.\" Hey Emacs! This file is -*- nroff -*- source.
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.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
.\" and Copyright (c) 1998 Andries Brouwer (aeb@cwi.nl)
.\" and Copyright (c) 2007, 2008 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
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.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
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.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
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.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified 1993-07-21 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1996-07-09 by Andries Brouwer <aeb@cwi.nl>
.\" Modified 1996-11-06 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 1997-05-18 by Michael Haardt <michael@cantor.informatik.rwth-aachen.de>
.\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
.\" 2007-07-08, mtk, added an example program; updated SYNOPSIS
.\" 2008-05-08, mtk, Describe rules governing ownership of new files
.\"     (bsdgroups versus sysvgroups, and the effect of the parent
.\"     directory's set-group-ID permission bit).
.\"
.TH CHOWN 2 2010-09-20 "Linux" "Linux Programmer's Manual"
.SH NAME
chown, fchown, lchown \- change ownership of a file
.SH SYNOPSIS
.B #include <unistd.h>
.sp
.BI "int chown(const char *" path ", uid_t " owner ", gid_t " group );
.br
.BI "int fchown(int " fd ", uid_t " owner ", gid_t " group );
.br
.BI "int lchown(const char *" path ", uid_t " owner ", gid_t " group );
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR fchown (),
.BR lchown ():
.PD 0
.ad l
.RS 4
.TP 4
Since glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED ||
_POSIX_C_SOURCE\ >=\ 200809L
.TP
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
.RE
.ad
.PD
.SH DESCRIPTION
These system calls change the owner and group of a file.
The differ only in how the file is specified:
.IP * 2
.BR chown ()
changes the ownership of the file specified by
.IR path ,
which is dereferenced if it is a symbolic link.
.IP *
.BR fchown ()
changes the ownership of the file referred to by the open file descriptor
.IR fd .
.IP *
.BR lchown ()
is like
.BR chown (),
but does not dereference symbolic links.
.PP
Only a privileged process (Linux: one with the
.B CAP_CHOWN
capability) may change the owner of a file.
The owner of a file may change the group of the file
to any group of which that owner is a member.
A privileged process (Linux: with
.BR CAP_CHOWN )
may change the group arbitrarily.

If the
.I owner
or
.I group
is specified as \-1, then that ID is not changed.

When the owner or group of an executable file are
changed by an unprivileged user the
.B S_ISUID
and
.B S_ISGID
mode bits are cleared.
POSIX does not specify whether
this also should happen when root does the
.BR chown ();
the Linux behavior depends on the kernel version.
.\" In Linux 2.0 kernels, superuser was like everyone else
.\" In 2.2, up to 2.2.12, these bits were not cleared for superuser.
.\" Since 2.2.13, superuser is once more like everyone else.
In case of a non-group-executable file (i.e., one for which the
.B S_IXGRP
bit is not set) the
.B S_ISGID
bit indicates mandatory locking, and is not cleared by a
.BR chown ().
.SH "RETURN VALUE"
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
Depending on the file system, other errors can be returned.
The more general errors for
.BR chown ()
are listed below.
.TP
.B EACCES
Search permission is denied on a component of the path prefix.
(See also
.BR path_resolution (7).)
.TP
.B EFAULT
.I path
points outside your accessible address space.
.TP
.B ELOOP
Too many symbolic links were encountered in resolving
.IR path .
.TP
.B ENAMETOOLONG
.I path
is too long.
.TP
.B ENOENT
The file does not exist.
.TP
.B ENOMEM
Insufficient kernel memory was available.
.TP
.B ENOTDIR
A component of the path prefix is not a directory.
.TP
.B EPERM
The calling process did not have the required permissions
(see above) to change owner and/or group.
.TP
.B EROFS
The named file resides on a read-only file system.
.PP
The general errors for
.BR fchown ()
are listed below:
.TP
.B EBADF
The descriptor is not valid.
.TP
.B EIO
A low-level I/O error occurred while modifying the inode.
.TP
.B ENOENT
See above.
.TP
.B EPERM
See above.
.TP
.B EROFS
See above.
.SH "CONFORMING TO"
4.4BSD, SVr4, POSIX.1-2001.

The 4.4BSD version can only be
used by the superuser (that is, ordinary users cannot give away files).
.\" chown():
.\" SVr4 documents EINVAL, EINTR, ENOLINK and EMULTIHOP returns, but no
.\" ENOMEM.  POSIX.1 does not document ENOMEM or ELOOP error conditions.
.\" fchown():
.\" SVr4 documents additional EINVAL, EIO, EINTR, and ENOLINK
.\" error conditions.
.SH NOTES
When a new file is created (by, for example,
.BR open (2)
or
.BR mkdir (2)),
its owner is made the same as the file system user ID of the
creating process.
The group of the file depends on a range of factors,
including the type of file system,
the options used to mount the file system,
and whether or not the set-group-ID permission bit is enabled
on the parent directory.
If the file system supports the
.I "\-o\ grpid"
(or, synonymously
.IR "\-o\ bsdgroups" )
and
.I "\-o\ nogrpid"
(or, synonymously
.IR "\-o\ sysvgroups" )
.BR mount (8)
options, then the rules are as follows:
.IP * 2
If the file system is mounted with
.IR "\-o\ grpid" ,
then the group of a new file is made
the same as that of the parent directory.
.IP *
If the file system is mounted with
.IR "\-o\ nogrpid"
and the set-group-ID bit is disabled on the parent directory,
then the group of a new file is made the same as the
process's file system GID.
.IP *
If the file system is mounted with
.IR "\-o\ nogrpid"
and the set-group-ID bit is enabled on the parent directory,
then the group of a new file is made
the same as that of the parent directory.
.PP
As at Linux 2.6.25,
the
.IR "\-o\ grpid"
and
.IR "\-o\ nogrpid"
mount options are supported by ext2, ext3, ext4, and XFS.
File systems that don't support these mount options follow the
.IR "\-o\ nogrpid"
rules.
.PP
The
.BR chown ()
semantics are deliberately violated on NFS file systems
which have UID mapping enabled.
Additionally, the semantics of all system
calls which access the file contents are violated, because
.BR chown ()
may cause immediate access revocation on already open files.
Client side
caching may lead to a delay between the time where ownership have
been changed to allow access for a user and the time where the file can
actually be accessed by the user on other clients.

In versions of Linux prior to 2.1.81 (and distinct from 2.1.46),
.BR chown ()
did not follow symbolic links.
Since Linux 2.1.81,
.BR chown ()
does follow symbolic links, and there is a new system call
.BR lchown ()
that does not follow symbolic links.
Since Linux 2.1.86, this new call (that has the same semantics
as the old
.BR chown ())
has got the same syscall number, and
.BR chown ()
got the newly introduced number.
.SH EXAMPLE
.PP
The following program changes the ownership of the file named in
its second command-line argument to the value specified in its
first command-line argument.
The new owner can be specified either as a numeric user ID,
or as a username (which is converted to a user ID by using
.BR getpwnam (3)
to perform a lookup in the system password file).
.nf

#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int
main(int argc, char *argv[])
{
    uid_t uid;
    struct passwd *pwd;
    char *endptr;

    if (argc != 3 || argv[1][0] == \(aq\\0\(aq) {
        fprintf(stderr, "%s <owner> <file>\\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    uid = strtol(argv[1], &endptr, 10);  /* Allow a numeric string */

    if (*endptr != \(aq\\0\(aq) {         /* Was not pure numeric string */
        pwd = getpwnam(argv[1]);   /* Try getting UID for username */
        if (pwd == NULL) {
            perror("getpwnam");
            exit(EXIT_FAILURE);
        }

        uid = pwd\->pw_uid;
    }

    if (chown(argv[2], uid, \-1) == \-1) {
        perror("chown");
        exit(EXIT_FAILURE);
    } /* if */

    exit(EXIT_SUCCESS);
} /* main */
.fi
.SH "SEE ALSO"
.BR chmod (2),
.BR fchownat (2),
.BR flock (2),
.BR path_resolution (7),
.BR symlink (7)
.SH COLOPHON
This page is part of release 3.27 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.