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OpenDarwin 7.2.1 - man page for open (opendarwin section 2)

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OPEN(2) 			     BSD System Calls Manual				  OPEN(2)

NAME
     open -- open or create a file for reading or writing

SYNOPSIS
     #include <fcntl.h>

     int
     open(const char *path, int flags, mode_t mode);

DESCRIPTION
     The file name specified by path is opened for reading and/or writing as specified by the
     argument flags and the file descriptor returned to the calling process.  The flags argument
     may indicate the file is to be created if it does not exist (by specifying the O_CREAT
     flag), in which case the file is created with mode mode as described in chmod(2) and modi-
     fied by the process' umask value (see umask(2)).

     The flags specified are formed by or'ing the following values

	   O_RDONLY	   open for reading only
	   O_WRONLY	   open for writing only
	   O_RDWR	   open for reading and writing
	   O_NONBLOCK	   do not block on open or for data to become available
	   O_APPEND	   append on each write
	   O_CREAT	   create file if it does not exist
	   O_TRUNC	   truncate size to 0
	   O_EXCL	   error if create and file exists
	   O_SHLOCK	   atomically obtain a shared lock
	   O_EXLOCK	   atomically obtain an exclusive lock

     Opening a file with O_APPEND set causes each write on the file to be appended to the end.
     If O_TRUNC is specified and the file exists, the file is truncated to zero length.  If
     O_EXCL is set with O_CREAT and the file already exists, open() returns an error.  This may
     be used to implement a simple exclusive access locking mechanism.	If O_EXCL is set and the
     last component of the pathname is a symbolic link, open() will fail even if the symbolic
     link points to a non-existent name.  If the O_NONBLOCK flag is specified, do not wait for
     the device or file to be ready or available.  If the open() call would result in the process
     being blocked for some reason (e.g., waiting for carrier on a dialup line), open() returns
     immediately.  This flag also has the effect of making all subsequent I/O on the open file
     non-blocking.

     When opening a file, a lock with flock(2) semantics can be obtained by setting O_SHLOCK for
     a shared lock, or O_EXLOCK for an exclusive lock.	If creating a file with O_CREAT, the
     request for the lock will never fail (provided that the underlying filesystem supports lock-
     ing).

     If successful, open() returns a non-negative integer, termed a file descriptor.  It returns
     -1 on failure.  The file pointer used to mark the current position within the file is set to
     the beginning of the file.

     When a new file is created it is given the group of the directory which contains it.

     The new descriptor is set to remain open across execve system calls; see close(2) and
     fcntl(2).

     The system imposes a limit on the number of file descriptors open simultaneously by one
     process.  Getdtablesize(2) returns the current system limit.

ERRORS
     The named file is opened unless:

     [ENOTDIR]		A component of the path prefix is not a directory.

     [ENAMETOOLONG]	A component of a pathname exceeded {NAME_MAX} characters, or an entire
			path name exceeded {PATH_MAX} characters.

     [ENOENT]		O_CREAT is not set and the named file does not exist.

     [ENOENT]		A component of the path name that must exist does not exist.

     [EACCES]		Search permission is denied for a component of the path prefix.

     [EACCES]		The required permissions (for reading and/or writing) are denied for the
			given flags.

     [EACCES]		O_CREAT is specified, the file does not exist, and the directory in which
			it is to be created does not permit writing.

     [ELOOP]		Too many symbolic links were encountered in translating the pathname.

     [EISDIR]		The named file is a directory, and the arguments specify it is to be
			opened for writing.

     [EROFS]		The named file resides on a read-only file system, and the file is to be
			modified.

     [EMFILE]		The process has already reached its limit for open file descriptors.

     [ENFILE]		The system file table is full.

     [ENXIO]		The named file is a character special or block special file, and the
			device associated with this special file does not exist.

     [EINTR]		The open() operation was interrupted by a signal.

     [EOPNOTSUPP]	O_SHLOCK or O_EXLOCK is specified but the underlying filesystem does not
			support locking.

     [ENOSPC]		O_CREAT is specified, the file does not exist, and the directory in which
			the entry for the new file is being placed cannot be extended because
			there is no space left on the file system containing the directory.

     [ENOSPC]		O_CREAT is specified, the file does not exist, and there are no free
			inodes on the file system on which the file is being created.

     [EDQUOT]		O_CREAT is specified, the file does not exist, and the directory in which
			the entry for the new file is being placed cannot be extended because the
			user's quota of disk blocks on the file system containing the directory
			has been exhausted.

     [EDQUOT]		O_CREAT is specified, the file does not exist, and the user's quota of
			inodes on the file system on which the file is being created has been
			exhausted.

     [EIO]		An I/O error occurred while making the directory entry or allocating the
			inode for O_CREAT.

     [ETXTBSY]		The file is a pure procedure (shared text) file that is being executed
			and the open() call requests write access.

     [EFAULT]		Path points outside the process's allocated address space.

     [EEXIST]		O_CREAT and O_EXCL were specified and the file exists.

     [EOPNOTSUPP]	An attempt was made to open a socket (not currently implemented).

SEE ALSO
     chmod(2), close(2), dup(2), getdtablesize(2), lseek(2), read(2), write(2), umask(2)

HISTORY
     An open() function call appeared in Version 6 AT&T UNIX.

4th Berkeley Distribution		November 16, 1993		4th Berkeley Distribution
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