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man:lstat

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  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 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() 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 directory 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 defini-
            tion.  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  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

 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 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), utime(2),
     capabilities(7), inode(7), symlink(7)

COLOPHON

     This page is part of release 4.16 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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