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Name

stat, fstat, lstat - get file status

Synopsis

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

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

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 filedes.

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 filesystem I/O */ blkcnt_t st_blocks; /* number of 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 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, for example, 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 filesystems implement all of the time fields. Some file system types allow mounting in such a way that file accesses do not cause an update of the st_atime field. (See ‘noatime’ in mount(8) .)

The field st_atime is changed by file accesses, e.g. 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, e.g. 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:

l l l. S_IFMT 0170000 bitmask for the file type bitfields 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.

Linux 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 sub-second timestamps, these nanosecond fields are returned with the value 0.

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.

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(2) .)

EBADF filedes is bad.

EFAULT Bad address.

ELOOP Too many symbolic links encountered while traversing the path.

ENAMETOOLONG
File name too long.

ENOENT A component of the path path does not exist, or the path is an empty string.

ENOMEM Out of memory (i.e. kernel memory).

ENOTDIR
A component of the path is not a directory.

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:

l l l l l. 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 non-directories: don’t cache this file (SunOS) On directories: restricted deletion flag (SVIDv4.2)
0400 S_ISGID
002000 set-group-ID on execution (V7) for directories: use BSD semantics for propagation of GID 0400 S_ENFMT 002000 SysV 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.

See Also

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

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