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 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
           || /* Since glibc 2.10: */ _POSIX_C_SOURCE >= 200112L

       fstatat():
           Since glibc 2.10:
               _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:
               _ATFILE_SOURCE

DESCRIPTION
       These  functions return information about a file, in the buffer pointed
       to by stat.  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;        /* protection */
               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 the glibc and kernel source code if you need to
       know the details.

       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.).

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

           S_IFMT     0170000   bit mask for the file type bit fields

           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  permissions  compo-
       nent of the st_mode field:

           S_ISUID   0004000   set-user-ID bit
           S_ISGID   0002000   set-group-ID bit (see below)
           S_ISVTX   0001000   sticky bit (see below)

           S_IRWXU     00700   mask for file owner permissions
           S_IRUSR     00400   owner has read permission
           S_IWUSR     00200   owner has write permission
           S_IXUSR     00100   owner has execute permission


           S_IRWXG     00070   mask for group permissions
           S_IRGRP     00040   group has read permission
           S_IWGRP     00020   group has write permission
           S_IXGRP     00010   group has execute permission

           S_IRWXO     00007   mask for permissions for others
                               (not in group)
           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 bad.

       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 component 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 permission 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.

   Underlying kernel interface
       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() (new  in  kernel  2.4;
       slot  __NR_stat64).   The  glibc  stat()  wrapper  function hides these
       details from applications, invoking the most recent version of the sys-
       tem call provided by the kernel, and repacking the returned information
       if required for old binaries.  Similar remarks apply  for  fstat()  and
       lstat().

       The  underlying  system  call  employed  by the glibc fstatat() wrapper
       function is actually called fstatat64().

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 3.74 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
       http://www.kernel.org/doc/man-pages/.

Linux                             2014-08-19                           STAT(2)

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