Name

chown, fchown, lchown — change ownership of a file

Synopsis

#include <unistd.h>
int chown( const char *  path,
  uid_t   owner,
  gid_t   group);
int fchown( int   fd,
  uid_t   owner,
  gid_t   group);
int lchown( const char *  path,
  uid_t   owner,
  gid_t   group);
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
fchown(), lchown():
_BSD_SOURCE || _XOPEN_SOURCE >= 500

DESCRIPTION

These system calls change the owner and group of the file specified by path or by fd. Only a privileged process (Linux: one with the 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 CAP_CHOWN) may change the group arbitrarily.

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

When the owner or group of an executable file are changed by a non-superuser, the S_ISUID and S_ISGID mode bits are cleared. POSIX does not specify whether this also should happen when root does the chown(); the Linux behavior depends on the kernel version. In case of a non-group-executable file (i.e., one for which the S_IXGRP bit is not set) the S_ISGID bit indicates mandatory locking, and is not cleared by a chown().

RETURN VALUE

On success, zero is returned. On error, −1 is returned, and errno is set appropriately.

ERRORS

Depending on the file system, other errors can be returned. The more general errors for chown() are listed below.

EACCES

Search permission is denied on a component of the path prefix. (See also path_resolution(7).)

EFAULT

path points outside your accessible address space.

ELOOP

Too many symbolic links were encountered in resolving path.

ENAMETOOLONG

path is too long.

ENOENT

The file does not exist.

ENOMEM

Insufficient kernel memory was available.

ENOTDIR

A component of the path prefix is not a directory.

EPERM

The calling process did not have the required permissions (see above) to change owner and/or group.

EROFS

The named file resides on a read-only file system.

The general errors for fchown() are listed below:

EBADF

The descriptor is not valid.

EIO

A low-level I/O error occurred while modifying the inode.

ENOENT

See above.

EPERM

See above.

EROFS

See above.

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).

NOTES

The 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 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), chown() did not follow symbolic links. Since Linux 2.1.81, chown() does follow symbolic links, and there is a new system call lchown() that does not follow symbolic links. Since Linux 2.1.86, this new call (that has the same semantics as the old chown()) has got the same syscall number, and chown() got the newly introduced number.

EXAMPLE

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 getpwnam(3) to perform a lookup in the system password file).

#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] == '\0') {
        fprintf(stderr, "%s <owner> <file>\n", argv[0]);
        exit(EXIT_FAILURE);
    }

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

    if (*endptr != '\0') {         /* 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 */

SEE ALSO

chmod(2), fchownat(2), flock(2), path_resolution(7)

COLOPHON

This page is part of release 2.79 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


Copyright (c) 1992 Drew Eckhardt (drewcs.colorado.edu), March 28, 1992
and Copyright (c) 1998 Andries Brouwer (aebcwi.nl)
and Copyright (c) 2007 Michael Kerrisk <mtk.manpagesgmail.com>

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
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,
which is licensed free of charge, as they might when working
professionally.

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.

Modified by Michael Haardt <michaelmoria.de>
Modified 1993-07-21 by Rik Faith <faithcs.unc.edu>
Modified 1996-07-09 by Andries Brouwer <aebcwi.nl>
Modified 1996-11-06 by Eric S. Raymond <esrthyrsus.com>
Modified 1997-05-18 by Michael Haardt <michaelcantor.informatik.rwth-aachen.de>
Modified 2004-06-23 by Michael Kerrisk <mtk.manpagesgmail.com>
2007-07-08, mtk, added an example program; updated SYNOPSIS