338 lines
9.1 KiB
Groff
338 lines
9.1 KiB
Groff
.\" $NetBSD: open.2,v 1.32 2003/08/07 16:44:03 agc Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)open.2 8.2 (Berkeley) 11/16/93
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.\"
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.Dd May 8, 2003
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.Dt OPEN 2
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.Os
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.Sh NAME
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.Nm open
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.Nd open or create a file for reading or writing
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In fcntl.h
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.Ft int
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.Fn open "const char *path" "int flags" "mode_t mode"
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.Sh DESCRIPTION
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The file name specified by
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.Fa path
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is opened
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for reading and/or writing as specified by the
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argument
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.Fa flags
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and the file descriptor returned to the calling process.
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The
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.Fa flags
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are specified by
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.Em or Ns 'ing
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the following values.
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Applications must specify exactly one of the first three values
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(file access modes):
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.Bl -tag -offset indent -width O_NONBLOCK
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.It Dv O_RDONLY
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Open for reading only.
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.It Dv O_WRONLY
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Open for writing only.
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.It Dv O_RDWR
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Open for reading and writing.
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.El
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.Pp
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Any combination of the following may be used:
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.Bl -tag -offset indent -width O_NONBLOCK
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.It Dv O_NONBLOCK
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Do not block on open or for data to become available.
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.It Dv O_APPEND
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Append to the file on each write.
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.It Dv O_CREAT
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Create the file if it does not exist, in which case the file is
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created with mode
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.Ar mode
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as described in
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.Xr chmod 2
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and modified by the process' umask value (see
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.Xr umask 2 ) .
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.It Dv O_TRUNC
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Truncate size to 0.
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.It Dv O_EXCL
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Error if
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.Dv O_CREAT
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and the file already exists.
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.It Dv O_SHLOCK
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Atomically obtain a shared lock.
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.It Dv O_EXLOCK
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Atomically obtain an exclusive lock.
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.It Dv O_NOFOLLOW
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If last path element is a symlink, don't follow it. This option is
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provided for compatibility with other operating systems, but its
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security value is questionable.
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.It Dv O_DSYNC
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If set, write operations will be performed according to synchronized
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I/O data integrity completion:
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each write will wait for the file data to be committed to stable
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storage.
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.It Dv O_SYNC
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If set, write operations will be performed according to synchronized
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I/O file integrity completion:
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each write will wait for both the file data and file status to be
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committed to stable storage.
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.It Dv O_RSYNC
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If set, read operations will complete at the same level of
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integrity which is in effect for write operations:
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if specified together with
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.Dv O_SYNC ,
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each read will wait for the file status to be committed to stable
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storage.
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.Pp
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Combining
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.Dv O_RSYNC
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with
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.Dv O_DSYNC
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only, or specifying it without any other synchronized I/O integrity
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completion flag set, has no further effect.
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.El
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.Pp
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Opening a file with
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.Dv O_APPEND
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set causes each write on the file
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to be appended to the end.
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If
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.Dv O_TRUNC
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is specified and the
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file exists, the file is truncated to zero length.
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.Pp
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If
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.Dv O_EXCL
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is set with
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.Dv O_CREAT
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and the file already
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exists,
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.Fn open
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returns an error.
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This may be used to implement a simple exclusive access locking mechanism.
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If
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.Dv O_EXCL
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is set and the last component of the pathname is
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a symbolic link,
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.Fn open
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will fail even if the symbolic
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link points to a non-existent name.
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.Pp
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If the
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.Dv O_NONBLOCK
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flag is specified, do not wait for the device or file to be ready or
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available.
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If the
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.Fn open
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call would result
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in the process being blocked for some reason (e.g., waiting for
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carrier on a dialup line),
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.Fn open
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returns immediately.
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This flag also has the effect of making all subsequent I/O on the open file non-blocking.
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.Pp
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When opening a file, a lock with
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.Xr flock 2
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semantics can be obtained by setting
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.Dv O_SHLOCK
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for a shared lock, or
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.Dv O_EXLOCK
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for an exclusive lock.
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If creating a file with
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.Dv O_CREAT ,
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the request for the lock will never fail
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(provided that the underlying filesystem supports locking).
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.Pp
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If
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.Fn open
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is successful, the file pointer used to mark the current position within
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the file is set to the beginning of the file.
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.Pp
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When a new file is created it is given the group of the directory
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which contains it.
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.Pp
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The new descriptor is set to remain open across
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.Xr execve 2
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system calls; see
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.Xr close 2
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and
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.Xr fcntl 2 .
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.Pp
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The system imposes a limit on the number of file descriptors
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open simultaneously by one process.
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Calling
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.Xr getdtablesize 3
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returns the current system limit.
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.Sh RETURN VALUES
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If successful,
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.Fn open
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returns a non-negative integer, termed a file descriptor.
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Otherwise, a value of \-1 is returned and
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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The named file is opened unless:
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.Bl -tag -width Er
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.It Bq Er ENOTDIR
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A component of the path prefix is not a directory.
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.It Bq Er ENAMETOOLONG
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A component of a pathname exceeded
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.Dv {NAME_MAX}
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characters, or an entire path name exceeded
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.Dv {PATH_MAX}
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characters.
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.It Bq Er ENOENT
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.Dv O_CREAT
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is not set and the named file does not exist, or
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a component of the path name that must exist does not exist.
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.It Bq Er EACCES
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Search permission is denied for a component of the path prefix,
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the required permissions (for reading and/or writing)
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are denied for the given flags, or
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.Dv O_CREAT
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is specified,
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the file does not exist,
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and the directory in which it is to be created
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does not permit writing.
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.It Bq Er ELOOP
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Too many symbolic links were encountered in translating the pathname.
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.It Bq Er EISDIR
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The named file is a directory, and the arguments specify
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it is to be opened for writing.
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.It Bq Er EROFS
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The named file resides on a read-only file system,
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and the file is to be modified.
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.It Bq Er EMFILE
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The process has already reached its limit for open file descriptors.
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.It Bq Er ENFILE
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The system file table is full.
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.It Bq Er ENXIO
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The named file is a character special or block
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special file, and the device associated with this special file
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does not exist, or
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the named file is a
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.Tn FIFO ,
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.Dv O_NONBLOCK
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and
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.Dv O_WRONLY
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is set and no process has the file open for reading.
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.It Bq Er EINTR
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The
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.Fn open
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operation was interrupted by a signal.
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.It Bq Er EOPNOTSUPP
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.Dv O_SHLOCK
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or
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.Dv O_EXLOCK
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is specified but the underlying filesystem does not support locking.
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.It Bq Er ENOSPC
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.Dv O_CREAT
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is specified,
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the file does not exist,
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and the directory in which the entry for the new file is being placed
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cannot be extended because there is no space left on the file
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system containing the directory.
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.It Bq Er ENOSPC
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.Dv O_CREAT
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is specified,
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the file does not exist,
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and there are no free inodes on the file system on which the
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file is being created.
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.It Bq Er EDQUOT
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.Dv O_CREAT
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is specified,
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the file does not exist,
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and the directory in which the entry for the new file
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is being placed cannot be extended because the
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user's quota of disk blocks on the file system
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containing the directory has been exhausted.
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.It Bq Er EDQUOT
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.Dv O_CREAT
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is specified,
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the file does not exist,
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and the user's quota of inodes on the file system on
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which the file is being created has been exhausted.
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.It Bq Er EIO
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An I/O error occurred while making the directory entry or
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allocating the inode for
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.Dv O_CREAT .
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.It Bq Er ETXTBSY
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The file is a pure procedure (shared text) file that is being
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executed and the
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.Fn open
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call requests write access.
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.It Bq Er EFAULT
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.Fa path
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points outside the process's allocated address space.
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.It Bq Er EEXIST
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.Dv O_CREAT
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and
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.Dv O_EXCL
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were specified and the file exists.
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.It Bq Er EOPNOTSUPP
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An attempt was made to open a socket (not currently implemented).
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.El
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.Sh SEE ALSO
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.Xr chmod 2 ,
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.Xr close 2 ,
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.Xr dup 2 ,
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.Xr lseek 2 ,
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.Xr read 2 ,
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.Xr umask 2 ,
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.Xr write 2 ,
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.Xr getdtablesize 3
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.Sh STANDARDS
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The
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.Fn open
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function conforms to
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.St -p1003.1-90 .
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The
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.Fa flags
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values
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.Dv O_DSYNC ,
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.Dv O_SYNC
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and
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.Dv O_RSYNC
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are extensions defined in
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.St -p1003.1b-93 .
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.Pp
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The
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.Dv O_SHLOCK ,
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.Dv O_EXLOCK ,
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and
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.Dv O_NOFOLLOW
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flags are non-standard extensions and should not be used if portability
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is of concern.
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.Sh HISTORY
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An
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.Fn open
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function call appeared in
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.At v6 .
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