186 lines
4.9 KiB
Groff
186 lines
4.9 KiB
Groff
.\" Copyright (c) 1980 Regents of the University of California.
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.\" All rights reserved. The Berkeley software License Agreement
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.\" specifies the terms and conditions for redistribution.
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.\"
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.\" @(#)open.2 6.4 (Berkeley) 5/14/86
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.\"
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.TH OPEN 2 "May 14, 1986"
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.UC 4
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.SH NAME
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open \- open a file for reading or writing, or create a new file
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.SH SYNOPSIS
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.nf
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.ft B
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#include <sys/types.h>
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#include <fcntl.h>
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int open(const char *\fIpath\fP, int \fIflags\fP \fR[\fP, mode_t \fImode\fP\fR]\fP)
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.ft R
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.fi
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.SH DESCRIPTION
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.B Open
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opens the file
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.I path
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for reading and/or writing, as specified by the
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.I flags
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argument and returns a descriptor for that file.
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The
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.I flags
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argument may indicate the file is to be
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created if it does not already exist (by specifying the
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O_CREAT flag), in which case the file is created with mode
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.I mode
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as described in
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.BR chmod (2)
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and modified by the process' umask value (see
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.BR umask (2)).
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.PP
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.I Path
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is the address of a string of ASCII characters representing
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a path name, terminated by a null character.
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The flags specified are formed by
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.IR or 'ing
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the following values
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.PP
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.RS
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.ta +12n
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.nf
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O_RDONLY open for reading only
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O_WRONLY open for writing only
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O_RDWR open for reading and writing
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O_NONBLOCK do not block on open
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O_APPEND append on each write
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O_CREAT create file if it does not exist
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O_TRUNC truncate size to 0
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O_EXCL error if create and file exists
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.fi
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.DT
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.RE
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.PP
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Opening a file with O_APPEND set causes each write on the file
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to be appended to the end. If O_TRUNC is specified and the
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file exists, the file is truncated to zero length.
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If O_EXCL is set with O_CREAT, then if the file already
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exists, the open returns an error. This can be used to
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implement a simple exclusive access locking mechanism.
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If O_EXCL is set and the last component of the pathname is
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a symbolic link, the open will fail even if the symbolic
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link points to a non-existent name.
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If the O_NONBLOCK flag is specified and the open call would result
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in the process being blocked for some reason, the open returns immediately.
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.PP
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Upon successful completion a non-negative integer termed a
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file descriptor is returned.
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The file pointer used to mark the current position within the
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file is set to the beginning of the file.
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.PP
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The new descriptor is set to remain open across
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.BR execve
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system calls; see
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.BR close (2).
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.PP
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The system imposes a limit on the number of descriptors
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open simultaneously by one process.
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.SH "ERRORS
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The named file is opened unless one or more of the
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following are true:
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.TP 15
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[ENOTDIR]
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A component of the path prefix is not a directory.
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.TP 15
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[ENAMETOOLONG]
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The path name exceeds PATH_MAX characters.
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.TP 15
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[ENOENT]
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O_CREAT is not set and the named file does not exist.
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.TP 15
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[ENOENT]
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A component of the path name that must exist does not exist.
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.TP 15
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[EACCES]
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Search permission is denied for a component of the path prefix.
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.TP 15
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[EACCES]
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The required permissions (for reading and/or writing)
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are denied for the named file.
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.TP 15
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[EACCES]
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O_CREAT 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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.TP 15
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[EACCES]
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A device to be opened for writing is physically write protected.
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.TP 15
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[ELOOP]
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Too many symbolic links were encountered in translating the pathname.
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(Minix-vmd)
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.TP 15
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[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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.TP 15
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[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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.TP 15
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[EMFILE]
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The system limit for open file descriptors per process has already been reached.
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.TP 15
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[ENFILE]
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The system file table is full.
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.TP 15
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[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.
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.TP 15
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[ENOSPC]
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O_CREAT 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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.TP 15
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[ENOSPC]
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O_CREAT 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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.ig
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.TP 15
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[EDQUOT]
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O_CREAT 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 fie
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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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.TP 15
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[EDQUOT]
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O_CREAT 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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..
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.TP 15
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[EIO]
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An I/O error occurred while making the directory entry or
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allocating the inode for O_CREAT.
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.TP 15
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[EFAULT]
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.I Path
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points outside the process's allocated address space.
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.TP 15
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[EEXIST]
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O_CREAT and O_EXCL were specified and the file exists.
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.SH "SEE ALSO"
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.BR chmod (2),
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.BR close (2),
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.BR dup (2),
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.BR fcntl (2),
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.BR lseek (2),
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.BR read (2),
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.BR write (2),
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.BR umask (2).
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