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NAME
fstatat, lstat, stat — get file status
SYNOPSIS
#include <fcntl.h>
#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 continue 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.1‐2017, Section 4.9, 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.1‐2017, 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 information about the link, while stat() shall
return information about the file the link references.
For symbolic links, the st_mode member shall contain meaningful information 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 access mode
of the open file description associated with the file descriptor is not O_SEARCH, the
function shall check whether directory searches are permitted using the current
permissions of the directory underlying the file descriptor. If the access mode is
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 The access mode of the open file description associated with fd is not 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 resolution 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 symbolic 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 purpose of the fstatat() function is to obtain the status of files in directories
other than the current working directory without exposure 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.1‐2017, Section 4.9, 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
1003.1-2017, Standard for Information Technology -- Portable Operating System Interface
(POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/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.kernel.org/doc/man-pages/reporting_bugs.html .