lib/libsys/stat.2

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.Dd March 30, 2021
.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 * restrict path" "struct stat * restrict sb"
.Ft int
.Fn lstat "const char * restrict path" "struct stat * restrict sb"
.Ft int
.Fn fstat "int fd" "struct stat *sb"
.Ft int
.Fn fstatat "int fd" "const char *path" "struct stat *sb" "int flag"
.Sh DESCRIPTION
The
.Fn stat
system call 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
system call is like
.Fn stat
except when 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.
.Pp
The
.Fn fstat
system call obtains the same information about an open file
known by the file descriptor
.Fa fd .
.Pp
The
.Fn fstatat
system call is equivalent to
.Fn stat
and
.Fn lstat
except when the
.Fa path
specifies a relative path.
For
.Fn fstatat
and relative
.Fa path ,
the status is retrieved from a file relative to
the directory associated with the file descriptor
.Fa fd
instead of the current working directory.
.Pp
The values for the
.Fa flag
are constructed by a bitwise-inclusive OR of flags from this list,
defined in
.In fcntl.h :
.Bl -tag -width indent
.It Dv AT_SYMLINK_NOFOLLOW
If
.Fa path
names a symbolic link, the status of the symbolic link is returned.
.It Dv AT_RESOLVE_BENEATH
Only walk paths below the starting directory.
See the description of the
.Dv O_RESOLVE_BENEATH
flag in the
.Xr open 2
manual page.
.It Dv AT_EMPTY_PATH
If the
.Fa path
argument is an empty string, operate on the file or directory
referenced by the descriptor
.Fa fd .
If
.Fa fd
is equal to
.Dv AT_FDCWD ,
operate on the current working directory.
.El
.Pp
If
.Fn fstatat
is passed the special value
.Dv AT_FDCWD
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
respectively, depending on whether or not the
.Dv AT_SYMLINK_NOFOLLOW
bit is set in
.Fa flag .
.Pp
When
.Fn fstatat
is called with an absolute
.Fa path ,
it ignores the
.Fa fd
argument.
.Pp
The
.Fa sb
argument is a pointer to a
.Vt stat
structure
as defined by
.In sys/stat.h
and into which information is placed concerning the file.
.Pp
The fields of
.Vt "struct stat"
related to the file system are:
.Bl -tag -width ".Va st_nlink"
.It Va st_dev
Numeric ID of the device containing the file.
.It Va st_ino
The file's inode number.
.It Va st_nlink
Number of hard links to the file.
.It Va st_flags
Flags enabled for the file.
See
.Xr chflags 2
for the list of flags and their description.
.El
.Pp
The
.Va st_dev
and
.Va st_ino
fields together identify the file uniquely within the system.
.Pp
The time-related fields of
.Vt "struct stat"
are:
.Bl -tag -width ".Va st_birthtim"
.It Va st_atim
Time when file data was last accessed.
Changed implicitly by syscalls such as
.Xr read 2
and
.Xr readv 2 ,
and explicitly by
.Xr utimes 2 .
.It Va st_mtim
Time when file data was last modified.
Changed implicitly by syscalls such as
.Xr truncate 2 ,
.Xr write 2 ,
and
.Xr writev 2 ,
and explicitly by
.Xr utimes 2 .
Also, any syscall which modifies directory content changes the
.Va st_mtim
for the affected directory.
For instance,
.Xr creat 2 ,
.Xr mkdir 2 ,
.Xr rename 2 ,
.Xr link 2 ,
and
.Xr unlink 2 .
.It Va st_ctim
Time when file status was last changed (inode data modification).
Changed implicitly by any syscall that affects file metadata, including
.Va st_mtim ,
such as
.Xr chflags 2 ,
.Xr chmod 2 ,
.Xr chown 2 ,
.Xr truncate 2 ,
.Xr utimes 2 ,
and
.Xr write 2 .
Also, any syscall which modifies directory content changes the
.Va st_ctim
for the affected directory.
For instance,
.Xr creat 2 ,
.Xr mkdir 2 ,
.Xr rename 2 ,
.Xr link 2 ,
and
.Xr unlink 2 .
.It Va st_birthtim
Time when the inode was created.
.El
.Pp
These time-related macros are defined for compatibility:
.Bd -literal
#define	st_atime		st_atim.tv_sec
#define	st_mtime		st_mtim.tv_sec
#define	st_ctime		st_ctim.tv_sec
#ifndef _POSIX_SOURCE
#define	st_birthtime		st_birthtim.tv_sec
#endif

#ifndef _POSIX_SOURCE
#define	st_atimespec		st_atim
#define	st_mtimespec		st_mtim
#define	st_ctimespec		st_ctim
#define	st_birthtimespec	st_birthtim
#endif
.Ed
.Pp
Size-related fields of the
.Vt "struct stat"
are:
.Bl -tag -width ".Va st_blksize"
.It Va st_size
File size in bytes.
.It Va st_blksize
Optimal I/O block size for the file.
.It Va st_blocks
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 access-related fields of
.Vt "struct stat"
are:
.Bl -tag -width ".Va st_mode"
.It Va st_uid
User ID of the file's owner.
.It Va st_gid
Group ID of the file.
.It Va st_mode
Status of the file (see below).
.El
.Pp
The status information word
.Fa st_mode
has these bits:
.Bd -literal
#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_IFWHT  0160000  /* whiteout */
#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  /* read permission, owner */
#define S_IWUSR  0000200  /* write permission, owner */
#define S_IXUSR  0000100  /* execute/search permission, owner */
#define S_IRWXG  0000070  /* RWX mask for group */
#define S_IRGRP  0000040  /* read permission, group */
#define S_IWGRP  0000020  /* write permission, group */
#define S_IXGRP  0000010  /* execute/search permission, group */
#define S_IRWXO  0000007  /* RWX mask for other */
#define S_IROTH  0000004  /* read permission, other */
#define S_IWOTH  0000002  /* write permission, other */
#define S_IXOTH  0000001  /* execute/search permission, other */
.Ed
.Pp
For a list of access modes, see
.In sys/stat.h ,
.Xr access 2
and
.Xr chmod 2 .
These macros are available to test whether a
.Va st_mode
value passed in the
.Fa m
argument corresponds to a file of the specified type:
.Bl -tag -width ".Fn S_ISFIFO m"
.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_ISLNK m
Test for a symbolic link.
.It Fn S_ISREG m
Test for a regular file.
.It Fn S_ISSOCK m
Test for a socket.
.It Fn S_ISWHT m
Test for a whiteout.
.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.
.Sh RETURN VALUES
.Rv -std
.Sh COMPATIBILITY
Previous versions of the system used different types for the
.Va st_dev ,
.Va st_uid ,
.Va st_gid ,
.Va st_rdev ,
.Va st_size ,
.Va st_blksize
and
.Va st_blocks
fields.
.Sh ERRORS
The
.Fn stat
and
.Fn lstat
system calls 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 EFAULT
The
.Fa sb
or
.Fa path
argument
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 EINTEGRITY
Corrupted data was detected while reading from 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 255 characters,
or an entire path name exceeded 1023 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 EOVERFLOW
The file size in bytes cannot be
represented correctly in the structure pointed to by
.Fa sb .
.El
.Pp
The
.Fn fstat
system call will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
argument
is not a valid open file descriptor.
.It Bq Er EFAULT
The
.Fa sb
argument
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 EINTEGRITY
Corrupted data was detected while reading from the file system.
.It Bq Er EOVERFLOW
The file size in bytes cannot be
represented correctly in the structure pointed to by
.Fa sb .
.El
.Pp
In addition to the errors returned by the
.Fn lstat ,
the
.Fn fstatat
may fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa path
argument does not specify an absolute path and the
.Fa fd
argument is neither
.Dv AT_FDCWD
nor a valid file descriptor open for searching.
.It Bq Er EINVAL
The value of the
.Fa flag
argument is not valid.
.It Bq Er ENOTDIR
The
.Fa path
argument is not an absolute path and
.Fa fd
is neither
.Dv AT_FDCWD
nor a file descriptor associated with a directory.
.It Bq Er ENOTCAPABLE
.Fa path
is an absolute path,
or contained a ".." component leading to a
directory outside of the directory hierarchy specified by
.Fa fd ,
and the process is in capability mode or the
.Dv AT_RESOLVE_BENEATH
flag was specified.
.El
.Sh SEE ALSO
.Xr access 2 ,
.Xr chmod 2 ,
.Xr chown 2 ,
.Xr fhstat 2 ,
.Xr statfs 2 ,
.Xr utimes 2 ,
.Xr sticky 7 ,
.Xr symlink 7
.Sh STANDARDS
The
.Fn stat
and
.Fn fstat
system calls are expected to conform to
.St -p1003.1-90 .
The
.Fn fstatat
system call follows The Open Group Extended API Set 2 specification.
.Sh HISTORY
The
.Fn stat
and
.Fn fstat
system calls appeared in
.At v1 .
The
.Fn lstat
system call appeared in
.Bx 4.2 .
The
.Fn fstatat
system call appeared in
.Fx 8.0 .
.Sh BUGS
Applying
.Fn fstat
to a socket
returns a zeroed buffer,
except for the blocksize field,
and a unique device and inode number.