.\" Copyright (c) 1980, 1991 Regents of the University of California.
.\" %sccs.include.redist.man%
.\" @(#)open.2 6.8 (Berkeley) %G%
.Nd open or create a file for reading or writing
.Fd #include <sys/file.h>
.Fn open "const char *path" "int flags" "mode_t mode"
The file name specified by
for reading and/or writing as specified by the
and the file descriptor returned to the calling process.
argument may indicate the file is to be
created if it does not exist (by specifying the
flag), in which case the file is created with mode
and modified by the process' umask value (see
The flags specified are formed by
.Bd -literal -offset indent -compact
O_RDONLY open for reading only
O_WRONLY open for writing only
O_RDWR open for reading and writing
O_NDELAY 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
set causes each write on the file
to be appended to the end. If
file exists, the file is truncated to zero length.
returns an error. This may be used to
implement a simple exclusive access locking mechanism.
is set and the last component of the pathname is
will fail even if the symbolic
link points to a non-existent name.
flag is specified and the
in the process being blocked for some reason (e.g., waiting for
carrier on a dialup line),
The first time the process attempts to perform I/O on the open
file it will block (not currently implemented).
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.
The new descriptor is set to remain open across
The system imposes a limit on the number of file descriptors
open simultaneously by one process.
returns the current system limit.
The named file is opened unless:
A component of the path prefix is not a directory.
The pathname contains a character with the high-order bit set.
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
is not set and the named file does not exist.
A component of the path name that must exist does not exist.
Search permission is denied for a component of the path prefix.
The required permissions (for reading and/or writing)
are denied for the given flags.
and the directory in which it is to be created
Too many symbolic links were encountered in translating the pathname.
The named file is a directory, and the arguments specify
it is to be opened for writing.
The named file resides on a read-only file system,
and the file is to be modified.
The process has already reached its limit for open file descriptors.
The system file table is full.
The named file is a character special or block
special file, and the device associated with this special file
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.
and there are no free inodes on the file system on which the
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.
and the user's quota of inodes on the file system on
which the file is being created has been exhausted.
An I/O error occurred while making the directory entry or
The file is a pure procedure (shared text) file that is being
call requests write access.
points outside the process's allocated address space.
were specified and the file exists.
An attempt was made to open a socket (not currently implemented).
function call appeared in Version 6 AT&T UNIX.
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