libc/sys/chown.2

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.\"     @(#)chown.2	8.4 (Berkeley) 4/19/94
.\" $FreeBSD: src/lib/libc/sys/chown.2,v 1.12.2.6 2001/12/14 18:34:00 ru Exp $
.\" $DragonFly: src/lib/libc/sys/chown.2,v 1.2 2003/06/17 04:26:47 dillon Exp $
.\"
.Dd August 9, 2009
.Dt CHOWN 2
.Os
.Sh NAME
.Nm chown ,
.Nm fchown ,
.Nm lchown ,
.Nm fchownat
.Nd change owner and group of a file
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn chown "const char *path" "uid_t owner" "gid_t group"
.Ft int
.Fn fchown "int fd" "uid_t owner" "gid_t group"
.Ft int
.Fn lchown "const char *path" "uid_t owner" "gid_t group"
.Ft int
.Fn fchownat "int dirfd" "const char *path" "uid_t owner" "gid_t group" "int flags"
.Sh DESCRIPTION
The owner ID and group ID of the file
named by
.Fa path
or referenced by
.Fa fd
is changed as specified by the arguments
.Fa owner
and
.Fa group .
The owner of a file may change the
.Fa group
to a group of which
he or she is a member,
but the change
.Fa owner
capability is restricted to the super-user.
.Pp
.Fn Chown
clears the set-user-id and set-group-id bits
on the file
to prevent accidental or mischievous creation of
set-user-id and set-group-id programs if not executed
by the super-user.
.Fn chown
follows symbolic links to operate on the target of the link
rather than the link itself.
.Pp
.Fn Fchown
is particularly useful when used in conjunction
with the file locking primitives (see
.Xr flock 2 ) .
.Pp
.Fn Lchown
is similar to
.Fn chown
but does not follow symbolic links.
.Pp
One of the owner or group id's
may be left unchanged by specifying it as -1.
.Pp
The
.Fn fchownat
function is equivalent to the
.Fn chown
or
.Fn lchown
functions except in the case where the
.Fa path
specifies a relative path.
In this case the file to be opened is determined relative to the directory
associated with the file descriptor
.Fa dirfd
instead of the current working directory.
If
.Fn fchownat
is passed the special value
.Dv AT_FDCWD
in the
.Fa dirfd
parameter, the current working directory is used
and the behavior is identical to a call to
.Fn chown
or
.Fn lchown .
.Pp
The values for the
.Fa flags
are constructed by a bitwise-inclusive OR of flags from the following list,
defined in
.In fcntl.h :
.Bl -tag -width indent
.It Dv AT_SYMLINK_NOFOLLOW
If
.Fa path
names a symbolic link, the mode of the symbolic link is changed.
.El
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
.Fn Chown ,
.Fn lchown
and
.Fn fchownat
will fail and the file will be unchanged if:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix or
.Fa dirfd
is not a directory.
.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 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 EPERM
The effective user ID is not the super-user.
.It Bq Er EROFS
The named file resides on a read-only file system.
.It Bq Er EFAULT
.Fa Path
points outside the process's allocated address space.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Pp
.Fn Fchown
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa fd
does not refer to a valid descriptor.
.It Bq Er EINVAL
.Fa fd
refers to a socket, not a file.
.It Bq Er EPERM
The effective user ID is not the super-user.
.It Bq Er EROFS
The named file resides on a read-only file system.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Sh SEE ALSO
.Xr chgrp 1 ,
.Xr chmod 2 ,
.Xr flock 2 ,
.Xr chown 8
.Sh STANDARDS
The
.Fn chown
function call is expected to conform to
.St -p1003.1-90 .
.Sh HISTORY
A
.Fn chown
function call appeared in
.At v7 .
The
.Fn fchown
function call
appeared in
.Bx 4.2 .
.Pp
The
.Fn chown
function was changed to follow symbolic links in
.Bx 4.4 .
The
.Fn lchown
function was added in
.Fx 3.0
to compensate for the loss of functionality.
.Pp
The
.Fn fchownat
system call appeared in
.Dx 2.3 .