libc/sys/stat.2

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.\"     @(#)stat.2	8.3 (Berkeley) 4/19/94
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.Dd April 19, 1994
.Dt STAT 2
.Os
.Sh NAME
.Nm stat ,
.Nm lstat ,
.Nm fstat
.Nd get file status
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <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"
.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
.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.
Unlike other file system objects,
symbolic links do not have an owner, group, access mode, times, etc.
Instead, these attributes are taken from the directory that
contains the link.
The only attributes returned from an
.Fn lstat
that refer to the symbolic link itself are the file type
.Pq Dv S_IFLNK ,
size, blocks, and link count (always 1).
.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
.Fn stat
structure
as defined by
.Aq Pa sys/stat.h
(shown below)
and into which information is placed concerning the file.
.Bd -literal
struct stat {
    dev_t      st_dev;    /* device inode resides on */
    ino_t      st_ino;    /* inode's number */
    mode_t     st_mode;   /* inode's mode */
    nlink_t    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;   /* device type, for special file inode */
    struct timespec st_atimespec;  /* time of last access */
    struct timespec st_mtimespec;  /* time of last data modification */
    struct timespec st_ctimespec;  /* time of last file status change */
    off_t      st_size;   /* file size, in bytes */
    int64_t    st_blocks; /* blocks allocated for file */
    u_int32_t  st_blksize;/* optimal file sys I/O ops blocksize */
    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
.Li struct stat
are as follows:
.Bl -tag -width XXXst_mtime
.It Fa 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 Fa 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 Fa st_ctime
Time when file status was last changed (inode data modification).
Changed by the
.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
.Li 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
#define S_IFMT   0170000  /* type of file */
#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_IRUSR  0000400  /* read permission, owner */
#define S_IWUSR  0000200  /* write permission, owner */
#define S_IXUSR  0000100  /* execute/search permission, owner */
.Ed
.Pp
For a list of access modes, see
.Aq Pa sys/stat.h ,
.Xr access 2 ,
and
.Xr chmod 2 .
.Sh RETURN VALUES
Upon successful completion a value of 0 is returned.
Otherwise, a value of \-1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn stat
and
.Fn lstat
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 path name exceeded
.Dv PATH_MAX
characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EFAULT
.Fa sb
or
.Em name
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
.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 chmod 2 ,
.Xr chown 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 stat
and
.Fn fstat
function calls are expected to conform to
.St -p1003.1-88 .
.Sh HISTORY
A
.Fn stat
function appeared in
.At v2 .
An
.Fn lstat
function call appeared in
.Bx 4.2 .
.Sh CAVEATS
The file generation number,
.Fa st_gen ,
is only available to the superuser.
.Pp
The fields in the stat structure currently marked
.Fa st_spare1 ,
.Fa st_spare2 ,
and
.Fa 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
.Xr utimes 2 ) .
.Sh BUGS
Applying
.Fn 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.