FSTATAT(3P) POSIX Programmer's Manual FSTATAT(3P)
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NAME
fstatat, lstat, stat -- get file status
SYNOPSIS
#include <sys/stat.h>
int fstatat(int fd, const char *restrict path,
struct stat *restrict buf, int flag);
int lstat(const char *restrict path, struct stat *restrict buf);
int stat(const char *restrict path, struct stat *restrict buf);
DESCRIPTION
The stat() function shall obtain information about the named file and
write it to the area pointed to by the buf argument. The path argument
points to a pathname naming a file. Read, write, or execute permission
of the named file is not required. An implementation that provides
additional or alternate file access control mechanisms may, under
implementation-defined conditions, cause stat() to fail. In particular,
the system may deny the existence of the file specified by path.
If the named file is a symbolic link, the stat() function shall con-
tinue pathname resolution using the contents of the symbolic link, and
shall return information pertaining to the resulting file if the file
exists.
The buf argument is a pointer to a stat structure, as defined in the
<sys/stat.h> header, into which information is placed concerning the
file.
The stat() function shall update any time-related fields (as described
in the Base Definitions volume of POSIX.1-2008, Section 4.8, File Times
Update), before writing into the stat structure.
If the named file is a shared memory object, the implementation shall
update in the stat structure pointed to by the buf argument the st_uid,
st_gid, st_size, and st_mode fields, and only the S_IRUSR, S_IWUSR,
S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH file permission bits need be
valid. The implementation may update other fields and flags.
If the named file is a typed memory object, the implementation shall
update in the stat structure pointed to by the buf argument the st_uid,
st_gid, st_size, and st_mode fields, and only the S_IRUSR, S_IWUSR,
S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH file permission bits need be
valid. The implementation may update other fields and flags.
For all other file types defined in this volume of POSIX.1-2008, the
structure members st_mode, st_ino, st_dev, st_uid, st_gid, st_atim,
st_ctim, and st_mtim shall have meaningful values and the value of the
member st_nlink shall be set to the number of links to the file.
The lstat() function shall be equivalent to stat(), except when path
refers to a symbolic link. In that case lstat() shall return informa-
tion about the link, while stat() shall return information about the
file the link references.
For symbolic links, the st_mode member shall contain meaningful infor-
mation when used with the file type macros. The file mode bits in
st_mode are unspecified. The structure members st_ino, st_dev, st_uid,
st_gid, st_atim, st_ctim, and st_mtim shall have meaningful values and
the value of the st_nlink member shall be set to the number of (hard)
links to the symbolic link. The value of the st_size member shall be
set to the length of the pathname contained in the symbolic link not
including any terminating null byte.
The fstatat() function shall be equivalent to the stat() or lstat()
function, depending on the value of flag (see below), except in the
case where path specifies a relative path. In this case the status
shall be retrieved from a file relative to the directory associated
with the file descriptor fd instead of the current working directory.
If the file descriptor was opened without O_SEARCH, the function shall
check whether directory searches are permitted using the current per-
missions of the directory underlying the file descriptor. If the file
descriptor was opened with O_SEARCH, the function shall not perform the
check.
Values for flag are constructed by a bitwise-inclusive OR of flags from
the following list, defined in <fcntl.h>:
AT_SYMLINK_NOFOLLOW
If path names a symbolic link, the status of the symbolic link is
returned.
If fstatat() is passed the special value AT_FDCWD in the fd parameter,
the current working directory shall be used and the behavior shall be
identical to a call to stat() or lstat() respectively, depending on
whether or not the AT_SYMLINK_NOFOLLOW bit is set in flag.
RETURN VALUE
Upon successful completion, these functions shall return 0. Otherwise,
these functions shall return -1 and set errno to indicate the error.
ERRORS
These functions shall fail if:
EACCES Search permission is denied for a component of the path prefix.
EIO An error occurred while reading from the file system.
ELOOP A loop exists in symbolic links encountered during resolution of
the path argument.
ENAMETOOLONG
The length of a component of a pathname is longer than
{NAME_MAX}.
ENOENT A component of path does not name an existing file or path is an
empty string.
ENOTDIR
A component of the path prefix names an existing file that is
neither a directory nor a symbolic link to a directory, or the
path argument contains at least one non-<slash> character and
ends with one or more trailing <slash> characters and the last
pathname component names an existing file that is neither a
directory nor a symbolic link to a directory.
EOVERFLOW
The file size in bytes or the number of blocks allocated to the
file or the file serial number cannot be represented correctly
in the structure pointed to by buf.
The fstatat() function shall fail if:
EACCES fd was not opened with O_SEARCH and the permissions of the
directory underlying fd do not permit directory searches.
EBADF The path argument does not specify an absolute path and the fd
argument is neither AT_FDCWD nor a valid file descriptor open
for reading or searching.
ENOTDIR
The path argument is not an absolute path and fd is a file
descriptor associated with a non-directory file.
These functions may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
resolution of the path argument.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname resolu-
tion of a symbolic link produced an intermediate result with a
length that exceeds {PATH_MAX}.
EOVERFLOW
A value to be stored would overflow one of the members of the
stat structure.
The fstatat() function may fail if:
EINVAL The value of the flag argument is not valid.
The following sections are informative.
EXAMPLES
Obtaining File Status Information
The following example shows how to obtain file status information for a
file named /home/cnd/mod1. The structure variable buffer is defined
for the stat structure.
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
struct stat buffer;
int status;
...
status = stat("/home/cnd/mod1", &buffer);
Getting Directory Information
The following example fragment gets status information for each entry
in a directory. The call to the stat() function stores file information
in the stat structure pointed to by statbuf. The lines that follow the
stat() call format the fields in the stat structure for presentation to
the user of the program.
#include <sys/types.h>
#include <sys/stat.h>
#include <dirent.h>
#include <pwd.h>
#include <grp.h>
#include <time.h>
#include <locale.h>
#include <langinfo.h>
#include <stdio.h>
#include <stdint.h>
struct dirent *dp;
struct stat statbuf;
struct passwd *pwd;
struct group *grp;
struct tm *tm;
char datestring[256];
...
/* Loop through directory entries. */
while ((dp = readdir(dir)) != NULL) {
/* Get entry's information. */
if (stat(dp->d_name, &statbuf) == -1)
continue;
/* Print out type, permissions, and number of links. */
printf("%10.10s", sperm (statbuf.st_mode));
printf("%4d", statbuf.st_nlink);
/* Print out owner's name if it is found using getpwuid(). */
if ((pwd = getpwuid(statbuf.st_uid)) != NULL)
printf(" %-8.8s", pwd->pw_name);
else
printf(" %-8d", statbuf.st_uid);
/* Print out group name if it is found using getgrgid(). */
if ((grp = getgrgid(statbuf.st_gid)) != NULL)
printf(" %-8.8s", grp->gr_name);
else
printf(" %-8d", statbuf.st_gid);
/* Print size of file. */
printf(" %9jd", (intmax_t)statbuf.st_size);
tm = localtime(&statbuf.st_mtime);
/* Get localized date string. */
strftime(datestring, sizeof(datestring), nl_langinfo(D_T_FMT), tm);
printf(" %s %s\n", datestring, dp->d_name);
}
Obtaining Symbolic Link Status Information
The following example shows how to obtain status information for a sym-
bolic link named /modules/pass1. The structure variable buffer is
defined for the stat structure. If the path argument specified the
pathname for the file pointed to by the symbolic link (/home/cnd/mod1),
the results of calling the function would be the same as those returned
by a call to the stat() function.
#include <sys/stat.h>
struct stat buffer;
int status;
...
status = lstat("/modules/pass1", &buffer);
APPLICATION USAGE
None.
RATIONALE
The intent of the paragraph describing ``additional or alternate file
access control mechanisms'' is to allow a secure implementation where a
process with a label that does not dominate the file's label cannot
perform a stat() function. This is not related to read permission; a
process with a label that dominates the file's label does not need read
permission. An implementation that supports write-up operations could
fail fstat() function calls even though it has a valid file descriptor
open for writing.
The lstat() function is not required to update the time-related fields
if the named file is not a symbolic link. While the st_uid, st_gid,
st_atim, st_mtim, and st_ctim members of the stat structure may apply
to a symbolic link, they are not required to do so. No functions in
POSIX.1-2008 are required to maintain any of these time fields.
The purpose of the fstatat() function is to obtain the status of files
in directories other than the current working directory without expo-
sure to race conditions. Any part of the path of a file could be
changed in parallel to a call to stat(), resulting in unspecified
behavior. By opening a file descriptor for the target directory and
using the fstatat() function it can be guaranteed that the file for
which status is returned is located relative to the desired directory.
FUTURE DIRECTIONS
None.
SEE ALSO
access(), chmod(), fdopendir(), fstat(), mknod(), readlink(), symlink()
The Base Definitions volume of POSIX.1-2008, Section 4.8, File Times
Update, <fcntl.h>, <sys_stat.h>, <sys_types.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker-
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 FSTATAT(3P)
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