linkat(2)

1LINKAT(2)                  Linux Programmer's Manual                 LINKAT(2)
2
3
4

NAME

6       linkat - create a file link relative to directory file descriptors
7

SYNOPSIS

9       #include <fcntl.h> /* Definition of AT_* constants */
10       #include <unistd.h>
11
12       int linkat(int olddirfd, const char *oldpath,
13                  int newdirfd, const char *newpath, int flags);
14
15   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
16
17       linkat():
18           Since glibc 2.10:
19               _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
20           Before glibc 2.10:
21               _ATFILE_SOURCE
22

DESCRIPTION

24       The  linkat()  system call operates in exactly the same way as link(2),
25       except for the differences described in this manual page.
26
27       If the pathname given in oldpath is relative, then  it  is  interpreted
28       relative  to  the directory referred to by the file descriptor olddirfd
29       (rather than relative to the current working directory of  the  calling
30       process, as is done by link(2) for a relative pathname).
31
32       If oldpath is relative and olddirfd is the special value AT_FDCWD, then
33       oldpath is interpreted relative to the current working directory of the
34       calling process (like link(2)).
35
36       If oldpath is absolute, then olddirfd is ignored.
37
38       The interpretation of newpath is as for oldpath, except that a relative
39       pathname is interpreted relative to the directory referred  to  by  the
40       file descriptor newdirfd.
41
42       The following values can be biwise ORed in flags:
43
44       AT_EMPTY_PATH (since Linux 2.6.39)
45              If  oldpath is an empty string, create a link to the file refer‐
46              enced by olddirfd  (which  may  have  been  obtained  using  the
47              open(2)  O_PATH  flag).  In this case, olddirfd can refer to any
48              type of file, not just a directory.  The caller  must  have  the
49              CAP_DAC_READ_SEARCH  capability  in order to use this flag; this
50              prevents arbitrary users from creating  hard  links  using  file
51              descriptors  received  via a UNIX domain socket (see the discus‐
52              sion of SCM_RIGHTS in unix(7)).
53
54       AT_SYMLINK_FOLLOW (since Linux 2.6.18)
55              By default, linkat(), does not dereference oldpath if  it  is  a
56              symbolic link (like link(2)).  The flag AT_SYMLINK_FOLLOW can be
57              specified in flags to cause oldpath to be dereferenced if it  is
58              a symbolic link.
59
60       Before  kernel  2.6.18,  the  flags  argument was unused, and had to be
61       specified as 0.
62

RETURN VALUE

64       On success, linkat() returns 0.  On error, -1 is returned and errno  is
65       set to indicate the error.
66

ERRORS

68       The  same  errors  that  occur for link(2) can also occur for linkat().
69       The following additional errors can occur for linkat():
70
71       EBADF  olddirfd or newdirfd is not a valid file descriptor.
72
73       ENOENT AT_EMPTY_PATH was specified in flags, but  the  caller  did  not
74              have the CAP_DAC_READ_SEARCH capability.
75
76       ENOTDIR
77
78       ENOTDIR
79              oldpath  is relative and olddirfd is a file descriptor referring
80              to a file other than a directory; or  similar  for  newpath  and
81              newdirfd
82

VERSIONS

84       linkat() was added to Linux in kernel 2.6.16; library support was added
85       to glibc in version 2.4.
86

CONFORMING TO

88       POSIX.1-2008.
89

NOTES

91       See openat(2) for an explanation of the need for linkat().
92

COLOPHON

97       This page is part of release 3.53 of the Linux  man-pages  project.   A
98       description  of  the project, and information about reporting bugs, can
99       be found at http://www.kernel.org/doc/man-pages/.
100
101
102
103Linux                             2013-07-21                         LINKAT(2)