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

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

       int fstatat(int dirfd, const char *pathname, struct stat *buf,
                   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 buf.  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.

       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;     /* blocksize 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 st_dev 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.)

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

       The  st_size  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.

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

       The  st_blksize  field  gives  the  "preferred" blocksize for efficient
       filesystem I/O.  (Writing to a file in  smaller  chunks  may  cause  an
       inefficient read-modify-rewrite.)

       Not  all  of  the  Linux  filesystems implement all of the time fields.
       Some filesystem types allow mounting in such a  way  that  file  and/or
       directory  accesses do not cause an update of the st_atime field.  (See
       noatime, nodiratime, and relatime in mount(8), and related  information
       in mount(2).)  In addition, st_atime is not updated if a file is opened
       with the O_NOATIME; see open(2).

       The field st_atime  is  changed  by  file  accesses,  for  example,  by
       execve(2),  mknod(2), pipe(2), utime(2), and read(2) (of more than zero
       bytes).  Other routines, like mmap(2), may or may not update st_atime.

       The field st_mtime is changed by file modifications,  for  example,  by
       mknod(2),  truncate(2),  utime(2),  and  write(2)  (of  more  than zero
       bytes).  Moreover, st_mtime of a directory is changed by  the  creation
       or  deletion  of  files  in  that directory.  The st_mtime field is not
       changed for changes in owner, group, hard link count, or mode.

       The field st_ctime is changed by writing or by setting  inode  informa-
       tion (i.e., owner, group, link count, mode, etc.).

       POSIX  refers to the st_mode bits corresponding to the mask S_IFMT (see
       below) as the file type, the 12 bits corresponding to the mask 07777 as
       the  file mode bits and the least significant 9 bits (0777) as the file
       permission bits.

       The following mask values are defined for the file type of the  st_mode
       field:

           S_IFMT     0170000   bit mask for the file type bit field

           S_IFSOCK   0140000   socket
           S_IFLNK    0120000   symbolic link
           S_IFREG    0100000   regular file
           S_IFBLK    0060000   block device
           S_IFDIR    0040000   directory
           S_IFCHR    0020000   character device
           S_IFIFO    0010000   FIFO

       Thus, to test for a regular file (for example), one could write:

           stat(pathname, &sb);
           if ((sb.st_mode & S_IFMT) == S_IFREG) {
               /* Handle regular file */
           }

       Because  tests  of  the  above  form  are common, additional macros are
       defined by POSIX to allow the test of the file type in  st_mode  to  be
       written more concisely:

           S_ISREG(m)  is it a regular file?

           S_ISDIR(m)  directory?

           S_ISCHR(m)  character device?

           S_ISBLK(m)  block device?

           S_ISFIFO(m) FIFO (named pipe)?

           S_ISLNK(m)  symbolic link?  (Not in POSIX.1-1996.)

           S_ISSOCK(m) socket?  (Not in POSIX.1-1996.)

       The preceding code snippet could thus be rewritten as:

           stat(pathname, &sb);
           if (S_ISREG(sb.st_mode)) {
               /* Handle regular file */
           }

       The definitions of most of the above file type test macros are provided
       if any of the following feature test macros is defined: _BSD_SOURCE (in
       glibc  2.19  and earlier), _SVID_SOURCE (in glibc 2.19 and earlier), or
       _DEFAULT_SOURCE (in glibc 2.20 and later).  In addition, definitions of
       all  of the above macros except S_IFSOCK and S_ISSOCK() are provided if
       _XOPEN_SOURCE is defined.  The  definition  of  S_IFSOCK  can  also  be
       exposed by defining _XOPEN_SOURCE with a value of 500 or greater.

       The definition of S_ISSOCK() is exposed if any of the following feature
       test macros is  defined:  _BSD_SOURCE  (in  glibc  2.19  and  earlier),
       _DEFAULT_SOURCE  (in  glibc 2.20 and later), _XOPEN_SOURCE with a value
       of 500 or greater, or  _POSIX_C_SOURCE  with  a  value  of  200112L  or
       greater.

       The  following  mask  values are defined for the file mode component of
       the st_mode field:

           S_ISUID     04000   set-user-ID bit
           S_ISGID     02000   set-group-ID bit (see below)
           S_ISVTX     01000   sticky bit (see below)

           S_IRWXU     00700   owner has read, write, and execute permission
           S_IRUSR     00400   owner has read permission
           S_IWUSR     00200   owner has write permission
           S_IXUSR     00100   owner has execute permission

           S_IRWXG     00070   group has read, write, and execute permission
           S_IRGRP     00040   group has read permission
           S_IWGRP     00020   group has write permission
           S_IXGRP     00010   group has execute permission

           S_IRWXO     00007   others (not in group) have read,  write,  and
                               execute permission
           S_IROTH     00004   others have read permission
           S_IWOTH     00002   others have write permission
           S_IXOTH     00001   others have execute permission

       The  set-group-ID bit (S_ISGID) has several special uses.  For a direc-
       tory, it indicates that BSD semantics is to be used for that directory:
       files created there inherit their group ID from the directory, not from
       the effective group ID of the creating process, and directories created
       there will also get the S_ISGID bit set.  For a file that does not have
       the group execution bit (S_IXGRP) set, the set-group-ID  bit  indicates
       mandatory file/record locking.

       The  sticky  bit  (S_ISVTX)  on  a  directory means that a file in that
       directory can be renamed or deleted only by the owner of the  file,  by
       the owner of the directory, and by a privileged process.

   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).  If dirfd is AT_FDCWD, the call operates on  the  current
              working directory.  In this case, dirfd can refer to any type of
              file, not just a 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.

       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.)  If you
       need to obtain the definition of the blkcnt_t or blksize_t  types  from
       <sys/stat.h>,  then  define _XOPEN_SOURCE with the value 500 or greater
       (before including any header files).

       POSIX.1-1990 did not describe the S_IFMT, S_IFSOCK,  S_IFLNK,  S_IFREG,
       S_IFBLK,  S_IFDIR,  S_IFCHR,  S_IFIFO,  S_ISVTX  constants, but instead
       demanded the use of the macros S_ISDIR(), and so on.   The  S_IF*  con-
       stants are present in POSIX.1-2001 and later.

       The  S_ISLNK()  and S_ISSOCK() macros are not in POSIX.1-1996, but both
       are present in POSIX.1-2001; the former is from SVID 4, the latter from
       SUSv2.

       UNIX V7 (and later systems) had S_IREAD, S_IWRITE, S_IEXEC, where POSIX
       prescribes the synonyms S_IRUSR, S_IWUSR, S_IXUSR.

   Other systems
       Values that have been (or are) in use on various systems:

       hex    name       ls   octal    description
       f000   S_IFMT          170000   mask for file type
       0000                   000000   SCO out-of-service inode; BSD
                                       unknown type; SVID-v2 and XPG2 have
                                       both 0 and 0100000 for ordinary file
       1000   S_IFIFO    p|   010000   FIFO (named pipe)
       2000   S_IFCHR    c    020000   character special (V7)
       3000   S_IFMPC         030000   multiplexed character special (V7)
       4000   S_IFDIR    d/   040000   directory (V7)
       5000   S_IFNAM         050000   XENIX named special file with two
                                       subtypes, distinguished by st_rdev
                                       values 1, 2
       0001   S_INSEM    s    000001   XENIX semaphore subtype of IFNAM
       0002   S_INSHD    m    000002   XENIX shared data subtype of IFNAM
       6000   S_IFBLK    b    060000   block special (V7)
       7000   S_IFMPB         070000   multiplexed block special (V7)
       8000   S_IFREG    -    100000   regular (V7)
       9000   S_IFCMP         110000   VxFS compressed
       9000   S_IFNWK    n    110000   network special (HP-UX)
       a000   S_IFLNK    l@   120000   symbolic link (BSD)
       b000   S_IFSHAD        130000   Solaris shadow inode for ACL (not
                                       seen by user space)
       c000   S_IFSOCK   s=   140000   socket (BSD; also "S_IFSOC" on VxFS)
       d000   S_IFDOOR   D>   150000   Solaris door
       e000   S_IFWHT    w%   160000   BSD whiteout (not used for inode)
       0200   S_ISVTX         001000   sticky bit: save swapped text even
                                       after use (V7)
                                       reserved (SVID-v2)
                                       On nondirectories: don't cache this
                                       file (SunOS)
                                       On directories: restricted deletion
                                       flag (SVID-v4.2)
       0400   S_ISGID         002000   set-group-ID on execution (V7)
                                       for directories: use BSD semantics
                                       for propagation of GID
       0400   S_ENFMT         002000   System V file locking enforcement
                                       (shared with S_ISGID)
       0800   S_ISUID         004000   set-user-ID on execution (V7)
       0800   S_CDF           004000   directory is a context dependent
                                       file (HP-UX)

       A sticky command appeared in Version 32V AT&T UNIX.

NOTES
       On  Linux,  lstat()  will  generally  not  trigger  automounter action,
       whereas stat() will (but see fstatat(2)).

       For most files under the /proc directory, stat() does  not  return  the
       file  size in the st_size field; instead the field is returned with the
       value 0.

   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 the
       _BSD_SOURCE or _SVID_SOURCE feature test macro is defined.   Nanosecond
       timestamps  are nowadays standardized, starting with POSIX.1-2008, and,
       starting with version 2.12, glibc also 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.  If none  of
       the  aforementioned  macros are defined, then the nanosecond values are
       exposed with names of the form st_atimensec.

       Nanosecond timestamps are supported on XFS, JFS, Btrfs, and ext4 (since
       Linux  2.6.23).  Nanosecond timestamps are not supported in ext2, ext3,
       and Reiserfs.  On filesystems that do not support subsecond timestamps,
       the nanosecond fields are returned with the value 0.

   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
                     padding.

              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 time-
                     stamp 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>

       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("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), symlink(7)

COLOPHON
       This page is part of release 4.06 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                             2016-03-15                           STAT(2)

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