|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
|
|
|
FSTATAT(3P) POSIX Programmer's Manual FSTATAT(3P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
fstatat, lstat, stat — get file status
#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);
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.
Upon successful completion, these functions shall return 0.
Otherwise, these functions shall return -1 and set errno to
indicate the error.
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.
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);
None.
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.
None.
access(3p), chmod(3p), fdopendir(3p), fstat(3p), mknod(3p),
readlink(3p), symlink(3p)
The Base Definitions volume of POSIX.1‐2017, Section 4.9, File
Times Update, fcntl.h(0p), sys_stat.h(0p), sys_types.h(0p)
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 .
IEEE/The Open Group 2017 FSTATAT(3P)
Pages that refer to this page: sys_stat.h(0p), du(1p), find(1p), ls(1p), pax(1p), access(3p), chmod(3p), fchmod(3p), fdopendir(3p), fstat(3p), ftw(3p), glob(3p), lstat(3p), mknod(3p), nftw(3p), posix_spawn(3p), readdir(3p), readlink(3p), stat(3p), symlink(3p), utime(3p)
|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|