OPEN(2)             UNIX Programmer's Manual		  OPEN(2)


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

SYNOPSIS
     #include <fcntl.h>

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

DESCRIPTION
     Open opens the file path for reading and/or writing, as
     specified by the flags argument and returns a descriptor for
     that file.  The flags argument may indicate the file is to
     be created if it does not already exist (by specifying the
     O_CREAT flag), in which case the file is created with mode
     mode as described in chmod(2) and modified by the process'
     umask value (see umask(2)).

     Path is the address of a string of ASCII characters
     representing a path name, terminated by a null character.
     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
	   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_NOCTTY do not acquire as controlling terminal
	   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, then if the file already exists,
     the open returns an error.  This can 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,
     the open will fail even if the symbolic link points to a
     non-existent name.  If the O_NONBLOCK flag is specified and
     the open call would result in the process being blocked for
     some reason (e.g. waiting for carrier on a dialup line), the
     open returns immediately. The first time the process
     attempts to perform i/o on the open file it will block.


Printed 11/26/99	  Nov 30, 1994				1


OPEN(2)             UNIX Programmer's Manual		  OPEN(2)


     The flag O_NOCTTY indicates that even if the file is a ter-
     minal device, the call should not result in acquiring the
     terminal device as the controlling terminal of the caller.
     This flag is not the default and is currently unimplemented
     (it will be Real Soon Now).

     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.

     Upon successful completion a non-negative integer termed a
     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 descriptor is set to remain open across execve sys-
     tem calls; see close(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 one or more of the following
     are true:

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

     [EINVAL]	    The pathname contains a character with the
		    high-order bit set.

     [ENAMETOOLONG] A component of a pathname exceeded 255 char-
		    acters, or an entire path name exceeded 1023
		    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 named flag.

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


Printed 11/26/99	  Nov 30, 1994				2


OPEN(2)             UNIX Programmer's Manual		  OPEN(2)


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

     [EISDIR]	    The named file is a directory, and the argu-
		    ments specify it is to be opened for writ-
		    ting.

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

     [EMFILE]	    The system limit for open file descriptors
		    per process has already been reached.

     [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.

     [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 fie 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 direc-
		    tory 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.


Printed 11/26/99	  Nov 30, 1994				3


OPEN(2)             UNIX Programmer's Manual		  OPEN(2)


     [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)


Printed 11/26/99	  Nov 30, 1994				4


 
Generated: 2016-12-26
Generated by man2html V0.25
page hit count: 932
Valid CSS Valid XHTML 1.0 Strict