Langue: en

Version: 2009-09-30 (ubuntu - 24/10/10)

Section: 2 (Appels système)


stat, fstat, lstat - get file status


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

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

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

lstat(): _BSD_SOURCE || _XOPEN_SOURCE >= 500


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

stat() stats the file pointed to by path and fills in buf.

lstat() is identical to stat(), except that if path is a symbolic link, then the link itself is stat-ed, not the file that it refers to.

fstat() is identical to stat(), except that the file to be stat-ed 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 file system I/O */
     blkcnt_t  st_blocks;  /* number of 512B blocks allocated */
     time_t    st_atime;   /* time of last access */
     time_t    st_mtime;   /* time of last modification */
     time_t    st_ctime;   /* time of last status change */

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) represents.

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 symlink is the length of the pathname it contains, without a trailing 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 file system I/O. (Writing to a file in smaller chunks may cause an inefficient read-modify-rewrite.)

Not all of the Linux file systems implement all of the time fields. Some file system 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 information (i.e., owner, group, link count, mode, etc.).

The following POSIX macros are defined to check the file type using the st_mode field:

is it a regular file?
character device?
block device?
FIFO (named pipe)?
symbolic link? (Not in POSIX.1-1996.)
socket? (Not in POSIX.1-1996.)

The following flags are defined for 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
S_ISUID 0004000 set UID 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 directory 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.


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


Search permission is denied for one of the directories in the path prefix of path. (See also path_resolution(7).)
fd is bad.
Bad address.
Too many symbolic links encountered while traversing the path.
File name too long.
A component of path does not exist, or path is an empty string.
Out of memory (i.e., kernel memory).
A component of the path prefix of path is not a directory.
(stat()) path refers to a file whose size cannot be represented in the type off_t. This can occur when an application compiled on a 32-bit platform without -D_FILE_OFFSET_BITS=64 calls stat() on a file whose size exceeds (2<<31)-1 bits.


These system calls conform to SVr4, 4.3BSD, POSIX.1-2001.

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.)

POSIX does not describe the S_IFMT, S_IFSOCK, S_IFLNK, S_IFREG, S_IFBLK, S_IFDIR, S_IFCHR, S_IFIFO, S_ISVTX bits, but instead demands the use of the macros S_ISDIR(), etc. 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 userspace)
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.


Since kernel 2.5.48, the stat structure supports nanosecond resolution for the three file timestamp fields. Glibc exposes the nanosecond component of each field using names either of the form st_atim.tv_nsec, if the _BSD_SOURCE or _SVID_SOURCE feature test macro is defined, or of the form st_atimensec, if neither of these macros is defined. On file systems that do not support subsecond timestamps, these nanosecond fields are returned with the value 0.

On Linux, lstat() will generally not trigger automounter action, whereas stat() will.

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.

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 system call provided by the kernel, and repacking the returned information if required for old binaries. Similar remarks apply for fstat() and lstat().


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>
 main(int argc, char *argv[])
     struct stat sb;
     if (argc != 2) {
         fprintf(stderr, "Usage: %s <pathname>\n", argv[0]);
     if (stat(argv[1], &sb) == -1) {
     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));


access(2), chmod(2), chown(2), fstatat(2), readlink(2), utime(2), capabilities(7), symlink(7)


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