1SYMLINK(3P) POSIX Programmer's Manual SYMLINK(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 symlink, symlinkat — make a symbolic link
13
15 #include <unistd.h>
16 int symlink(const char *path1, const char *path2);
18 #include <fcntl.h>
20 int symlinkat(const char *path1, int fd, const char *path2);
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24 The symlink() function shall create a symbolic link called path2 that
25 contains the string pointed to by path1 (path2 is the name of the sym‐
26 bolic link created, path1 is the string contained in the symbolic
27 link).
28 The string pointed to by path1 shall be treated only as a string and
30 shall not be validated as a pathname.
31 If the symlink() function fails for any reason other than [EIO], any
33 file named by path2 shall be unaffected.
34 If path2 names a symbolic link, symlink() shall fail and set errno to
36 [EEXIST].
37 The symbolic link's user ID shall be set to the process' effective user
39 ID. The symbolic link's group ID shall be set to the group ID of the
40 parent directory or to the effective group ID of the process. Implemen‐
41 tations shall provide a way to initialize the symbolic link's group ID
42 to the group ID of the parent directory. Implementations may, but need
43 not, provide an implementation-defined way to initialize the symbolic
44 link's group ID to the effective group ID of the calling process.
45 The values of the file mode bits for the created symbolic link are
47 unspecified. All interfaces specified by POSIX.1‐2008 shall behave as
48 if the contents of symbolic links can always be read, except that the
49 value of the file mode bits returned in the st_mode field of the stat
50 structure is unspecified.
51 Upon successful completion, symlink() shall mark for update the last
53 data access, last data modification, and last file status change time‐
54 stamps of the symbolic link. Also, the last data modification and last
55 file status change timestamps of the directory that contains the new
56 entry shall be marked for update.
57 The symlinkat() function shall be equivalent to the symlink() function
59 except in the case where path2 specifies a relative path. In this case
60 the symbolic link is created relative to the directory associated with
61 the file descriptor fd instead of the current working directory. If the
62 access mode of the open file description associated with the file
63 descriptor is not O_SEARCH, the function shall check whether directory
64 searches are permitted using the current permissions of the directory
65 underlying the file descriptor. If the access mode is O_SEARCH, the
66 function shall not perform the check.
67 If symlinkat() is passed the special value AT_FDCWD in the fd parame‐
69 ter, the current working directory shall be used and the behavior shall
70 be identical to a call to symlink().
71
73 Upon successful completion, these functions shall return 0. Otherwise,
74 these functions shall return -1 and set errno to indicate the error.
75
77 These functions shall fail if:
78 EACCES Write permission is denied in the directory where the symbolic
80 link is being created, or search permission is denied for a com‐
81 ponent of the path prefix of path2.
82 EEXIST The path2 argument names an existing file.
84 EIO An I/O error occurs while reading from or writing to the file
86 system.
87 ELOOP A loop exists in symbolic links encountered during resolution of
89 the path2 argument.
90 ENAMETOOLONG
92 The length of a component of the pathname specified by the path2
93 argument is longer than {NAME_MAX} or the length of the path1
94 argument is longer than {SYMLINK_MAX}.
95 ENOENT A component of the path prefix of path2 does not name an exist‐
97 ing file or path2 is an empty string.
98 ENOENT or ENOTDIR
100 The path2 argument contains at least one non-<slash> character
101 and ends with one or more trailing <slash> characters. If path2
102 without the trailing <slash> characters would name an existing
103 file, an [ENOENT] error shall not occur.
104 ENOSPC The directory in which the entry for the new symbolic link is
106 being placed cannot be extended because no space is left on the
107 file system containing the directory, or the new symbolic link
108 cannot be created because no space is left on the file system
109 which shall contain the link, or the file system is out of file-
110 allocation resources.
111 ENOTDIR
113 A component of the path prefix of path2 names an existing file
114 that is neither a directory nor a symbolic link to a directory.
115 EROFS The new symbolic link would reside on a read-only file system.
117 The symlinkat() function shall fail if:
119 EACCES The access mode of the open file description associated with fd
121 is not O_SEARCH and the permissions of the directory underlying
122 fd do not permit directory searches.
123 EBADF The path2 argument does not specify an absolute path and the fd
125 argument is neither AT_FDCWD nor a valid file descriptor open
126 for reading or searching.
127 ENOTDIR
129 The path2 argument is not an absolute path and fd is a file
130 descriptor associated with a non-directory file.
131 These functions may fail if:
133 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
135 resolution of the path2 argument.
136 ENAMETOOLONG
138 The length of the path2 argument exceeds {PATH_MAX} or pathname
139 resolution of a symbolic link in the path2 argument produced an
140 intermediate result with a length that exceeds {PATH_MAX}.
141 The following sections are informative.
143
145 None.
146
148 Like a hard link, a symbolic link allows a file to have multiple logi‐
149 cal names. The presence of a hard link guarantees the existence of a
150 file, even after the original name has been removed. A symbolic link
151 provides no such assurance; in fact, the file named by the path1 argu‐
152 ment need not exist when the link is created. A symbolic link can cross
153 file system boundaries.
154 Normal permission checks are made on each component of the symbolic
156 link pathname during its resolution.
157
159 The purpose of the symlinkat() function is to create symbolic links in
160 directories other than the current working directory without exposure
161 to race conditions. Any part of the path of a file could be changed in
162 parallel to a call to symlink(), resulting in unspecified behavior. By
163 opening a file descriptor for the target directory and using the sym‐
164 linkat() function it can be guaranteed that the created symbolic link
165 is located relative to the desired directory.
166
168 None.
169
171 fdopendir(), fstatat(), lchown(), link(), open(), readlink(), rename(),
172 unlink()
173 The Base Definitions volume of POSIX.1‐2017, <fcntl.h>, <unistd.h>
175
177 Portions of this text are reprinted and reproduced in electronic form
178 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
179 table Operating System Interface (POSIX), The Open Group Base Specifi‐
180 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
181 Electrical and Electronics Engineers, Inc and The Open Group. In the
182 event of any discrepancy between this version and the original IEEE and
183 The Open Group Standard, the original IEEE and The Open Group Standard
184 is the referee document. The original Standard can be obtained online
185 at http://www.opengroup.org/unix/online.html .
186 Any typographical or formatting errors that appear in this page are
188 most likely to have been introduced during the conversion of the source
189 files to man page format. To report such errors, see https://www.ker‐
190 nel.org/doc/man-pages/reporting_bugs.html .
191IEEE/The Open Group 2017 SYMLINK(3P)