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fstat
Langue: en
Version: 2009-09-30 (ubuntu - 24/10/10)
Section: 2 (Appels système)
Sommaire
NAME
stat, fstat, lstat - get file statusSYNOPSIS
#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
DESCRIPTION
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:
-
- 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 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.
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 path. (See also path_resolution(7).)
- EBADF
- fd is bad.
- EFAULT
- Bad address.
- ELOOP
- Too many symbolic links encountered while traversing the path.
- ENAMETOOLONG
- File name too long.
- ENOENT
- A component of path does not exist, or path is an empty string.
- ENOMEM
- Out of memory (i.e., kernel memory).
- ENOTDIR
- A component of the path prefix of path is not a directory.
- EOVERFLOW
- (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.
CONFORMING TO
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.
NOTES
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().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
access(2), chmod(2), chown(2), fstatat(2), readlink(2), utime(2), capabilities(7), symlink(7)COLOPHON
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