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openat(2) is new in 2.6.16.
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.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" This manpage is Copyright (C) 2006, Michael Kerrisk
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\"
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.TH OPENAT 2 2006-03-06 "Linux 2.6.16" "Linux Programmer's Manual"
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.SH NAME
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openat \- open a file at a relative location
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.SH SYNOPSIS
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.nf
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.B #include <sys/types.h>
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.B #include <sys/stat.h>
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.B #include <fcntl.h>
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.sp
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.BI "int openat(int " dirfd ", const char *" pathname ", int " flags );
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.BI "int openat(int " dirfd ", const char *" pathname ", int " flags \
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", mode_t " mode );
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.fi
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.SH DESCRIPTION
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The
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.BR openat ()
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system call operates in exactly the same way as
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.BR open (2),
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except for the differences described in this manual page.
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If the pathname given in
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.I pathname
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is relative, then it is interpreted relative to the directory
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referred to by the file descriptor
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.IR dirfd
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(rather than relative to the current working directory of
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the calling process, as is done by
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.BR open (2)
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for a relative pathname).
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If the pathname given in
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.I pathname
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is relative and
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.I dirfd
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is the special value
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.BR AT_FDCWD ,
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then pathname is interpreted relative to the current working
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directory of the calling process (like
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.BR open (2)).
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If the pathname given in
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.IR pathname
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is absolute, then
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.I dirfd
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is ignored.
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.SH "RETURN VALUE"
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.BR openat ()
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returns a new file descriptor, or \-1 if an error occurred
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(in which case,
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.I errno
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is set appropriately).
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.SH ERRORS
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The same errors that occur for
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.BR open (2)
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can also occur for
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.BR openat (2).
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The following additional errors can occur for
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.BR openat ():
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.TP
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.B EBADF
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.I dirfd
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is not a valid file descriptor.
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.TP
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.B ENOTDIR
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.I dirfd
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is a file descriptor referring to a file other than a directory.
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.SH NOTES
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The
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.BR openat ()
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system call (and similar system calls suffixed "at")
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provides functionality that can otherwise only be obtained
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less efficiently or at the risk of races in user applications.
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It allows the implementation of a per-thread "current working
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directory", via file descriptor(s) maintained by the application.
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(This functionality can also be obtained by tricks based
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on the use of
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.IR /proc/self/fd/ dirfd,
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but less efficiently.)
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It also allows the avoidance of various kinds of races that can occur
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as a result of directory deletions that may occur while an application
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is traversing a file system.
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.SH "CONFORMING TO"
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This system call is non-standard.
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A similar system call exists on Solaris.
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.\" The 'at' suffix in Solaris is actually double sensed. It
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.\" primarily referred to "extended *at*tributes", which are
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.\" handled by Solaris' O_XATTR flag, but was also intended
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.\" to refer to the notion of "at a relative location".
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.SH VERSIONS
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.BR openat ()
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was added to Linux in kernel 2.6.16.
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.SH "SEE ALSO"
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.BR open (2),
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.BR path_resolution (2)
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.\" FIXME add SEE ALSO for openat() to open.2
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@ -158,4 +158,5 @@ EINTR, ELOOP, EMULTIHOP, ENAMETOOLONG, ENOLINK, ENOLINK, ENOTDIR.
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4.3BSD
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.SH "SEE ALSO"
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.BR chattr (1),
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.BR stat (2)
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.BR stat (2),
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.BR futimes (3)
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