FSTATAT(3)                 POSIX Programmer's Manual                FSTATAT(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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 .



IEEE/The Open Group                  2017                           FSTATAT(3)
