fstatat(3p) — Linux manual page

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

PROLOG         top

       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.

NAME         top

       fstatat, lstat, stat — get file status

SYNOPSIS         top

       #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         top

       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         top

       Upon successful completion, these functions shall return 0.
       Otherwise, these functions shall return -1 and set errno to
       indicate the error.

ERRORS         top

       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         top

   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         top

       None.

RATIONALE         top

       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         top

       None.

SEE ALSO         top

       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)

COPYRIGHT         top

       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)