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readlink.2: Merge text of readlinkat(2)
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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man2/readlink.2
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man2/readlink.2
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@ -1,5 +1,6 @@
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.\" Copyright (c) 1983, 1991 The Regents of the University of California.
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.\" And Copyright (C) 2011 Guillem Jover <guillem@hadrons.org>
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.\" And Copyright (C) 2006, 2014 Michael Kerrisk
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.\" All rights reserved.
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.\"
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.\" %%%LICENSE_START(BSD_4_CLAUSE_UCB)
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@ -40,14 +41,22 @@
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.\" 2011-09-20, Guillem Jover <guillem@hadrons.org>:
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.\" Added text on dynamically allocating buffer + example program
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.\"
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.TH READLINK 2 2013-10-26 "Linux" "Linux Programmer's Manual"
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.TH READLINK 2 2014-02-21 "Linux" "Linux Programmer's Manual"
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.SH NAME
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readlink \- read value of a symbolic link
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readlink, readlinkat \- read value of a symbolic link
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.SH SYNOPSIS
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.nf
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.B #include <unistd.h>
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.sp
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.BI "ssize_t readlink(const char *" path ", char *" buf ", size_t " bufsiz );
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.sp
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.BR "#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 readlinkat(int " dirfd ", const char *" pathname ,
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.BI " char *" buf ", size_t " bufsiz );
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.sp
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.fi
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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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@ -59,7 +68,20 @@ Feature Test Macro Requirements for glibc (see
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_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
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_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED || _POSIX_C_SOURCE\ >=\ 200112L
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.RE
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.sp
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.BR readlinkat ():
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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 b
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.PD
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.SH DESCRIPTION
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.BR readlink ()
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places the contents of the symbolic link
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@ -74,10 +96,61 @@ does not append a null byte to
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It will truncate the contents (to a length of
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.I bufsiz
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characters), in case the buffer is too small to hold all of the contents.
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.SS readlinkat()
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The
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.BR readlinkat ()
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system call operates in exactly the same way as
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.BR readlink (2),
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except for the differences described here.
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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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.I 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 readlink (2)
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for a relative pathname).
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If
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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
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.I pathname
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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 readlink (2)).
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If
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.I pathname
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is absolute, then
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.I dirfd
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is ignored.
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Since Linux 2.6.39,
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.\" commit 65cfc6722361570bfe255698d9cd4dccaf47570d
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.I pathname
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can be an empty string,
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in which case the call operates on the file referred to by
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.IR dirfd
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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 dirfd
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can refer to any type of file, not just a directory.
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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 readlinkat ().
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.SH RETURN VALUE
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On success,
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.BR readlink ()
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returns the number of bytes placed in
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On success, these calls return the number of bytes placed in
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.IR buf .
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On error, \-1 is returned and
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.I errno
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@ -122,11 +195,32 @@ Insufficient kernel memory was available.
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.TP
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.B ENOTDIR
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A component of the path prefix is not a directory.
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.PP
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The following additional errors can occur for
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.BR readlinkat ():
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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 pathname
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is relative and
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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 VERSIONS
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.BR readlinkat ()
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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 readlink ():
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4.4BSD
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.RB ( readlink ()
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first appeared in 4.2BSD),
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POSIX.1-2001.
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.BR readlinkat ():
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POSIX.1-2008.
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.SH NOTES
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In versions of glibc up to and including glibc 2.4, the return type of
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.BR readlink ()
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@ -214,7 +308,6 @@ main(int argc, char *argv[])
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.SH SEE ALSO
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.BR readlink (1),
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.BR lstat (2),
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.BR readlinkat (2),
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.BR stat (2),
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.BR symlink (2),
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.BR path_resolution (7),
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