1FSTATAT(3P) POSIX Programmer's Manual FSTATAT(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 fstatat, lstat, stat — get file status
13
15 #include <fcntl.h>
16 #include <sys/stat.h>
17 int fstatat(int fd, const char *restrict path,
19 struct stat *restrict buf, int flag);
20 int lstat(const char *restrict path, struct stat *restrict buf);
21 int stat(const char *restrict path, struct stat *restrict buf);
22
24 The stat() function shall obtain information about the named file and
25 write it to the area pointed to by the buf argument. The path argument
26 points to a pathname naming a file. Read, write, or execute permission
27 of the named file is not required. An implementation that provides
28 additional or alternate file access control mechanisms may, under
29 implementation-defined conditions, cause stat() to fail. In particular,
30 the system may deny the existence of the file specified by path.
31 If the named file is a symbolic link, the stat() function shall con‐
33 tinue pathname resolution using the contents of the symbolic link, and
34 shall return information pertaining to the resulting file if the file
35 exists.
36 The buf argument is a pointer to a stat structure, as defined in the
38 <sys/stat.h> header, into which information is placed concerning the
39 file.
40 The stat() function shall update any time-related fields (as described
42 in the Base Definitions volume of POSIX.1‐2017, Section 4.9, File Times
43 Update), before writing into the stat structure.
44 If the named file is a shared memory object, the implementation shall
46 update in the stat structure pointed to by the buf argument the st_uid,
47 st_gid, st_size, and st_mode fields, and only the S_IRUSR, S_IWUSR,
48 S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH file permission bits need be
49 valid. The implementation may update other fields and flags.
50 If the named file is a typed memory object, the implementation shall
52 update in the stat structure pointed to by the buf argument the st_uid,
53 st_gid, st_size, and st_mode fields, and only the S_IRUSR, S_IWUSR,
54 S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH file permission bits need be
55 valid. The implementation may update other fields and flags.
56 For all other file types defined in this volume of POSIX.1‐2017, the
58 structure members st_mode, st_ino, st_dev, st_uid, st_gid, st_atim,
59 st_ctim, and st_mtim shall have meaningful values and the value of the
60 member st_nlink shall be set to the number of links to the file.
61 The lstat() function shall be equivalent to stat(), except when path
63 refers to a symbolic link. In that case lstat() shall return informa‐
64 tion about the link, while stat() shall return information about the
65 file the link references.
66 For symbolic links, the st_mode member shall contain meaningful infor‐
68 mation when used with the file type macros. The file mode bits in
69 st_mode are unspecified. The structure members st_ino, st_dev, st_uid,
70 st_gid, st_atim, st_ctim, and st_mtim shall have meaningful values and
71 the value of the st_nlink member shall be set to the number of (hard)
72 links to the symbolic link. The value of the st_size member shall be
73 set to the length of the pathname contained in the symbolic link not
74 including any terminating null byte.
75 The fstatat() function shall be equivalent to the stat() or lstat()
77 function, depending on the value of flag (see below), except in the
78 case where path specifies a relative path. In this case the status
79 shall be retrieved from a file relative to the directory associated
80 with the file descriptor fd instead of the current working directory.
81 If the access mode of the open file description associated with the
82 file descriptor is not O_SEARCH, the function shall check whether
83 directory searches are permitted using the current permissions of the
84 directory underlying the file descriptor. If the access mode is
85 O_SEARCH, the function shall not perform the check.
86 Values for flag are constructed by a bitwise-inclusive OR of flags from
88 the following list, defined in <fcntl.h>:
89 AT_SYMLINK_NOFOLLOW
91 If path names a symbolic link, the status of the symbolic link is
92 returned.
93 If fstatat() is passed the special value AT_FDCWD in the fd parameter,
95 the current working directory shall be used and the behavior shall be
96 identical to a call to stat() or lstat() respectively, depending on
97 whether or not the AT_SYMLINK_NOFOLLOW bit is set in flag.
98
100 Upon successful completion, these functions shall return 0. Otherwise,
101 these functions shall return -1 and set errno to indicate the error.
102
104 These functions shall fail if:
105 EACCES Search permission is denied for a component of the path prefix.
107 EIO An error occurred while reading from the file system.
109 ELOOP A loop exists in symbolic links encountered during resolution of
111 the path argument.
112 ENAMETOOLONG
114 The length of a component of a pathname is longer than
115 {NAME_MAX}.
116 ENOENT A component of path does not name an existing file or path is an
118 empty string.
119 ENOTDIR
121 A component of the path prefix names an existing file that is
122 neither a directory nor a symbolic link to a directory, or the
123 path argument contains at least one non-<slash> character and
124 ends with one or more trailing <slash> characters and the last
125 pathname component names an existing file that is neither a
126 directory nor a symbolic link to a directory.
127 EOVERFLOW
129 The file size in bytes or the number of blocks allocated to the
130 file or the file serial number cannot be represented correctly
131 in the structure pointed to by buf.
132 The fstatat() function shall fail if:
134 EACCES The access mode of the open file description associated with fd
136 is not O_SEARCH and the permissions of the directory underlying
137 fd do not permit directory searches.
138 EBADF The path argument does not specify an absolute path and the fd
140 argument is neither AT_FDCWD nor a valid file descriptor open
141 for reading or searching.
142 ENOTDIR
144 The path argument is not an absolute path and fd is a file
145 descriptor associated with a non-directory file.
146 These functions may fail if:
148 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
150 resolution of the path argument.
151 ENAMETOOLONG
153 The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
154 tion of a symbolic link produced an intermediate result with a
155 length that exceeds {PATH_MAX}.
156 EOVERFLOW
158 A value to be stored would overflow one of the members of the
159 stat structure.
160 The fstatat() function may fail if:
162 EINVAL The value of the flag argument is not valid.
164 The following sections are informative.
166
168 Obtaining File Status Information
169 The following example shows how to obtain file status information for a
170 file named /home/cnd/mod1. The structure variable buffer is defined
171 for the stat structure.
172 #include <sys/types.h>
175 #include <sys/stat.h>
176 #include <fcntl.h>
177 struct stat buffer;
179 int status;
180 ...
181 status = stat("/home/cnd/mod1", &buffer);
182 Getting Directory Information
184 The following example fragment gets status information for each entry
185 in a directory. The call to the stat() function stores file information
186 in the stat structure pointed to by statbuf. The lines that follow the
187 stat() call format the fields in the stat structure for presentation to
188 the user of the program.
189 #include <sys/types.h>
192 #include <sys/stat.h>
193 #include <dirent.h>
194 #include <pwd.h>
195 #include <grp.h>
196 #include <time.h>
197 #include <locale.h>
198 #include <langinfo.h>
199 #include <stdio.h>
200 #include <stdint.h>
201 struct dirent *dp;
203 struct stat statbuf;
204 struct passwd *pwd;
205 struct group *grp;
206 struct tm *tm;
207 char datestring[256];
208 ...
209 /* Loop through directory entries. */
210 while ((dp = readdir(dir)) != NULL) {
211 /* Get entry's information. */
213 if (stat(dp->d_name, &statbuf) == -1)
214 continue;
215 /* Print out type, permissions, and number of links. */
217 printf("%10.10s", sperm (statbuf.st_mode));
218 printf("%4d", statbuf.st_nlink);
219 /* Print out owner's name if it is found using getpwuid(). */
221 if ((pwd = getpwuid(statbuf.st_uid)) != NULL)
222 printf(" %-8.8s", pwd->pw_name);
223 else
224 printf(" %-8d", statbuf.st_uid);
225 /* Print out group name if it is found using getgrgid(). */
227 if ((grp = getgrgid(statbuf.st_gid)) != NULL)
228 printf(" %-8.8s", grp->gr_name);
229 else
230 printf(" %-8d", statbuf.st_gid);
231 /* Print size of file. */
233 printf(" %9jd", (intmax_t)statbuf.st_size);
234 tm = localtime(&statbuf.st_mtime);
236 /* Get localized date string. */
238 strftime(datestring, sizeof(datestring), nl_langinfo(D_T_FMT), tm);
239 printf(" %s %s\n", datestring, dp->d_name);
241 }
242 Obtaining Symbolic Link Status Information
244 The following example shows how to obtain status information for a sym‐
245 bolic link named /modules/pass1. The structure variable buffer is
246 defined for the stat structure. If the path argument specified the
247 pathname for the file pointed to by the symbolic link (/home/cnd/mod1),
248 the results of calling the function would be the same as those returned
249 by a call to the stat() function.
250 #include <sys/stat.h>
253 struct stat buffer;
255 int status;
256 ...
257 status = lstat("/modules/pass1", &buffer);
258
260 None.
261
263 The intent of the paragraph describing ``additional or alternate file
264 access control mechanisms'' is to allow a secure implementation where a
265 process with a label that does not dominate the file's label cannot
266 perform a stat() function. This is not related to read permission; a
267 process with a label that dominates the file's label does not need read
268 permission. An implementation that supports write-up operations could
269 fail fstat() function calls even though it has a valid file descriptor
270 open for writing.
271 The purpose of the fstatat() function is to obtain the status of files
273 in directories other than the current working directory without expo‐
274 sure to race conditions. Any part of the path of a file could be
275 changed in parallel to a call to stat(), resulting in unspecified
276 behavior. By opening a file descriptor for the target directory and
277 using the fstatat() function it can be guaranteed that the file for
278 which status is returned is located relative to the desired directory.
279
281 None.
282
284 access(), chmod(), fdopendir(), fstat(), mknod(), readlink(), symlink()
285 The Base Definitions volume of POSIX.1‐2017, Section 4.9, File Times
287 Update, <fcntl.h>, <sys_stat.h>, <sys_types.h>
288
290 Portions of this text are reprinted and reproduced in electronic form
291 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
292 table Operating System Interface (POSIX), The Open Group Base Specifi‐
293 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
294 Electrical and Electronics Engineers, Inc and The Open Group. In the
295 event of any discrepancy between this version and the original IEEE and
296 The Open Group Standard, the original IEEE and The Open Group Standard
297 is the referee document. The original Standard can be obtained online
298 at http://www.opengroup.org/unix/online.html .
299 Any typographical or formatting errors that appear in this page are
301 most likely to have been introduced during the conversion of the source
302 files to man page format. To report such errors, see https://www.ker‐
303 nel.org/doc/man-pages/reporting_bugs.html .
304IEEE/The Open Group 2017 FSTATAT(3P)