-.\" Hey Emacs! This file is -*- nroff -*- source.
-.\"
.\" 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>
-.\"
-.\" 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.
+.\" and Copyright (c) 2006, 2007, 2008, 2014 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
-.\" 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-.\" manual page may be incorrect or out-of-date.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.
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified 1993-07-21 by Rik Faith <faith@cs.unc.edu>
.\" 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).
+.\" directory's set-group-ID mode bit).
.\"
-.TH CHOWN 2 2008-06-16 "Linux" "Linux Programmer's Manual"
+.TH chown 2 (date) "Linux man-pages (unreleased)"
.SH NAME
-chown, fchown, lchown \- change ownership of a file
+chown, fchown, lchown, fchownat \- change ownership of a file
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
.SH SYNOPSIS
+.nf
.B #include <unistd.h>
-.sp
-.BI "int chown(const char *" path ", uid_t " owner ", gid_t " group );
-.br
+.P
+.BI "int chown(const char *" pathname ", uid_t " owner ", gid_t " group );
.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
+.BI "int lchown(const char *" pathname ", uid_t " owner ", gid_t " group );
+.P
+.BR "#include <fcntl.h> " "/* Definition of AT_* constants */"
+.B #include <unistd.h>
+.P
+.BI "int fchownat(int " dirfd ", const char *" pathname ,
+.BI " uid_t " owner ", gid_t " group ", int " flags );
+.fi
+.P
+.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
-.in
-.sp
+.RE
+.P
.BR fchown (),
.BR lchown ():
-_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
+.nf
+ /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
+ || _XOPEN_SOURCE >= 500
+.\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
+ || /* glibc <= 2.19: */ _BSD_SOURCE
+.fi
+.P
+.BR fchownat ():
+.nf
+ Since glibc 2.10:
+ _POSIX_C_SOURCE >= 200809L
+ Before glibc 2.10:
+ _ATFILE_SOURCE
+.fi
.SH DESCRIPTION
These system calls change the owner and group of a file.
-The differ only in how the file is specified:
-.IP * 2
+The
+.BR chown (),
+.BR fchown (),
+and
+.BR lchown ()
+system calls differ only in how the file is specified:
+.IP \[bu] 3
.BR chown ()
changes the ownership of the file specified by
-.IR path ,
+.IR pathname ,
which is dereferenced if it is a symbolic link.
-.IP *
+.IP \[bu]
.BR fchown ()
changes the ownership of the file referred to by the open file descriptor
.IR fd .
-.IP *
+.IP \[bu]
.BR lchown ()
is like
.BR chown (),
but does not dereference symbolic links.
-.PP
+.P
Only a privileged process (Linux: one with the
.B CAP_CHOWN
capability) may change the owner of a file.
A privileged process (Linux: with
.BR CAP_CHOWN )
may change the group arbitrarily.
-
+.P
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
+.P
+When the owner or group of an executable file is
+changed by an unprivileged user, the
.B S_ISUID
and
.B S_ISGID
POSIX does not specify whether
this also should happen when root does the
.BR chown ();
-the Linux behavior depends on the kernel version.
+the Linux behavior depends on the kernel version,
+and since Linux 2.2.13, root is treated like other users.
.\" 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 Linux 2.2, up to Linux 2.2.12, these bits were not cleared for superuser.
+.\" Since Linux 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"
+.P
+When the owner or group of an executable file is changed (by any user),
+all capability sets for the file are cleared.
+.\"
+.SS fchownat()
+The
+.BR fchownat ()
+system call operates in exactly the same way as
+.BR chown (),
+except for the differences described here.
+.P
+If the pathname given in
+.I pathname
+is relative, then it is interpreted relative to the directory
+referred to by the file descriptor
+.I dirfd
+(rather than relative to the current working directory of
+the calling process, as is done by
+.BR chown ()
+for a relative pathname).
+.P
+If
+.I pathname
+is relative and
+.I dirfd
+is the special value
+.BR AT_FDCWD ,
+then
+.I pathname
+is interpreted relative to the current working
+directory of the calling process (like
+.BR chown ()).
+.P
+If
+.I pathname
+is absolute, then
+.I dirfd
+is ignored.
+.P
+The
+.I flags
+argument is a bit mask created by ORing together
+0 or more of the following values;
+.TP
+.BR AT_EMPTY_PATH " (since Linux 2.6.39)"
+.\" commit 65cfc6722361570bfe255698d9cd4dccaf47570d
+If
+.I pathname
+is an empty string, operate on the file referred to by
+.I dirfd
+(which may have been obtained using the
+.BR open (2)
+.B O_PATH
+flag).
+In this case,
+.I dirfd
+can refer to any type of file, not just a directory.
+If
+.I dirfd
+is
+.BR AT_FDCWD ,
+the call operates on the current working directory.
+This flag is Linux-specific; define
+.B _GNU_SOURCE
+.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
+to obtain its definition.
+.TP
+.B AT_SYMLINK_NOFOLLOW
+If
+.I pathname
+is a symbolic link, do not dereference it:
+instead operate on the link itself, like
+.BR lchown ().
+(By default,
+.BR fchownat ()
+dereferences symbolic links, like
+.BR chown ().)
+.P
+See
+.BR openat (2)
+for an explanation of the need for
+.BR fchownat ().
+.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
.I errno
-is set appropriately.
+is set to indicate the error.
.SH ERRORS
-Depending on the file system, other errors can be returned.
+Depending on the filesystem,
+errors other than those listed below can be returned.
+.P
The more general errors for
.BR chown ()
are listed below.
(See also
.BR path_resolution (7).)
.TP
+.B EBADF
+.RB ( fchown ())
+.I fd
+is not a valid open file descriptor.
+.TP
+.B EBADF
+.RB ( fchownat ())
+.I pathname
+is relative but
+.I dirfd
+is neither
+.B AT_FDCWD
+nor a valid file descriptor.
+.TP
.B EFAULT
-.I path
+.I pathname
points outside your accessible address space.
.TP
+.B EINVAL
+.RB ( fchownat ())
+Invalid flag specified in
+.IR flags .
+.TP
+.B EIO
+.RB ( fchown ())
+A low-level I/O error occurred while modifying the inode.
+.TP
.B ELOOP
Too many symbolic links were encountered in resolving
-.IR path .
+.IR pathname .
.TP
.B ENAMETOOLONG
-.I path
+.I pathname
is too long.
.TP
.B ENOENT
.B ENOTDIR
A component of the path prefix is not a directory.
.TP
+.B ENOTDIR
+.RB ( fchownat ())
+.I pathname
+is relative and
+.I dirfd
+is a file descriptor referring to a file other than 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.
+The file is marked immutable or append-only.
+(See
+.BR ioctl_iflags (2).)
.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).
+The named file resides on a read-only filesystem.
+.SH VERSIONS
+The 4.4BSD version can be
+used only 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 STANDARDS
+POSIX.1-2008.
+.SH HISTORY
+.TP
+.BR chown ()
+.TQ
+.BR fchown ()
+.TQ
+.BR lchown ()
+4.4BSD, SVr4, POSIX.1-2001.
+.TP
+.BR fchownat ()
+POSIX.1-2008.
+Linux 2.6.16,
+glibc 2.4.
.SH NOTES
+.SS Ownership of new files
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
+its owner is made the same as the filesystem 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
+including the type of filesystem,
+the options used to mount the filesystem,
+and whether or not the set-group-ID mode bit is enabled
on the parent directory.
-If the file system supports the
-.I "\-o\ grpid"
+If the filesystem supports the
+.B "\-o\ grpid"
(or, synonymously
-.IR "\-o\ bsdgroups" )
+.BR "\-o\ bsdgroups" )
and
-.I "\-o\ nogrpid"
+.B "\-o\ nogrpid"
(or, synonymously
-.IR "\-o\ sysvgroups" )
+.BR "\-o\ sysvgroups" )
.BR mount (8)
options, then the rules are as follows:
-.IP * 2
-If the file system is mounted with
-.IR "\-o\ grpid" ,
+.IP \[bu] 3
+If the filesystem is mounted with
+.BR "\-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"
+.IP \[bu]
+If the filesystem is mounted with
+.B \-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"
+process's filesystem GID.
+.IP \[bu]
+If the filesystem is mounted with
+.B \-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,
+.P
+As at Linux 4.12,
the
-.IR "\-o\ grpid"
+.B \-o\ grpid
and
-.IR "\-o\ nogrpid"
+.B \-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"
+Filesystems that don't support these mount options follow the
+.B \-o\ nogrpid
rules.
-.PP
+.SS glibc notes
+On older kernels where
+.BR fchownat ()
+is unavailable, the glibc wrapper function falls back to the use of
+.BR chown ()
+and
+.BR lchown ().
+When
+.I pathname
+is a relative pathname,
+glibc constructs a pathname based on the symbolic link in
+.I /proc/self/fd
+that corresponds to the
+.I dirfd
+argument.
+.SS NFS
The
.BR chown ()
-semantics are deliberately violated on NFS file systems
+semantics are deliberately violated on NFS filesystems
which have UID mapping enabled.
Additionally, the semantics of all system
calls which access the file contents are violated, because
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),
+.SS Historical details
+The original Linux
+.BR chown (),
+.BR fchown (),
+and
+.BR lchown ()
+system calls supported only 16-bit user and group IDs.
+Subsequently, Linux 2.4 added
+.BR chown32 (),
+.BR fchown32 (),
+and
+.BR lchown32 (),
+supporting 32-bit IDs.
+The glibc
+.BR chown (),
+.BR fchown (),
+and
+.BR lchown ()
+wrapper functions transparently deal with the variations across kernel versions.
+.P
+Before Linux 2.1.81 (except 2.1.46),
.BR chown ()
did not follow symbolic links.
Since Linux 2.1.81,
has got the same syscall number, and
.BR chown ()
got the newly introduced number.
-.SH EXAMPLE
-.PP
+.SH EXAMPLES
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.
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
-
+.SS Program source
+.\" SRC BEGIN (chown.c)
+.EX
#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]);
+ char *endptr;
+ uid_t uid;
+ struct passwd *pwd;
+\&
+ if (argc != 3 || argv[1][0] == \[aq]\e0\[aq]) {
+ fprintf(stderr, "%s <owner> <file>\en", 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 */
+\&
+ if (*endptr != \[aq]\e0\[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"
+}
+.EE
+.\" SRC END
+.SH SEE ALSO
+.BR chgrp (1),
+.BR chown (1),
.BR chmod (2),
-.BR fchownat (2),
.BR flock (2),
.BR path_resolution (7),
.BR symlink (7)
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