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Mention the word 'inode' next to st_ino so it's easier to find.
Bump date.

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.\"     @(#)stat.2	8.4 (Berkeley) 5/1/95
.\"
.Dd April 10, 2014
.Dt STAT 2
.Os
.Sh NAME
.Nm stat ,
.Nm lstat ,
.Nm fstat ,
.Nm fstatat ,
.Nd get file status
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/stat.h
.Ft int
.Fn stat "const char *path" "struct stat *sb"
.Ft int
.Fn lstat "const char *path" "struct stat *sb"
.Ft int
.Fn fstat "int fd" "struct stat *sb"
.In sys/stat.h
.In fcntl.h
.Ft int
.Fn fstatat "int fd" "const char *path" "struct stat *sb" "int flag"
.Sh DESCRIPTION
The
.Fn stat
function obtains information about the file pointed to by
.Fa 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.
.Pp
The function
.Fn lstat
is like
.Fn stat
except in the case where the named file is a symbolic link,
in which case
.Fn lstat
returns information about the link,
while
.Fn stat
returns information about the file the link references.
The
.Fn fstat
function obtains the same information about an open file
known by the file descriptor
.Fa fd .
.Pp
.Fn fstatat
works the same way as
.Fn stat
(or
.Fn lstat
if
.Dv AT_SYMLINK_NOFOLLOW
is set in
.Fa flag )
except if
.Fa path
is relative.
In that case, it is looked up from a directory whose file
descriptor was passed as
.Fa fd .
Search permission is required on this directory.
.\"    (These alternatives await a decision about the semantics of O_SEARCH)
.\" Search permission is required on this directory
.\" except if
.\" .Fa fd
.\" was opened with the
.\" .Dv O_SEARCH
.\" flag.
.\"    - or -
.\" This file descriptor must have been opened with the
.\" .Dv O_SEARCH
.\" flag.
.Fa fd
can be set to
.Dv AT_FDCWD
in order to specify the current directory.
.Pp
The
.Fa sb
argument is a pointer to a
.Fa stat
structure
as defined by
.In sys/stat.h
and into which information is placed concerning the file.
.Ss The Standard Structure
The following standards-compliant fields are defined in the structure:
.Bl -column -offset indent \
"nlink_t " "st_nlink " "Description"
.It Sy Type Ta Sy Entry Ta Sy Description
.It Vt dev_t Ta st_dev Ta device ID containing the file
.It Vt ino_t Ta st_ino Ta serial number of the file (inode number)
.It Vt mode_t Ta st_mode Ta mode of the file
.It Vt nlink_t Ta st_nlink Ta number of hard links to the file
.It Vt uid_t Ta st_uid Ta user ID of the owner
.It Vt gid_t Ta st_gid Ta group ID of the owner
.It Vt dev_t Ta st_rdev Ta device type (character or block special)
.It Vt off_t Ta st_size Ta size of the file in bytes
.It Vt time_t Ta st_atime Ta time of last access
.It Vt time_t Ta st_mtime Ta time of last data modification
.It Vt time_t Ta st_ctime Ta  time of last file status change
.It Vt blksize_t Ta st_blksize Ta preferred I/O block size (fs-specific)
.It Vt blkcnt_t Ta st_blocks Ta blocks allocated for the file
.El
.Pp
These are specified in the
.St -p1003.1-2004
standard.
The
.Va st_ino
and
.Va st_dev
fields taken together uniquely identify the file within the system.
Most of the types are defined in
.Xr types 3 .
.Pp
The time-related fields are:
.Bl -tag -width st_blksize -offset indent
.It Va st_atime
Time when file data was last accessed.
Changed by the
.Xr mknod 2 ,
.Xr utimes 2 ,
and
.Xr read 2
system calls.
.It Va st_mtime
Time when file data was last modified.
Changed by the
.Xr mknod 2 ,
.Xr utimes 2 ,
and
.Xr write 2
system calls.
.It Va st_ctime
Time when file status was last changed (file metadata modification).
Changed by the
.Xr chflags 2 ,
.Xr chmod 2 ,
.Xr chown 2 ,
.Xr link 2 ,
.Xr mknod 2 ,
.Xr rename 2 ,
.Xr unlink 2 ,
.Xr utimes 2 ,
and
.Xr write 2
system calls.
.El
.Pp
The size-related fields of the
.Fa struct stat
are as follows:
.Bl -tag -width st_blksize -offset indent
.It Va 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.
.It Va st_blksize
The optimal I/O block size for the file.
.It Va 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.
.El
.Pp
The status information word
.Fa st_mode
contains bits that define the access mode (see
.Xr chmod 2 )
and the type (see
.Xr dirent 3 )
of the file.
The following macros can be used to test
whether a file is of the specified type.
The value
.Fa m
supplied to the macros is the value of
.Va st_mode .
.Bl -tag -width "S_ISSOCK(m)" -offset indent
.It Fn S_ISBLK "m"
Test for a block special file.
.It Fn S_ISCHR "m"
Test for a character special file.
.It Fn S_ISDIR "m"
Test for a directory.
.It Fn S_ISFIFO "m"
Test for a pipe or FIFO special file.
.It Fn S_ISREG "m"
Test for a regular file.
.It Fn S_ISLNK "m"
Test for a symbolic link.
.It Fn S_ISSOCK "m"
Test for a socket.
.El
.Pp
The macros evaluate to a non-zero value if the test
is true or to the value 0 if the test is false.
.Ss NetBSD Extensions
The following additional
.Nx
specific fields are present:
.Bl -column -offset indent \
"uint32_t" "st_birthtimensec" "Description"
.It Sy Type Ta Sy Entry Ta Sy Description
.It Vt long Ta st_atimensec Ta last access (nanoseconds)
.It Vt long Ta st_mtimensec Ta last modification (nanoseconds)
.It Vt long Ta st_ctimensec Ta last status change (nanoseconds)
.It Vt time_t Ta st_birthtime Ta time of inode creation
.It Vt long Ta st_birthtimensec Ta inode creation (nanoseconds)
.It Vt uint32_t Ta st_flags Ta user defined flags for the file
.It Vt uint32_t Ta st_gen Ta file generation number
.\"
.\" XXX: What is this?
.\"
.It Vt uint32_t Ta st_spare[2] Ta implementation detail
.El
.Pp
However, if
_NETBSD_SOURCE
is furthermore defined, instead of the above,
the following are present in the structure:
.Bl -column -offset indent \
"struct timespec " "st_birthtimensec" "Description"
.It Sy Type Ta Sy Entry Ta Sy Description
.It Vt struct timespec Ta st_atimespec Ta time of last access
.It Vt struct timespec Ta st_mtimespec Ta time of last modification
.It Vt struct timespec Ta st_birthtimespec Ta time of creation
.It Vt uint32_t Ta st_flags Ta user defined flags
.It Vt uint32_t Ta st_gen Ta file generation number
.\"
.\" XXX: What is this?
.\"
.It Vt uint32_t Ta st_spare[2] Ta implementation detail
.El
.Pp
In this case the following macros are provided for convenience:
.Bd -literal -offset indent
#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
.Ed
.Pp
The status information word
.Fa st_flags
has the following bits:
.Bl -column -offset indent \
"struct timespec " "st_birthtimensec"
.It Sy Constant Ta Sy Description
.It Dv UF_NODUMP Ta do not dump a file
.It Dv UF_IMMUTABLE Ta file may not be changed
.It Dv UF_APPEND Ta writes to file may only append
.It Dv UF_OPAQUE Ta directory is opaque wrt. union
.It Dv SF_ARCHIVED Ta file is archived
.It Dv SF_IMMUTABLE Ta file may not be changed
.It Dv SF_APPEND Ta writes to file may only append
.El
.Pp
For a description of the flags, see
.Xr chflags 2 .
.Sh RETURN VALUES
.Rv -std stat lstat fstat fstatat
.Sh COMPATIBILITY
Previous versions of the system used different types for the
.Li st_dev ,
.Li st_uid ,
.Li st_gid ,
.Li st_rdev ,
.Li st_size ,
.Li st_blksize
and
.Li st_blocks
fields.
.Sh ERRORS
.Fn stat ,
.Fn lstat
and
.Fn fstatat
will fail if:
.Bl -tag -width Er
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.It Bq Er EBADF
A badly formed vnode was encountered.
This can happen if a file system information node is incorrect.
.It Bq Er EFAULT
.Fa sb
or
.Fa path
points to an invalid address.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Brq Dv NAME_MAX
characters, or an entire path name exceeded
.Brq Dv PATH_MAX
characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENXIO
The named file is a character special or block
special file, and the device associated with this special file
does not exist.
.El
.Pp
In addition,
.Fn fstatat
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa path
does not specify an absolute path and
.Fa fd
is neither
.Dv AT_FDCWD
nor a valid file descriptor open for reading or searching.
.It Bq Er ENOTDIR
.Fa path
is not an absolute path and
.Fa fd
is a file descriptor associated with a non-directory file.
.El
.Pp
.Fn fstat
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa fd
is not a valid open file descriptor.
.It Bq Er EFAULT
.Fa sb
points to an invalid address.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Sh SEE ALSO
.Xr chflags 2 ,
.Xr chmod 2 ,
.Xr chown 2 ,
.Xr utimes 2 ,
.Xr dirent 3 ,
.Xr types 3 ,
.Xr symlink 7
.Sh STANDARDS
.Fn stat ,
.Fn lstat ,
and
.Fn fstat
conform to
.St -p1003.1-2004 .
.Fn fstatat
conforms to
.St -p1003.1-2008 .
.Sh HISTORY
A
.Fn stat
function call appeared in
.At v2 .
A
.Fn lstat
function call appeared in
.Bx 4.2 .
.Sh BUGS
Applying
.Fn 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.