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.\"     @(#)chown.2	8.4 (Berkeley) 4/19/94
.\"
.Dd September 1, 2019
.Dt CHOWN 2
.Os
.Sh NAME
.Nm chown ,
.Nm lchown ,
.Nm fchown ,
.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 lchown "const char *path" "uid_t owner" "gid_t group"
.Ft int
.Fn fchown "int fd" "uid_t owner" "gid_t group"
.In fcntl.h
.Ft int
.Fn fchownat "int fd" "const char *path" "uid_t owner" "gid_t group" "int flag"
.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
When called to change the owner of a file,
.Fn chown ,
.Fn lchown
and
.Fn fchown
clear the set-user-id
.Dv ( S_ISUID )
bit on the file.
When a called to change the group of a file,
.Fn chown ,
.Fn lchown
and
.Fn fchown
clear the set-group-id
.Dv ( S_ISGID )
bit on the file.
These actions are taken to prevent accidental or mischievous creation of
set-user-id and set-group-id programs.
.Pp
.Fn lchown
is like
.Fn chown
except in the case where the named file is a symbolic link,
in which case
.Fn lchown
changes the owner and group of the link,
while
.Fn chown
changes the owner and group of the file the link references.
.Pp
.Fn fchown
is particularly useful when used in conjunction
with the file locking primitives (see
.Xr flock 2 ) .
.Pp
.Fn fchownat
works the same way as
.Fn chown
(or
.Fn lchown
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
One of the owner or group id's
may be left unchanged by specifying it as (uid_t)\-1 or (gid_t)\-1 respectively.
.Sh RETURN VALUES
.Rv -std chown lchown fchown fchownat
.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 EACCES
Search permission is denied for a component of the path prefix.
.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.
.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 EPERM
The effective user ID is not the super-user.
.It Bq Er EROFS
The named file resides on a read-only file system.
.El
.Pp
In addition,
.Fn fchownat
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 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 EIO
An I/O error occurred while reading from or writing to the file system.
.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.
.El
.Sh SEE ALSO
.Xr chgrp 1 ,
.Xr chmod 2 ,
.Xr flock 2 ,
.Xr symlink 7 ,
.Xr chown 8
.Sh STANDARDS
The
.Fn chown
function deviates from the semantics defined in
.St -p1003.1-90 ,
which specifies that, unless the caller is the super-user, both the
set-user-id and set-group-id bits on a file shall be cleared, regardless
of the file attribute changed.
The
.Fn lchown
and
.Fn fchown
functions, as defined by
.St -xpg4.2 ,
provide the same semantics.
.Fn fchownat
conforms to
.St -p1003.1-2008 .
.Pp
To retain conformance to these standards, compatibility interfaces
are provided by the
.Lb libposix
as follows:
.Bl -bullet -compact
.It
The
.Fn chown
function conforms to
.St -p1003.1-90
and
.St -xpg4.2 .
.It
The
.Fn lchown
and
.Fn fchown
functions conform to
.St -xpg4.2 .
.El
.Sh HISTORY
The
.Fn chown
function call appeared in
.At v1 .
The
.Fn fchown
function call appeared in
.Bx 4.2 .
.Pp
The
.Fn chown
and
.Fn fchown
functions were changed to follow symbolic links in
.Bx 4.4 .
The
.Fn lchown
function call appeared in
.Nx 1.3 .