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linkat.2: Convert to link to link.2
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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man2/linkat.2
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man2/linkat.2
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.\" This manpage is Copyright (C) 2006, Michael Kerrisk
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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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.\" manual page may be incorrect or out-of-date.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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.\" %%%LICENSE_END
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.\"
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.TH LINKAT 2 2014-01-17 "Linux" "Linux Programmer's Manual"
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.SH NAME
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linkat \- create a file link relative to directory file descriptors
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.SH SYNOPSIS
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.nf
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.B #include <fcntl.h> /* Definition of AT_* constants */
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.B #include <unistd.h>
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.sp
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.BI "int linkat(int " olddirfd ", const char *" oldpath ,
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.BI " int " newdirfd ", const char *" newpath ", int " flags );
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.fi
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.BR linkat ():
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.PD 0
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.ad l
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.RS 4
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.TP 4
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Since glibc 2.10:
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_XOPEN_SOURCE\ >=\ 700 || _POSIX_C_SOURCE\ >=\ 200809L
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.TP
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Before glibc 2.10:
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_ATFILE_SOURCE
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.RE
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.ad
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.PD
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.SH DESCRIPTION
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The
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.BR linkat ()
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system call operates in exactly the same way as
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.BR link (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 oldpath
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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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.I olddirfd
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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 link (2)
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for a relative pathname).
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If
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.I oldpath
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is relative and
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.I olddirfd
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is the special value
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.BR AT_FDCWD ,
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then
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.I oldpath
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is interpreted relative to the current working
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directory of the calling process (like
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.BR link (2)).
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If
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.I oldpath
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is absolute, then
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.I olddirfd
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is ignored.
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The interpretation of
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.I newpath
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is as for
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.IR oldpath ,
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except that a relative pathname is interpreted relative
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to the directory referred to by the file descriptor
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.IR newdirfd .
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The following values can be bitwise ORed in
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.IR flags :
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.TP
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.BR AT_EMPTY_PATH " (since Linux 2.6.39)"
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.\" commit 11a7b371b64ef39fc5fb1b6f2218eef7c4d035e3
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If
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.I oldpath
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is an empty string, create a link to the file referenced by
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.IR olddirfd
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(which may have been obtained using the
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.BR open (2)
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.B O_PATH
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flag).
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In this case,
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.I olddirfd
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can refer to any type of file, not just a directory.
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The caller must have the
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.BR CAP_DAC_READ_SEARCH
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capability in order to use this flag;
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this prevents arbitrary users from creating hard links
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using file descriptors received via a UNIX domain socket
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(see the discussion of
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.BR SCM_RIGHTS
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in
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.BR unix (7)).
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This flag is Linux-specific; define
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.B _GNU_SOURCE
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.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
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to obtain its definition.
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.TP
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.BR AT_SYMLINK_FOLLOW " (since Linux 2.6.18)"
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By default,
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.BR linkat (),
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does not dereference
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.I oldpath
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if it is a symbolic link (like
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.BR link (2)).
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The flag
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.B AT_SYMLINK_FOLLOW
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can be specified in
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.I flags
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to cause
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.I oldpath
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to be dereferenced if it is a symbolic link.
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.PP
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Before kernel 2.6.18, the
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.I flags
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argument was unused, and had to be specified as 0.
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.SH RETURN VALUE
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On success,
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.BR linkat ()
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returns 0.
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On error, \-1 is returned and
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.I errno
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is set to indicate the error.
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.SH ERRORS
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The same errors that occur for
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.BR link (2)
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can also occur for
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.BR linkat ().
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The following additional errors can occur for
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.BR linkat ():
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.TP
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.B EBADF
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.I olddirfd
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or
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.I newdirfd
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is not a valid file descriptor.
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.TP
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.B EINVAL
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An invalid flag value was specified in
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.IR flags .
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.TP
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.B ENOENT
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.B AT_EMPTY_PATH
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was specified in
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.IR flags ,
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but the caller did not have the
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.B CAP_DAC_READ_SEARCH
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capability.
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.TP
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.B ENOENT
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An attempt was made to link to the
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.I /proc/self/fd/NN
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file corresponding to a file descriptor created with
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open(path, O_TMPFILE | O_EXCL, mode);
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See
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.BR open (2).
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.TP
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.B ENOTDIR
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.I oldpath
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is relative and
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.I olddirfd
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is a file descriptor referring to a file other than a directory;
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or similar for
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.I newpath
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and
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.I newdirfd
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.SH VERSIONS
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.BR linkat ()
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was added to Linux in kernel 2.6.16;
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library support was added to glibc in version 2.4.
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.SH CONFORMING TO
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POSIX.1-2008.
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.SH NOTES
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See
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.BR openat (2)
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for an explanation of the need for
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.BR linkat ().
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.SH SEE ALSO
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.BR link (2),
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.BR openat (2),
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.BR path_resolution (7),
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.BR symlink (7)
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.so man2/link.2
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