NAME

stat, lstat, fstat, fstatat — get file status

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/stat.h>

int
stat(const char *path, struct stat *sb);

int
lstat(const char *path, struct stat *sb);

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

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

int
fstatat(int fd, const char *path, struct stat *sb, int flag);

DESCRIPTION

The stat() function obtains information about the file pointed to by 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 searchable.

The function 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. The fstat() function obtains the same information about an open file known by the file descriptor fd.

fstatat() works the same way as stat() (or lstat() if AT_SYMLINK_NOFOLLOW is set in flag) except if path is relative. In that case, it is looked up from a directory whose file descriptor was passed as fd. Search permission is required on this directory. fd can be set to AT_FDCWD in order to specify the current directory.

The sb argument is a pointer to a stat structure as defined by <sys/stat.h> and into which information is placed concerning the file.

The Standard Structure

The following standards-compliant fields are defined in the structure:

Type	Entry	Description
`dev_t`	st_dev	device ID containing the file
`ino_t`	st_ino	serial number of the file (inode number)
`mode_t`	st_mode	mode of the file
`nlink_t`	st_nlink	number of hard links to the file
`uid_t`	st_uid	user ID of the owner
`gid_t`	st_gid	group ID of the owner
`dev_t`	st_rdev	device type (character or block special)
`off_t`	st_size	size of the file in bytes
`time_t`	st_atime	time of last access
`time_t`	st_mtime	time of last data modification
`time_t`	st_ctime	time of last file status change
`blksize_t`	st_blksize	preferred I/O block size (fs-specific)
`blkcnt_t`	st_blocks	blocks allocated for the file

These are specified in the IEEE Std 1003.1-2004 (“POSIX.1”) standard. The st_ino and st_dev fields taken together uniquely identify the file within the system. Most of the types are defined in types(3).

The time-related fields are:

st_atime: Time when file data was last accessed. Changed by the mknod(2), utimes(2), and read(2) system calls.
st_mtime: Time when file data was last modified. Changed by the mknod(2), utimes(2), and write(2) system calls.
st_ctime: Time when file status was last changed (file metadata modification). Changed by the chflags(2), chmod(2), chown(2), link(2), mknod(2), rename(2), unlink(2), utimes(2), and write(2) system calls.

The size-related fields of the struct stat are as follows:

st_size: The size of the file in bytes. The meaning of the size reported for a directory is file system dependent. Some file systems (e.g. FFS) return the total size used for the directory metadata, possibly including free slots; others (notably ZFS) return the number of entries in the directory. Some may also return other things or always report zero.
st_blksize: The optimal I/O block size for the file.
st_blocks: The actual number of blocks allocated for the file in 512-byte units. As short symbolic links are stored in the inode, this number may be zero.

The status information word st_mode contains bits that define the access mode (see chmod(2)) and the type (see dirent(3)) of the file. The following macros can be used to test whether a file is of the specified type. The value m supplied to the macros is the value of st_mode.

S_ISBLK(m): Test for a block special file.
S_ISCHR(m): Test for a character special file.
S_ISDIR(m): Test for a directory.
S_ISFIFO(m): Test for a pipe or FIFO special file.
S_ISLNK(m): Test for a symbolic link.
S_ISREG(m): Test for a regular file.
S_ISSOCK(m): Test for a socket.
S_ISWHT(m): Test for a whiteout file.

The macros evaluate to a non-zero value if the test is true or to the value 0 if the test is false.

NetBSD Extensions

The following additional NetBSD specific fields are present:

Type	Entry	Description
`long`	st_atimensec	last access (nanoseconds)
`long`	st_mtimensec	last modification (nanoseconds)
`long`	st_ctimensec	last status change (nanoseconds)
`time_t`	st_birthtime	time of inode creation
`long`	st_birthtimensec	inode creation (nanoseconds)
`uint32_t`	st_flags	user defined flags for the file
`uint32_t`	st_gen	file generation number
`uint32_t`	st_spare[2]	implementation detail

However, if _NETBSD_SOURCE is furthermore defined, instead of the above, the following are present in the structure:

Type	Entry	Description
`struct timespec`	st_atimespec	time of last access
`struct timespec`	st_mtimespec	time of last modification
`struct timespec`	st_birthtimespec	time of creation
`uint32_t`	st_flags	user defined flags
`uint32_t`	st_gen	file generation number
`uint32_t`	st_spare[2]	implementation detail

In this case the following macros are provided for convenience:

#if defined(_NETBSD_SOURCE)
  #define st_atime                st_atimespec.tv_sec
  #define st_atimensec            st_atimespec.tv_nsec
  #define st_mtime                st_mtimespec.tv_sec
  #define st_mtimensec            st_mtimespec.tv_nsec
  #define st_ctime                st_ctimespec.tv_sec
  #define st_ctimensec            st_ctimespec.tv_nsec
  #define st_birthtime            st_birthtimespec.tv_sec
  #define st_birthtimensec        st_birthtimespec.tv_nsec
#endif

The status information word st_flags has the following bits:

Constant	Description
`UF_NODUMP`	do not dump a file
`UF_IMMUTABLE`	file may not be changed
`UF_APPEND`	writes to file may only append
`UF_OPAQUE`	directory is opaque wrt. union
`SF_ARCHIVED`	file is archived
`SF_IMMUTABLE`	file may not be changed
`SF_APPEND`	writes to file may only append

For a description of the flags, see chflags(2).

RETURN VALUES

The stat(), lstat(), fstat(), and fstatat() functions return the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

COMPATIBILITY

Previous versions of the system used different types for the st_dev, st_uid, st_gid, st_rdev, st_size, st_blksize and st_blocks fields.

ERRORS

stat(), lstat() and fstatat() will fail if:

[EACCES]: Search permission is denied for a component of the path prefix.
[EBADF]: A badly formed vnode was encountered. This can happen if a file system information node is incorrect.
[EFAULT]: sb or path points to an invalid address.
[EIO]: An I/O error occurred while reading from or writing to the file system.
[ELOOP]: Too many symbolic links were encountered in translating the pathname.
[ENAMETOOLONG]: A component of a pathname exceeded {NAME_MAX} characters, or an entire path name exceeded {PATH_MAX} characters.
[ENOENT]: The named file does not exist.
[ENOTDIR]: A component of the path prefix is not a directory.
[ENXIO]: The named file is a character special or block special file, and the device associated with this special file does not exist.

In addition, fstatat() will fail if:

[EBADF]: path does not specify an absolute path and fd is neither AT_FDCWD nor a valid file descriptor open for reading or searching.
[ENOTDIR]: path is not an absolute path and fd is a file descriptor associated with a non-directory file.

fstat() will fail if:

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

STANDARDS

stat(), lstat(), and fstat() conform to IEEE Std 1003.1-2004 (“POSIX.1”). fstatat() conforms to IEEE Std 1003.1-2008 (“POSIX.1”).

HISTORY

The stat() and fstat() function calls appeared in Version 1 AT&T UNIX. A lstat() function call appeared in 4.2BSD.

BUGS

Applying fstat() to a socket (and thus to a pipe) returns a zero'd buffer, except for the blocksize field, and a unique device and file serial number.