#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():
fstatat():
These functions return information about a file, in the buffer pointed to by buf. 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 information 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; /* 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; /* 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 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 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 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 information (i.e., owner, group, link count, mode, etc.).
POSIX refers to the st_mode bits corresponding to the mask S_IFMT (see below) as the file type, the 12 bits corresponding to the mask 07777 as the file mode bits and the least significant 9 bits (0777) as the file permission bits.
The following mask values are defined for the file type of the st_mode field:
| S_IFMT | 0170000 | bit mask for the file type bit field |
| 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:
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 mode component of the st_mode field:
| S_ISUID | 04000 | set-user-ID bit |
| S_ISGID | 02000 | set-group-ID bit (see below) |
| S_ISVTX | 01000 | sticky bit (see below) |
| S_IRWXU | 00700 | owner has read, write, and execute permission |
| S_IRUSR | 00400 | owner has read permission |
| S_IWUSR | 00200 | owner has write permission |
| S_IXUSR | 00100 | owner has execute permission |
| S_IRWXG | 00070 | group has read, write, and execute permission |
| S_IRGRP | 00040 | group has read permission |
| S_IWGRP | 00020 | group has write permission |
| S_IXGRP | 00010 | group has execute permission |
| S_IRWXO | 00007 |
others (not in group) have read, write, and execute permission
|
| 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.
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:
See openat(2) for an explanation of the need for fstatat().
The following additional errors can occur for fstatat():
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.) 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* constants 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.
| 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.
For pseudofiles that are autogenerated by the kernel, stat() does not return an accurate value in the st_size field. For example, the value 0 is returned for many files under the /proc directory, while various files under /sys report a size of 4096 bytes, even though the file content is smaller. For such files, one should simply try to read as many bytes as possible (and append '\0' to the returned buffer if it is to be interpreted as a string).
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 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.
The kernel-internal versions of the stat structure dealt with by the different versions are, respectively:
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.
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().
#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); }