fstat(2)



STAT(2)                    Linux Programmer's Manual                   STAT(2)

NAME
       stat, fstat, lstat, fstatat - get file status

SYNOPSIS
       #include <sys/types.h>
       #include <sys/stat.h>
       #include <unistd.h>

       int stat(const char *pathname, struct stat *statbuf);
       int fstat(int fd, struct stat *statbuf);
       int lstat(const char *pathname, struct stat *statbuf);

       #include <fcntl.h>           /* Definition of AT_* constants */
       #include <sys/stat.h>

       int fstatat(int dirfd, const char *pathname, struct stat *statbuf,
                   int flags);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       lstat():
           /* glibc 2.19 and earlier */ _BSD_SOURCE
               || /* Since glibc 2.20 */ _DEFAULT_SOURCE
               || _XOPEN_SOURCE >= 500
               || /* Since glibc 2.10: */ _POSIX_C_SOURCE >= 200112L

       fstatat():
           Since glibc 2.10:
               _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:
               _ATFILE_SOURCE

DESCRIPTION
       These  functions return information about a file, in the buffer pointed
       to by statbuf.  No permissions are required on the file itself, but--in
       the case of stat(), fstatat(), and lstat()--execute (search) permission
       is required on all of the directories in  pathname  that  lead  to  the
       file.

       stat()  and fstatat() retrieve information about the file pointed to by
       pathname; the differences for fstatat() are described below.

       lstat() is identical to stat(), except that if pathname is  a  symbolic
       link,  then  it returns information about the link itself, not the file
       that it refers to.

       fstat() is identical to stat(), except that the file about which infor-
       mation is to be retrieved is specified by the file descriptor fd.

   The stat structure
       All  of  these system calls return a stat structure, which contains the
       following fields:

           struct stat {
               dev_t     st_dev;         /* ID of device containing file */
               ino_t     st_ino;         /* Inode number */
               mode_t    st_mode;        /* File type and mode */
               nlink_t   st_nlink;       /* Number of hard links */
               uid_t     st_uid;         /* User ID of owner */
               gid_t     st_gid;         /* Group ID of owner */
               dev_t     st_rdev;        /* Device ID (if special file) */
               off_t     st_size;        /* Total size, in bytes */
               blksize_t st_blksize;     /* Block size for filesystem I/O */
               blkcnt_t  st_blocks;      /* Number of 512B blocks allocated */

               /* Since Linux 2.6, the kernel supports nanosecond
                  precision for the following timestamp fields.
                  For the details before Linux 2.6, see NOTES. */

               struct timespec st_atim;  /* Time of last access */
               struct timespec st_mtim;  /* Time of last modification */
               struct timespec st_ctim;  /* Time of last status change */

           #define st_atime st_atim.tv_sec      /* Backward compatibility */
           #define st_mtime st_mtim.tv_sec
           #define st_ctime st_ctim.tv_sec
           };

       Note: the order of fields in the stat structure varies somewhat  across
       architectures.   In  addition,  the  definition above does not show the
       padding bytes that may be present between some fields on various archi-
       tectures.  Consult the glibc and kernel source code if you need to know
       the details.

       Note: for performance and simplicity reasons, different fields  in  the
       stat  structure  may  contain  state information from different moments
       during the execution of the system call.  For example,  if  st_mode  or
       st_uid  is  changed by another process by calling chmod(2) or chown(2),
       stat() might return the old st_mode together with the  new  st_uid,  or
       the old st_uid together with the new st_mode.

       The fields in the stat structure are as follows:

       st_dev This  field  describes  the  device  on which this file resides.
              (The major(3) and minor(3) macros may be useful to decompose the
              device ID in this field.)

       st_ino This field contains the file's inode number.

       st_mode
              This  field  contains  the file type and mode.  See inode(7) for
              further information.

       st_nlink
              This field contains the number of hard links to the file.

       st_uid This field contains the user ID of the owner of the file.

       st_gid This field contains the ID of the group owner of the file.

       st_rdev
              This field describes the device that this  file  (inode)  repre-
              sents.

       st_size
              This  field  gives the size of the file (if it is a regular file
              or a symbolic link) in bytes.  The size of a  symbolic  link  is
              the  length  of  the pathname it contains, without a terminating
              null byte.

       st_blksize
              This field  gives  the  "preferred"  block  size  for  efficient
              filesystem I/O.

       st_blocks
              This field indicates the number of blocks allocated to the file,
              in 512-byte units.  (This may be smaller than  st_size/512  when
              the file has holes.)

       st_atime
              This is the file's last access timestamp.

       st_mtime
              This is the file's last modification timestamp.

       st_ctime
              This is the file's last status change timestamp.

       For further information on the above fields, see inode(7).

   fstatat()
       The  fstatat()  system call operates in exactly the same way as stat(),
       except for the differences described here.

       If the pathname given in pathname is relative, then it  is  interpreted
       relative  to  the  directory  referred  to by the file descriptor dirfd
       (rather than relative to the current working directory of  the  calling
       process, as is done by stat() for a relative pathname).

       If  pathname  is relative and dirfd is the special value AT_FDCWD, then
       pathname is interpreted relative to the current  working  directory  of
       the calling process (like stat()).

       If pathname is absolute, then dirfd is ignored.

       flags  can  either  be 0, or include one or more of the following flags
       ORed:

       AT_EMPTY_PATH (since Linux 2.6.39)
              If pathname is an empty string, operate on the file referred  to
              by  dirfd (which may have been obtained using the open(2) O_PATH
              flag).  In this case, dirfd can refer to any type of  file,  not
              just  a  directory.   If dirfd is AT_FDCWD, the call operates on
              the current working directory.   This  flag  is  Linux-specific;
              define _GNU_SOURCE to obtain its definition.

       AT_NO_AUTOMOUNT (since Linux 2.6.38)
              Don't  automount the terminal ("basename") component of pathname
              if it is a directory that is an automount  point.   This  allows
              the  caller  to  gather attributes of an automount point (rather
              than the location it would mount).  This flag  can  be  used  in
              tools  that  scan  directories to prevent mass-automounting of a
              directory of automount points.  The AT_NO_AUTOMOUNT flag has  no
              effect  if  the mount point has already been mounted over.  This
              flag is Linux-specific; define _GNU_SOURCE to obtain its defini-
              tion.

       AT_SYMLINK_NOFOLLOW
              If  pathname  is a symbolic link, do not dereference it: instead
              return information about the link  itself,  like  lstat().   (By
              default, fstatat() dereferences symbolic links, like stat().)

       See openat(2) for an explanation of the need for fstatat().

RETURN VALUE
       On  success,  zero is returned.  On error, -1 is returned, and errno is
       set appropriately.

ERRORS
       EACCES Search permission is denied for one of the  directories  in  the
              path prefix of pathname.  (See also path_resolution(7).)

       EBADF  fd is not a valid open file descriptor.

       EFAULT Bad address.

       ELOOP  Too many symbolic links encountered while traversing the path.

       ENAMETOOLONG
              pathname is too long.

       ENOENT A  component of pathname does not exist, or pathname is an empty
              string and AT_EMPTY_PATH was not specified in flags.

       ENOMEM Out of memory (i.e., kernel memory).

       ENOTDIR
              A component of the path prefix of pathname is not a directory.

       EOVERFLOW
              pathname or fd refers to a file whose  size,  inode  number,  or
              number  of  blocks  cannot  be represented in, respectively, the
              types off_t, ino_t, or blkcnt_t.  This error can occur when, for
              example,  an  application  compiled on a 32-bit platform without
              -D_FILE_OFFSET_BITS=64 calls stat() on a file whose size exceeds
              (1<<31)-1 bytes.

       The following additional errors can occur for fstatat():

       EBADF  dirfd is not a valid file descriptor.

       EINVAL Invalid flag specified in flags.

       ENOTDIR
              pathname is relative and dirfd is a file descriptor referring to
              a file other than a directory.

VERSIONS
       fstatat() was added to Linux in  kernel  2.6.16;  library  support  was
       added to glibc in version 2.4.

CONFORMING TO
       stat(), fstat(), lstat(): SVr4, 4.3BSD, POSIX.1-2001, POSIX.1.2008.

       fstatat(): POSIX.1-2008.

       According to POSIX.1-2001, lstat() on a symbolic link need return valid
       information only in the st_size field and the file type of the  st_mode
       field  of the stat structure.  POSIX.1-2008 tightens the specification,
       requiring lstat() to return valid information in all fields except  the
       mode bits in st_mode.

       Use of the st_blocks and st_blksize fields may be less portable.  (They
       were introduced in BSD.  The interpretation  differs  between  systems,
       and possibly on a single system when NFS mounts are involved.)

NOTES
       On  Linux,  lstat()  will  generally  not  trigger  automounter action,
       whereas  stat()  will  (but  see  the  description  of  the   fstatat()
       AT_NO_AUTOMOUNT fag, above).

   Timestamp fields
       Older  kernels and older standards did not support nanosecond timestamp
       fields.   Instead,  there  were   three   timestamp   fields--st_atime,
       st_mtime,  and  st_ctime--typed as time_t that recorded timestamps with
       one-second precision.

       Since kernel 2.5.48, the stat structure supports nanosecond  resolution
       for the three file timestamp fields.  The nanosecond components of each
       timestamp are available via names of the form st_atim.tv_nsec, if suit-
       able feature test macros are defined.  Nanosecond timestamps were stan-
       dardized in  POSIX.1-2008,  and,  starting  with  version  2.12,  glibc
       exposes  the  nanosecond  component names if _POSIX_C_SOURCE is defined
       with the value 200809L or greater, or _XOPEN_SOURCE is defined with the
       value  700 or greater.  Up to and including glibc 2.19, the definitions
       of the nanoseconds  components  are  also  defined  if  _BSD_SOURCE  or
       _SVID_SOURCE  is  defined.   If  none  of the aforementioned macros are
       defined, then the nanosecond values are exposed with names of the  form
       st_atimensec.

   C library/kernel differences
       Over  time,  increases  in  the  size of the stat structure have led to
       three successive versions of stat():  sys_stat()  (slot  __NR_oldstat),
       sys_newstat()  (slot __NR_stat), and sys_stat64() (slot __NR_stat64) on
       32-bit platforms such as i386.  The first  two  versions  were  already
       present  in Linux 1.0 (albeit with different names); the last was added
       in Linux 2.4.  Similar remarks apply for fstat() and lstat().

       The kernel-internal versions of the stat structure dealt  with  by  the
       different versions are, respectively:

       __old_kernel_stat
              The  original  structure, with rather narrow fields, and no pad-
              ding.

       stat   Larger st_ino field and padding added to various  parts  of  the
              structure to allow for future expansion.

       stat64 Even  larger  st_ino  field,  larger st_uid and st_gid fields to
              accommodate the Linux-2.4 expansion of UIDs and GIDs to 32 bits,
              and  various  other  enlarged  fields and further padding in the
              structure.  (Various padding bytes were eventually  consumed  in
              Linux  2.6,  with the advent of 32-bit device IDs and nanosecond
              components for the timestamp fields.)

       The glibc stat() wrapper function hides  these  details  from  applica-
       tions,  invoking the most recent version of the system call provided by
       the kernel, and repacking the returned information if required for  old
       binaries.

       On  modern  64-bit  systems,  life is simpler: there is a single stat()
       system call and the kernel deals with a stat  structure  that  contains
       fields of a sufficient size.

       The  underlying  system  call  employed  by the glibc fstatat() wrapper
       function is actually called  fstatat64()  or,  on  some  architectures,
       newfstatat().

EXAMPLE
       The  following program calls stat() and displays selected fields in the
       returned stat structure.

       #include <sys/types.h>
       #include <sys/stat.h>
       #include <time.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <sys/sysmacros.h>

       int
       main(int argc, char *argv[])
       {
           struct stat sb;

           if (argc != 2) {
               fprintf(stderr, "Usage: %s <pathname>\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           if (stat(argv[1], &sb) == -1) {
               perror("stat");
               exit(EXIT_FAILURE);
           }

           printf("ID of containing device:  [%lx,%lx]\n",
                (long) major(sb.st_dev), (long) minor(sb.st_dev));

           printf("File type:                ");

           switch (sb.st_mode & S_IFMT) {
           case S_IFBLK:  printf("block device\n");            break;
           case S_IFCHR:  printf("character device\n");        break;
           case S_IFDIR:  printf("directory\n");               break;
           case S_IFIFO:  printf("FIFO/pipe\n");               break;
           case S_IFLNK:  printf("symlink\n");                 break;
           case S_IFREG:  printf("regular file\n");            break;
           case S_IFSOCK: printf("socket\n");                  break;
           default:       printf("unknown?\n");                break;
           }

           printf("I-node number:            %ld\n", (long) sb.st_ino);

           printf("Mode:                     %lo (octal)\n",
                   (unsigned long) sb.st_mode);

           printf("Link count:               %ld\n", (long) sb.st_nlink);
           printf("Ownership:                UID=%ld   GID=%ld\n",
                   (long) sb.st_uid, (long) sb.st_gid);

           printf("Preferred I/O block size: %ld bytes\n",
                   (long) sb.st_blksize);
           printf("File size:                %lld bytes\n",
                   (long long) sb.st_size);
           printf("Blocks allocated:         %lld\n",
                   (long long) sb.st_blocks);

           printf("Last status change:       %s", ctime(&sb.st_ctime));
           printf("Last file access:         %s", ctime(&sb.st_atime));
           printf("Last file modification:   %s", ctime(&sb.st_mtime));

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       ls(1), stat(1), access(2), chmod(2), chown(2),  readlink(2),  utime(2),
       capabilities(7), inode(7), symlink(7)

COLOPHON
       This  page  is  part of release 4.13 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       https://www.kernel.org/doc/man-pages/.

Linux                             2017-09-15                           STAT(2)

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