1FUTIMENS(3P) POSIX Programmer's Manual FUTIMENS(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 futimens, utimensat, utimes — set file access and modification times
13
15 #include <sys/stat.h>
16 int futimens(int fd, const struct timespec times[2]);
18 #include <fcntl.h>
20 int utimensat(int fd, const char *path, const struct timespec times[2],
22 int flag);
23 #include <sys/time.h>
25 int utimes(const char *path, const struct timeval times[2]);
27
29 The futimens() and utimensat() functions shall set the access and modi‐
30 fication times of a file to the values of the times argument. The futi‐
31 mens() function changes the times of the file associated with the file
32 descriptor fd. The utimensat() function changes the times of the file
33 pointed to by the path argument, relative to the directory associated
34 with the file descriptor fd. Both functions allow time specifications
35 accurate to the nanosecond.
36 For futimens() and utimensat(), the times argument is an array of two
38 timespec structures. The first array member represents the date and
39 time of last access, and the second member represents the date and time
40 of last modification. The times in the timespec structure are measured
41 in seconds and nanoseconds since the Epoch. The file's relevant time‐
42 stamp shall be set to the greatest value supported by the file system
43 that is not greater than the specified time.
44 If the tv_nsec field of a timespec structure has the special value
46 UTIME_NOW, the file's relevant timestamp shall be set to the greatest
47 value supported by the file system that is not greater than the current
48 time. If the tv_nsec field has the special value UTIME_OMIT, the file's
49 relevant timestamp shall not be changed. In either case, the tv_sec
50 field shall be ignored.
51 If the times argument is a null pointer, both the access and modifica‐
53 tion timestamps shall be set to the greatest value supported by the
54 file system that is not greater than the current time. If utimensat()
55 is passed a relative path in the path argument, the file to be used
56 shall be relative to the directory associated with the file descriptor
57 fd instead of the current working directory. If the access mode of the
58 open file description associated with the file descriptor is not
59 O_SEARCH, the function shall check whether directory searches are per‐
60 mitted using the current permissions of the directory underlying the
61 file descriptor. If the access mode is O_SEARCH, the function shall not
62 perform the check.
63 If utimensat() is passed the special value AT_FDCWD in the fd parame‐
65 ter, the current working directory shall be used.
66 Only a process with the effective user ID equal to the user ID of the
68 file, or with write access to the file, or with appropriate privileges
69 may use futimens() or utimensat() with a null pointer as the times
70 argument or with both tv_nsec fields set to the special value
71 UTIME_NOW. Only a process with the effective user ID equal to the user
72 ID of the file or with appropriate privileges may use futimens() or
73 utimensat() with a non-null times argument that does not have both
74 tv_nsec fields set to UTIME_NOW and does not have both tv_nsec fields
75 set to UTIME_OMIT. If both tv_nsec fields are set to UTIME_OMIT, no
76 ownership or permissions check shall be performed for the file, but
77 other error conditions may still be detected (including [EACCES] errors
78 related to the path prefix).
79 Values for the flag argument of utimensat() are constructed by a bit‐
81 wise-inclusive OR of flags from the following list, defined in
82 <fcntl.h>:
83 AT_SYMLINK_NOFOLLOW
85 If path names a symbolic link, then the access and modification
86 times of the symbolic link are changed.
87 Upon successful completion, futimens() and utimensat() shall mark the
89 last file status change timestamp for update, with the exception that
90 if both tv_nsec fields are set to UTIME_OMIT, the file status change
91 timestamp need not be marked for update.
92 The utimes() function shall be equivalent to the utimensat() function
94 with the special value AT_FDCWD as the fd argument and the flag argu‐
95 ment set to zero, except that the times argument is a timeval structure
96 rather than a timespec structure, and accuracy is only to the microsec‐
97 ond, not nanosecond, and rounding towards the nearest second may occur.
98
100 Upon successful completion, these functions shall return 0. Otherwise,
101 these functions shall return -1 and set errno to indicate the error. If
102 -1 is returned, the file times shall not be affected.
103
105 These functions shall fail if:
106 EACCES The times argument is a null pointer, or both tv_nsec values are
108 UTIME_NOW, and the effective user ID of the process does not
109 match the owner of the file and write access is denied.
110 EINVAL Either of the times argument structures specified a tv_nsec
112 value that was neither UTIME_NOW nor UTIME_OMIT, and was a value
113 less than zero or greater than or equal to 1000 million.
114 EINVAL A new file timestamp would be a value whose tv_sec component is
116 not a value supported by the file system.
117 EPERM The times argument is not a null pointer, does not have both
119 tv_nsec fields set to UTIME_NOW, does not have both tv_nsec
120 fields set to UTIME_OMIT, the calling process' effective user ID
121 does not match the owner of the file, and the calling process
122 does not have appropriate privileges.
123 EROFS The file system containing the file is read-only.
125 The futimens() function shall fail if:
127 EBADF The fd argument is not a valid file descriptor.
129 The utimensat() function shall fail if:
131 EACCES The access mode of the open file description associated with fd
133 is not O_SEARCH and the permissions of the directory underlying
134 fd do not permit directory searches.
135 EBADF The path argument does not specify an absolute path and the fd
137 argument is neither AT_FDCWD nor a valid file descriptor open
138 for reading or searching.
139 ENOTDIR
141 The path argument is not an absolute path and fd is a file
142 descriptor associated with a non-directory file.
143 The utimensat() and utimes() functions shall fail if:
145 EACCES Search permission is denied by a component of the path prefix.
147 ELOOP A loop exists in symbolic links encountered during resolution of
149 the path argument.
150 ENAMETOOLONG
152 The length of a component of a pathname is longer than
153 {NAME_MAX}.
154 ENOENT A component of path does not name an existing file or path is an
156 empty string.
157 ENOTDIR
159 A component of the path prefix names an existing file that is
160 neither a directory nor a symbolic link to a directory, or the
161 path argument contains at least one non-<slash> character and
162 ends with one or more trailing <slash> characters and the last
163 pathname component names an existing file that is neither a
164 directory nor a symbolic link to a directory.
165 The utimensat() and utimes() functions may fail if:
167 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
169 resolution of the path argument.
170 ENAMETOOLONG
172 The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
173 tion of a symbolic link produced an intermediate result with a
174 length that exceeds {PATH_MAX}.
175 The utimensat() function may fail if:
177 EINVAL The value of the flag argument is not valid.
179 The following sections are informative.
181
183 None.
184
186 None.
187
189 The purpose of the utimensat() function is to set the access and modi‐
190 fication time of files in directories other than the current working
191 directory without exposure to race conditions. Any part of the path of
192 a file could be changed in parallel to a call to utimes(), resulting in
193 unspecified behavior. By opening a file descriptor for the target
194 directory and using the utimensat() function it can be guaranteed that
195 the changed file is located relative to the desired directory.
196 The standard developers considered including a special case for the
198 permissions required by utimensat() when one tv_nsec field is UTIME_NOW
199 and the other is UTIME_OMIT. One possibility would be to include this
200 case in with the cases where times is a null pointer or both fields are
201 UTIME_NOW, where the call is allowed if the process has write permis‐
202 sion for the file. However, associating write permission with an update
203 to just the last data access timestamp (which is normally updated by
204 read()) did not seem appropriate. The other possibility would be to
205 specify that this one case is allowed if the process has read permis‐
206 sion, but this was felt to be too great a departure from the utime()
207 and utimes() functions on which utimensat() is based. If an application
208 needs to set the last data access timestamp to the current time for a
209 file on which it has read permission but is not the owner, it can do so
210 by opening the file, reading one or more bytes (or reading a directory
211 entry, if the file is a directory), and then closing it.
212
214 None.
215
217 read(), utime()
218 The Base Definitions volume of POSIX.1‐2017, <fcntl.h>, <sys_stat.h>,
220 <sys_time.h>
221
223 Portions of this text are reprinted and reproduced in electronic form
224 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
225 table Operating System Interface (POSIX), The Open Group Base Specifi‐
226 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
227 Electrical and Electronics Engineers, Inc and The Open Group. In the
228 event of any discrepancy between this version and the original IEEE and
229 The Open Group Standard, the original IEEE and The Open Group Standard
230 is the referee document. The original Standard can be obtained online
231 at http://www.opengroup.org/unix/online.html .
232 Any typographical or formatting errors that appear in this page are
234 most likely to have been introduced during the conversion of the source
235 files to man page format. To report such errors, see https://www.ker‐
236 nel.org/doc/man-pages/reporting_bugs.html .
237IEEE/The Open Group 2017 FUTIMENS(3P)