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[thirdparty/man-pages.git] / man2 / chown.2

\(aq" 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 Michael Kerrisk <mtk.manpages@gmail.com>
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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
.\"
.TH CHOWN 2 2007-07-26 "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 ():
_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
.SH DESCRIPTION
.\" FIXME . The description here could be improved to explicitly say
.\" what the differences are between chown() and lchown()
These system calls change the owner and group of the file specified by
.I path
or by
.IR fd .
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 a non-superuser,
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
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)