mirror of https://github.com/mkerrisk/man-pages
277 lines
6.7 KiB
Groff
277 lines
6.7 KiB
Groff
.\" This manpage is Copyright (C) 1992 Drew Eckhardt;
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.\" and Copyright (C) 1993 Michael Haardt, Ian Jackson.
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.\" and Copyright (C) 2006, 2014 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.\" manual page may be incorrect or out-of-date.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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.\" Modified 1993-07-24 by Rik Faith
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.\" Modified 1996-04-26 by Nick Duffek <nsd@bbc.com>
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.\" Modified 1996-11-06 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.TH SYMLINK 2 2021-08-27 "Linux" "Linux Programmer's Manual"
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.SH NAME
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symlink, symlinkat \- make a new name for a file
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.SH SYNOPSIS
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.nf
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.B #include <unistd.h>
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.PP
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.BI "int symlink(const char *" target ", const char *" linkpath );
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.PP
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.BR "#include <fcntl.h> " "/* Definition of " AT_* " constants */"
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.B #include <unistd.h>
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.PP
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.BI "int symlinkat(const char *" target ", int " newdirfd \
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", const char *" linkpath );
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.PP
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.fi
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.RS -4
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.RE
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.PP
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.BR symlink ():
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.nf
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_XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200112L
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.\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
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|| /* Glibc <= 2.19: */ _BSD_SOURCE
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.fi
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.PP
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.BR symlinkat ():
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.nf
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Since glibc 2.10:
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_POSIX_C_SOURCE >= 200809L
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Before glibc 2.10:
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_ATFILE_SOURCE
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.fi
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.SH DESCRIPTION
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.BR symlink ()
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creates a symbolic link named
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.I linkpath
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which contains the string
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.IR target .
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.PP
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Symbolic links are interpreted at run time as if the contents of the
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link had been substituted into the path being followed to find a file or
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directory.
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.PP
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Symbolic links may contain
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.I ..
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path components, which (if used at the start of the link) refer to the
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parent directories of that in which the link resides.
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.PP
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A symbolic link (also known as a soft link) may point to an existing
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file or to a nonexistent one; the latter case is known as a dangling
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link.
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.PP
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The permissions of a symbolic link are irrelevant; the ownership is
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ignored when following the link, but is checked when removal or
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renaming of the link is requested and the link is in a directory with
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the sticky bit
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.RB ( S_ISVTX )
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set.
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.PP
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If
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.I linkpath
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exists, it will
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.I not
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be overwritten.
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.SS symlinkat()
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The
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.BR symlinkat ()
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system call operates in exactly the same way as
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.BR symlink (),
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except for the differences described here.
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.PP
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If the pathname given in
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.I linkpath
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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 newdirfd
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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 symlink ()
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for a relative pathname).
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.PP
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If
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.I linkpath
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is relative and
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.I newdirfd
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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 linkpath
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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 symlink ()).
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.PP
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If
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.I linkpath
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is absolute, then
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.I newdirfd
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is ignored.
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.PP
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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 symlinkat ().
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.SH RETURN VALUE
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On success, zero is returned.
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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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.TP
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.B EACCES
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Write access to the directory containing
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.I linkpath
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is denied, or one of the directories in the path prefix of
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.I linkpath
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did not allow search permission.
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(See also
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.BR path_resolution (7).)
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.TP
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.B EBADF
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.RB ( symlinkat ())
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.I linkpath
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is relative but
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.I newdirfd
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is neither
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.B AT_FDCWD
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nor a valid file descriptor.
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.TP
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.B EDQUOT
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The user's quota of resources on the filesystem has been exhausted.
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The resources could be inodes or disk blocks, depending on the filesystem
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implementation.
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.TP
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.B EEXIST
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.I linkpath
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already exists.
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.TP
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.B EFAULT
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.IR target " or " linkpath " points outside your accessible address space."
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.TP
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.B EIO
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An I/O error occurred.
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.TP
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.B ELOOP
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Too many symbolic links were encountered in resolving
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.IR linkpath .
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.TP
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.B ENAMETOOLONG
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.IR target " or " linkpath " was too long."
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.TP
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.B ENOENT
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A directory component in
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.I linkpath
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does not exist or is a dangling symbolic link, or
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.I target
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or
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.I linkpath
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is an empty string.
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.TP
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.B ENOENT
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.RB ( symlinkat ())
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.I linkpath
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is a relative pathname and
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.IR newdirfd
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refers to a directory that has been deleted.
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.TP
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.B ENOMEM
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Insufficient kernel memory was available.
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.TP
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.B ENOSPC
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The device containing the file has no room for the new directory
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entry.
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.TP
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.B ENOTDIR
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A component used as a directory in
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.I linkpath
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is not, in fact, a directory.
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.TP
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.B ENOTDIR
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.RB ( symlinkat ())
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.I linkpath
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is relative and
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.I newdirfd
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is a file descriptor referring to a file other than a directory.
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.TP
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.B EPERM
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The filesystem containing
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.I linkpath
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does not support the creation of symbolic links.
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.TP
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.B EROFS
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.I linkpath
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is on a read-only filesystem.
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.SH VERSIONS
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.BR symlinkat ()
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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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.BR symlink ():
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SVr4, 4.3BSD, POSIX.1-2001, POSIX.1-2008.
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.\" SVr4 documents additional error codes EDQUOT and ENOSYS.
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.\" See
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.\" .BR open (2)
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.\" re multiple files with the same name, and NFS.
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.PP
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.BR symlinkat ():
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POSIX.1-2008.
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.SH NOTES
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No checking of
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.I target
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is done.
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.PP
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Deleting the name referred to by a symbolic link will actually delete the
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file (unless it also has other hard links).
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If this behavior is not desired, use
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.BR link (2).
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.SS Glibc notes
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On older kernels where
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.BR symlinkat ()
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is unavailable, the glibc wrapper function falls back to the use of
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.BR symlink ().
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When
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.I linkpath
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is a relative pathname,
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glibc constructs a pathname based on the symbolic link in
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.IR /proc/self/fd
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that corresponds to the
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.IR newdirfd
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argument.
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.SH SEE ALSO
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.BR ln (1),
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.BR namei (1),
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.BR lchown (2),
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.BR link (2),
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.BR lstat (2),
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.BR open (2),
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.BR readlink (2),
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.BR rename (2),
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.BR unlink (2),
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.BR path_resolution (7),
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.BR symlink (7)
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