man_2_fstat.txt

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 path‐
       name 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 re‐
       turns information about the link itself, not the file that it refers to.

       fstat() is identical to stat(), except that the file about which information 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 architectures.  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 informa‐
              tion.

       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) represents.

       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 is a more general interface for accessing file information
       which can still provide exactly the behavior of each of stat(), lstat(), and fstat().

       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() and lstat() for a  rela‐
       tive pathname).

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

       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, and the behavior of fstatat()
              is similar to that of fstat().  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  di‐
              rectory that is an automount point.  This allows the caller to gather attributes
              of an automount point (rather than the location it would  mount).   Since  Linux
              4.14,  also  don't instantiate a nonexistent name in an on-demand directory such
              as used for automounter indirect maps.  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
              definition.  Both stat() and lstat() act as though AT_NO_AUTOMOUNT was set.

       AT_SYMLINK_NOFOLLOW
              If pathname is a symbolic link, do not dereference it: instead  return  informa‐
              tion  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  appropri‐
       ately.

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 is a dangling symbolic link.

       ENOENT 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 ex‐
              ceeds (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
   Timestamp fields
       Older  kernels  and  older  standards did not support nanosecond timestamp fields.  In‐
       stead, 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  suitable  feature  test macros are defined.
       Nanosecond timestamps were standardized 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  aforemen‐
       tioned  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  ver‐
       sions  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  even‐
              tually  consumed in Linux 2.6, with the advent of 32-bit device IDs and nanosec‐
              ond components for the timestamp fields.)

       The glibc stat() wrapper function hides these details from applications,  invoking  the
       most  recent  version  of the system call provided by the kernel, and repacking the re‐
       turned 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 lstat() 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 (lstat(argv[1], &sb) == -1) {
               perror("lstat");
               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), statx(2), utime(2), capa‐
       bilities(7), inode(7), symlink(7)

COLOPHON
       This page is part of release 5.05 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                                     2019-03-06                                   STAT(2)