libc/sys/stat.2

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.\"     @(#)stat.2	8.3 (Berkeley) 4/19/94
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.Dd $Mdocdate: November 21 2021 $
.Dt STAT 2
.Os
.Sh NAME
.Nm stat ,
.Nm lstat ,
.Nm fstatat ,
.Nm fstat ,
.Nm S_ISBLK ,
.Nm S_ISCHR ,
.Nm S_ISDIR ,
.Nm S_ISFIFO ,
.Nm S_ISLNK ,
.Nm S_ISREG ,
.Nm S_ISSOCK
.Nd get file status
.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 pathname leading to the file must be searchable.
.Pp
The
.Fn lstat
function is identical to
.Fn stat
except when the named file is a symbolic link,
in which case
.Fn lstat
returns information about the link itself, not the file the link references.
.Pp
The
.Fn fstatat
function is equivalent to either the
.Fn stat
or
.Fn lstat
function depending on the value of
.Fa flag
(see below), except that where
.Fa path
specifies a relative path,
the file whose information is returned is determined relative to
the directory associated with file descriptor
.Fa fd
instead of the current working directory.
.Pp
If
.Fn fstatat
is passed the special value
.Dv AT_FDCWD
(defined in
.In fcntl.h )
in the
.Fa fd
parameter, the current working directory is used
and the behavior is identical to a call to
.Fn stat
or
.Fn lstat ,
depending on whether or not the
.Dv AT_SYMLINK_NOFOLLOW
bit is set in
.Fa flag .
.Pp
The
.Fa flag
argument is the bitwise OR of zero or more of the following values:
.Pp
.Bl -tag -width AT_SYMLINK_NOFOLLOW -offset indent -compact
.It Dv AT_SYMLINK_NOFOLLOW
If
.Fa path
names a symbolic link, then the status of the symbolic link is returned.
.El
.Pp
The
.Fn fstat
function obtains the same information about an open file
known by the file descriptor
.Fa fd .
.Pp
The
.Fa sb
argument is a pointer to a
.Vt stat
structure
as defined by
.In sys/stat.h
(shown below)
and into which information is placed concerning the file.
.Bd -literal
struct stat {
    dev_t	    st_dev;	/* inode's device */
    ino_t	    st_ino;	/* inode's number */
    mode_t	    st_mode;	/* inode protection mode */
    nlink_t	    st_nlink;	/* number of hard links */
    uid_t	    st_uid;	/* user ID of the file's owner */
    gid_t	    st_gid;	/* group ID of the file's group */
    dev_t	    st_rdev;	/* device type */
    struct timespec st_atim;	/* time of last access */
    struct timespec st_mtim;	/* time of last data modification */
    struct timespec st_ctim;	/* time of last file status change */
    off_t	    st_size;	/* file size, in bytes */
    blkcnt_t	    st_blocks;	/* blocks allocated for file */
    blksize_t	    st_blksize;	/* optimal blocksize for I/O */
    u_int32_t	    st_flags;	/* user defined flags for file */
    u_int32_t	    st_gen;	/* file generation number */
};
.Ed
.Pp
The time-related fields of
.Vt struct stat
are represented in
.Vt struct timespec
format, which has nanosecond precision.
However, the actual precision is generally limited by the file
system holding the file.
The fields are as follows:
.Bl -tag -width XXXst_mtim
.It Fa st_atim
Time when file data was last accessed.
Set when the file system object was created and updated by the
.Xr utimes 2
and
.Xr read 2
system calls.
.It Fa st_mtim
Time when file data was last modified.
Changed by the
.Xr truncate 2 ,
.Xr utimes 2 ,
and
.Xr write 2
system calls.
For directories, changed by any system call that alters which files are
in the directory, such as the
.Xr unlink 2 ,
.Xr rename 2 ,
.Xr mkdir 2 ,
and
.Xr symlink 2
system calls.
.It Fa st_ctim
Time when file status was last changed (inode data modification).
Changed by the
.Xr chmod 2 ,
.Xr chown 2 ,
.Xr link 2 ,
.Xr rename 2 ,
.Xr unlink 2 ,
.Xr utimes 2 ,
and
.Xr write 2
system calls.
.El
.Pp
In addition, all the time fields are set to the current time when
a file system object is first created by the
.Xr mkdir 2 ,
.Xr mkfifo 2 ,
.Xr mknod 2 ,
.Xr open 2 ,
and
.Xr symlink 2
system calls.
.Pp
For compatibility with previous standards,
.Fa st_atime ,
.Fa st_mtime ,
and
.Fa st_ctime
macros are provided that expand to the
.Fa tv_secs
member of their respective
.Vt struct timespec
member.
Deprecated macros are also provided for some transitional names:
.Fa st_atimensec ,
.Fa st_mtimensec ,
.Fa st_ctimensec ,
.Fa st_atimespec ,
.Fa st_mtimespec ,
and
.Fa st_ctimespec .
.Pp
The size-related fields of the
.Vt struct stat
are as follows:
.Bl -tag -width XXXst_blksize
.It Fa st_blksize
The optimal I/O block size for the file.
.It Fa 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
has the following bits:
.Bd -literal -offset indent
#define S_IFMT   0170000  /* type of file mask */
#define S_IFIFO  0010000  /* named pipe (fifo) */
#define S_IFCHR  0020000  /* character special */
#define S_IFDIR  0040000  /* directory */
#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_IRWXU  0000700  /* RWX mask for owner */
#define S_IRUSR  0000400  /* R for owner */
#define S_IWUSR  0000200  /* W for owner */
#define S_IXUSR  0000100  /* X for owner */
#define S_IRWXG  0000070  /* RWX mask for group */
#define S_IRGRP  0000040  /* R for group */
#define S_IWGRP  0000020  /* W for group */
#define S_IXGRP  0000010  /* X for group */
#define S_IRWXO  0000007  /* RWX mask for other */
#define S_IROTH  0000004  /* R for other */
#define S_IWOTH  0000002  /* W for other */
#define S_IXOTH  0000001  /* X for other */
.Ed
.Pp
The following macros test a file's type.
If the file is of that type, a non-zero value is returned;
otherwise, 0 is returned.
.Bd -literal -offset indent
S_ISBLK(st_mode m)  /* block special */
S_ISCHR(st_mode m)  /* char special */
S_ISDIR(st_mode m)  /* directory */
S_ISFIFO(st_mode m) /* fifo */
S_ISLNK(st_mode m)  /* symbolic link */
S_ISREG(st_mode m)  /* regular file */
S_ISSOCK(st_mode m) /* socket */
.Ed
.Pp
For a list of access modes, see
.In sys/stat.h ,
.Xr access 2 ,
and
.Xr chmod 2 .
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
.Fn stat ,
.Fn lstat ,
and
.Fn fstatat
will fail if:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Dv NAME_MAX
characters, or an entire pathname (including the terminating NUL)
exceeded
.Dv PATH_MAX
bytes.
.It Bq Er ENOENT
A component of
.Fa path
does not exist or
.Fa path
is an empty string.
.It Bq Er EACCES
Search permission is denied for a component of the
.Fa path .
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the
.Fa path .
.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.
.El
.Pp
Additionally,
.Fn fstatat
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The value of the
.Fa flag
argument was neither zero nor
.Dv AT_SYMLINK_NOFOLLOW .
.It Bq Er EBADF
The
.Fa path
argument specifies a relative path and the
.Fa fd
argument is neither
.Dv AT_FDCWD
nor a valid file descriptor.
.It Bq Er ENOTDIR
The
.Fa path
argument specifies a relative path and the
.Fa fd
argument is a valid file descriptor but it does not reference a directory.
.It Bq Er EACCES
The
.Fa path
argument specifies a relative path but search permission is denied
for the directory which the
.Fa fd
file descriptor references.
.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 the file system.
.El
.Sh SEE ALSO
.Xr chmod 2 ,
.Xr chown 2 ,
.Xr clock_gettime 2 ,
.Xr utimes 2 ,
.Xr symlink 7
.Sh STANDARDS
Previous versions of the system used different types for the
.Fa st_dev ,
.Fa st_uid ,
.Fa st_gid ,
.Fa st_rdev ,
.Fa st_size ,
.Fa st_blksize ,
and
.Fa st_blocks
fields.
.Pp
The
.Fn fstat ,
.Fn fstatat ,
.Fn lstat ,
and
.Fn stat
functions are intended to conform to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn stat
and
.Fn fstat
system calls first appeared in
.At v1 .
The
.In sys/stat.h
header file and the
.Vt "struct stat"
were introduced in
.At v7 .
.Pp
An
.Fn lstat
function call appeared in
.Bx 4.2 .
The
.Fn fstatat
function appeared in
.Ox 5.0 .
.Sh CAVEATS
The file generation number,
.Fa st_gen ,
is only available to the superuser.
.Pp
Certain programs written when the timestamps were just of type
.Vt time_t
assumed that the members were consecutive (and could therefore
be treated as an array and have their address passed directly to
.Xr utime 3 ) .
The transition to timestamps of type
.Vt struct timespec
broke them irrevocably.
.Sh BUGS
Applying
.Fn fstat
to a pipe or socket
fails to fill in a unique device and inode number pair.
Applying
.Fn fstat
to a socket
also fails to fill in the time fields.