm_open - open a shared memory object

SYNOPSIS

       #include <sys/mman.h>

       int shm_open(const char *name, int oflag, mode_t mode);

DESCRIPTION

       The  shm_open() function establishes a connection between a shared memory object and a file descriptor. It creates an open file description
       that refers to the shared memory object and a file descriptor that refers to that open file description. The file  descriptor  is  used	by
       other  functions  to refer to that shared memory object. The name argument points to a string naming a shared memory object. It is unspeci-
       fied whether the name appears in the file system and is visible to other functions that take pathnames as arguments. The name argument con-
       forms to the construction rules for a pathname. The first character of  name must be a slash  (/) character and the remaining characters of
       name cannot include any slash characters.  For maximum portability,  name should include no more than 14 characters, but this limit is  not
       enforced.

       If  successful, shm_open() returns a file descriptor for the shared memory object that is the lowest numbered file descriptor not currently
       open for that process. The open file description is new, and therefore the file descriptor does not share it with any other  processes.	It
       is unspecified whether the file offset is set. The FD_CLOEXEC file descriptor flag associated with the new file descriptor is set.

       The  file  status  flags  and file access modes of the open file description are according to the value of oflag. The oflag argument is the
       bitwise inclusive OR of the following flags defined in the header <fcntl.h>. Applications specify exactly  one  of  the	first  two  values
       (access modes) below in the value of oflag:

       O_RDONLY     Open for read access only.

       O_RDWR	    Open for read or write access.

       Any combination of the remaining flags may be specified in the value of oflag:

       O_CREAT	   If  the  shared  memory object exists, this flag has no effect, except as noted under O_EXCL below. Otherwise the shared memory
		   object is created; the user ID of the shared memory object will be set to the effective user ID of the process; the group ID of
		   the	shared	memory object will be set to a system default group ID or to the effective group ID of the process. The permission
		   bits of the shared memory object will be set to the value of the mode argument except those set in the file mode creation  mask
		   of  the  process.  When  bits in mode other than the file permission bits are set, the effect is unspecified. The mode argument
		   does not affect whether the shared memory object is opened for reading, for writing, or for both. The shared memory object  has
		   a size of zero.

       O_EXCL	   If  O_EXCL  and O_CREAT are set, shm_open() fails if the shared memory object exists. The check for the existence of the shared
		   memory object and the creation of the object if it does  not  exist	is  atomic  with  respect  to  other  processes  executing
		   shm_open()  naming  the  same  shared  memory  object with O_EXCL and O_CREAT set. If O_EXCL is set and O_CREAT is not set, the
		   result is undefined.

       O_TRUNC	   If the shared memory object exists, and it is successfully opened O_RDWR, the object will be truncated to zero length  and  the
		   mode and owner will be unchanged by this function call. The result of using O_TRUNC with O_RDONLY is undefined.

       When a shared memory object is created, the state of the shared memory object, including all data associated with the shared memory object,
       persists until the shared memory object is unlinked and all other references are gone. It is unspecified whether the name and shared memory
       object state remain valid after a system reboot.

RETURN VALUES

       Upon successful completion, the shm_open() function returns a non-negative integer representing the lowest numbered unused file descriptor.
       Otherwise, it returns -1 and sets errno to indicate the error condition.

ERRORS

       The shm_open() function will fail if:

       EACCES		The shared memory object exists and the permissions specified by oflag are denied, or the shared memory  object  does  not
			exist and permission to create the shared memory object is denied, or O_TRUNC is specified and write permission is denied.

       EEXIST		O_CREAT and O_EXCL are set and the named shared memory object already exists.

       EINTR		The shm_open() operation was interrupted by a signal.

       EINVAL		The shm_open() operation is not supported for the given name.

       EMFILE		Too many file descriptors are currently in use by this process.

       ENAMETOOLONG	The  length  of the name string exceeds PATH_MAX, or a pathname component is longer than NAME_MAX while _POSIX_NO_TRUNC is
			in effect.

       ENFILE		Too many shared memory objects are currently open in the system.

       ENOENT		O_CREAT is not set and the named shared memory object does not exist.

       ENOSPC		There is insufficient space for the creation of the new shared memory object.

       ENOSYS		The shm_open() function is not supported by the system.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |ATTRIBUTE TYPE		     |ATTRIBUTE VALUE		   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Committed 		   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+
       |Standard		     |See standards(5). 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       close(2), dup(2), exec(2), fcntl(2), mmap(2), umask(2), shm_unlink(3C), sysconf(3C), fcntl.h(3HEAD), attributes(5), standards(5)

NOTES

       Solaris 2.6 was the first release to support the Asynchronous Input and Output option. Prior to this release, this function always returned
       -1 and set errno to ENOSYS.

SunOS 5.11							    5 Feb 2008							      shm_open(3C)