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Manual page for STAT(2)

stat, lstat, fstat - (BSD version) get file status

SYNOPSIS

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

stat(path, buf) char *path; struct stat *buf;

lstat(path, buf) char *path; struct stat *buf;

fstat(fd, buf) int fd; struct stat *buf;

DESCRIPTION

This is the BSD specification for stat. For the POSIX specification, see stat(2P).

Stat obtains information about the file path. Read, write or execute permission of the named file is not required, but all directories listed in the path name leading to the file must be reachable.

Lstat is like stat except in the case where the named file is a symbolic link, in which case lstat returns information about the link, while stat returns information about the file the link references.

Fstat obtains the same information about an open file referenced by the argument descriptor, such as would be obtained by an open call.

Buf is a pointer to a stat structure into which information is placed concerning the file. The contents of the structure pointed to by buf

     struct stat {
	dev_t	st_dev;	/* device inode resides on */
	ino_t	st_ino;	/* this inode's number */
	u_short	st_mode;	/* protection */
	short	st_nlink;	/* number of hard links to the file */
	uid_t	st_uid;	/* user-id of owner */
	gid_t	st_gid;	/* group-id of owner */
	dev_t	st_rdev;	/* the device type, for inode that is device */
	off_t	st_size;	/* total size of file */
	time_t	st_atime;	/* file last access time */
	int	st_spare1;
	time_t	st_mtime;	/* file last modify time */
	int	st_spare2;
	time_t	st_ctime;	/* file last status change time */
	int	st_spare3;
	long	st_blksize;	/* optimal blocksize for file system i/o ops */
	long	st_blocks;	/* actual number of blocks allocated */
	long	st_spare4[2];
    };

st_atime: Time when file data was last read or modified. Changed by the following system calls: mknod.2 utimes.2 read.2 and write.2 For reasons of efficiency, st_atime is not set when a directory is searched, although this would be more logical.
st_mtime: Time when data was last modified. It is not set by changes of owner, group, link count, or mode. Changed by the following system calls: mknod.2 utimes.2 write.2
st_ctime: Time when file status was last changed. It is set both both by writing and changing the i-node. Changed by the following system calls: chmod.2 chown.2 link.2 mknod.2 rename.2 unlink.2 utimes.2 write.2

The status information word st_mode has bits:

#define S_IFMT	0170000	/* type of file */
#define    S_IFDIR	0040000	/* directory */
#define    S_IFCHR	0020000	/* character special */
#define    S_IFBLK	0060000	/* block special */
#define    S_IFREG	0100000	/* regular */
#define    S_IFLNK	0120000	/* symbolic link */
#define    S_IFSOCK	0140000	/* socket */
#define S_ISUID	0004000	/* set user id on execution */
#define S_ISGID	0002000	/* set group id on execution */
#define S_ISVTX	0001000	/* save swapped text even after use */
#define S_IREAD	0000400	/* read permission, owner */
#define S_IWRITE	0000200	/* write permission, owner */
#define S_IEXEC	0000100	/* execute/search permission, owner */

The mode bits 0000070 and 0000007 encode group and others permissions (see chmod.2

RETURN VALUE

Upon successful completion a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS

Stat and lstat will fail if one or more of the following are true:

[ENOTDIR]: A component of the path prefix is not a directory.
[EINVAL]: The pathname contains a character with the high-order bit set.
[ENAMETOOLONG]: A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
[ENOENT]: The named file does not exist.
[EACCES]: Search permission is denied for a component of the path prefix.
[ELOOP]: Too many symbolic links were encountered in translating the pathname.
[EFAULT]: Buf or name points to an invalid address.
[EIO]: An I/O error occurred while reading from or writing to the file system.

Fstat will fail if one or both of the following are true:

[EBADF]: Fildes is not a valid open file descriptor.
[EFAULT]: Buf points to an invalid address.
[EIO]: An I/O error occurred while reading from or writing to the file system.

CAVEAT

The fields in the stat structure currently marked st_spare1, st_spare2, and st_spare3 are present in preparation for inode time stamps expanding to 64 bits. This, however, can break certain programs that depend on the time stamps being contiguous (in calls to utimes.2

BUGS

Applying fstat to a socket (and thus to a pipe) returns a zeroed buffer, except for the blocksize field, and a unique device and inode number.