STAT(2)

NAME
stat, fstat, lstat - get file status

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

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

DESCRIPTION

These functions return information about the specified file. You do not need any access rights to the file to get this information but you need search rights to all directories named in the path leading to the file.

stat stats the file pointed to by file_name and fills in buf. lstat is identical to stat, except in the case of a symbolic link, where the link itself is stat-ed, not the file that it refers to. fstat is identical to stat, only the open file pointed to by filedes (as returned by open(2)) is stat-ed in place of file_name.

They all return a stat structure, which contains the following fields:

    struct stat {
        dev_t         st_dev;      /* device */
        ino_t         st_ino;      /* inode */
        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 type (if inode device) */
        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 value st_size gives the size of the file (if it is a regular file or a symlink) in bytes. The size of a symlink is the length of the pathname it contains, without trailing NUL. The value st_blocks gives the size of the file in 512-byte blocks. (This may be smaller than st_size/512 e.g. when the file has holes.) The value st_blksize 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:

    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?

    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 | 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 GID 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 permisson
S_IXOTH | 00001 | others have execute permission

The set GID 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 gid 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, it 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 root.

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

ERRORS

EBADF
    filedes is bad.

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

ENOTDIR
    A component of the path is not a directory.

ELOOP
    Too many symbolic links encountered while traversing the path.

EFAULT
    Bad address.

EACCES
    Permission denied.

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

ENAMETOOLONG
    File name too long.

CONFORMING TO
The stat and fstat calls conform to SVr4, SVID, POSIX, X/OPEN, BSD 4.3. The lstat call conforms to 4.3BSD and SVr4. SVr4 documents additional fstat error conditions EINTR, ENOLINK, and EOVERFLOW. SVr4 documents additional stat and lstat error conditions EACCES, EINTR, EMULTIHOP, ENOLINK, and EOVERFLOW. Use of the st_blocks and st_blksize fields may be less portable. (They were introduced in BSD. Are not specified by POSIX. 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 will be in the next POSIX standard; the former is from SVID 4v2, 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 non-directories: 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 | SysV file locking enforcement (shared w/ 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
chmod(2), chown(2), readlink(2), utime(2)