


      OPEN(2)                     (UNIX 5.0)                    OPEN(2)



      NAME
           open - open for reading or writing

      SYNTAX
           #include <fcntl.h>
           int open (path, oflag [ , mode ] )
           char *path;
           int oflag, mode;

      DESCRIPTION
           Path points to a path name naming a file.  Open opens a file
           descriptor for the named file and sets the file status flags
           according to the value of oflag.  Oflag values are
           constructed by or-ing flags from the following list (only
           one of the first three flags below may be used):

           O_RDONLY Open for reading only.

           O_WRONLY Open for writing only.

           O_RDWR   Open for reading and writing.

           O_NDELAY This flag may affect subsequent reads and writes.
                    See read(2) and write(2).

                    When opening a FIFO with O_RDONLY or O_WRONLY set:

                    If O_NDELAY is set:

                         An open for reading-only will return without
                         delay.  An open for writing-only will return
                         an error if no process currently has the file
                         open for reading.

                    If O_NDELAY is clear:

                         An open for reading-only will block until a
                         process opens the file for writing.  An open
                         for writing-only will block until a process
                         opens the file for reading.

                    When opening a file associated with a communication
                    line:

                    If O_NDELAY is set:

                         The open will return without waiting for
                         carrier.

                    If O_NDELAY is clear:

                         The open will block until carrier is present.



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      OPEN(2)                     (UNIX 5.0)                    OPEN(2)



           O_APPEND If set, the file pointer will be set to the end of
                    the file prior to each write.

           O_CREAT  If the file exists, this flag has no effect.
                    Otherwise, the file's owner ID is set to the
                    process's effective user ID, the file's group ID is
                    set to the process's effective group ID, and the
                    low-order 12 bits of the file mode are set to the
                    value of mode modified as follows (see creat(2)):

                         All bits set in the process's file mode
                         creation mask are cleared.  See umask(2).

                         The ``save text image after execution bit'' of
                         the mode is cleared.  See chmod(2).

           O_TRUNC  If the file exists, its length is truncated to 0
                    and the mode and owner are unchanged.

           O_EXCL   If O_EXCL and O_CREAT are set, open will fail if
                    the file exists.

           Upon successful completion a non-negative integer, the file
           descriptor, is returned.

           The file pointer used to mark the current position within
           the file is set to the beginning of the file.

           The new file descriptor is set to remain open across exec
           system calls.  See fcntl(2).

           No process may have more than 64 file descriptors open
           simultaneously.

           The named file is opened unless one or more of the following
           are true:

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

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

                A component of the path prefix denies search
                permission.  [EACCES]

                Oflag permission is denied for the named file.
                [EACCES]

                The named file is a directory and oflag is write or
                read/write.  [EISDIR]




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      OPEN(2)                     (UNIX 5.0)                    OPEN(2)



                The named file resides on a read-only file system and
                oflag is write or read/write.  [EROFS]

                Sixty-four (64) file descriptors are currently open.
                [EMFILE]

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

                The file is a pure procedure (shared text) file that is
                being executed and oflag is write or read/write.
                [ETXTBSY]

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

                O_CREAT and O_EXCL are set, and the named file exists.
                [EEXIST]

                O_NDELAY is set, the named file is a FIFO, O_WRONLY is
                set, and no process has the file open for reading.
                [ENXIO]

                The file exists, mandatory file/record locking is set,
                and there are outstanding record locks on the file (see
                chmod(2)).  [EAGAIN]

      RETURN VALUE
           Upon successful completion, a non-negative integer, namely a
           file descriptor, is returned.  Otherwise, a value of -1 is
           returned and errno is set to indicate the error.

      SEE ALSO
           chmod(2), close(2), creat(2), dup(2), fcntl(2), lseek(2),
           read(2), write(2).



















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