CHOWN(P) POSIX Programmer's Manual CHOWN(P)NAMEchown - change owner and group of a file
SYNOPSIS
#include <unistd.h>
int chown(const char *path, uid_t owner, gid_t group);
DESCRIPTION
The chown() function shall change the user and group ownership of a
file.
The path argument points to a pathname naming a file. The user ID and
group ID of the named file shall be set to the numeric values contained
in owner and group, respectively.
Only processes with an effective user ID equal to the user ID of the
file or with appropriate privileges may change the ownership of a file.
If _POSIX_CHOWN_RESTRICTED is in effect for path:
* Changing the user ID is restricted to processes with appropriate
privileges.
* Changing the group ID is permitted to a process with an effective
user ID equal to the user ID of the file, but without appropriate
privileges, if and only if owner is equal to the file's user ID or (
uid_t)-1 and group is equal either to the calling process' effective
group ID or to one of its supplementary group IDs.
If the specified file is a regular file, one or more of the S_IXUSR,
S_IXGRP, or S_IXOTH bits of the file mode are set, and the process does
not have appropriate privileges, the set-user-ID (S_ISUID) and set-
group-ID (S_ISGID) bits of the file mode shall be cleared upon success‐
ful return from chown(). If the specified file is a regular file, one
or more of the S_IXUSR, S_IXGRP, or S_IXOTH bits of the file mode are
set, and the process has appropriate privileges, it is implementation-
defined whether the set-user-ID and set-group-ID bits are altered. If
the chown() function is successfully invoked on a file that is not a
regular file and one or more of the S_IXUSR, S_IXGRP, or S_IXOTH bits
of the file mode are set, the set-user-ID and set-group-ID bits may be
cleared.
If owner or group is specified as ( uid_t)-1 or ( gid_t)-1, respec‐
tively, the corresponding ID of the file shall not be changed. If both
owner and group are -1, the times need not be updated.
Upon successful completion, chown() shall mark for update the st_ctime
field of the file.
RETURN VALUE
Upon successful completion, 0 shall be returned; otherwise, -1 shall be
returned and errno set to indicate the error. If -1 is returned, no
changes are made in the user ID and group ID of the file.
ERRORS
The chown() function shall fail if:
EACCES Search permission is denied on a component of the path prefix.
ELOOP A loop exists in symbolic links encountered during resolution of
the path argument.
ENAMETOOLONG
The length of the path argument exceeds {PATH_MAX} or a pathname
component is longer than {NAME_MAX}.
ENOTDIR
A component of the path prefix is not a directory.
ENOENT A component of path does not name an existing file or path is an
empty string.
EPERM The effective user ID does not match the owner of the file, or
the calling process does not have appropriate privileges and
_POSIX_CHOWN_RESTRICTED indicates that such privilege is
required.
EROFS The named file resides on a read-only file system.
The chown() function may fail if:
EIO An I/O error occurred while reading or writing to the file sys‐
tem.
EINTR The chown() function was interrupted by a signal which was
caught.
EINVAL The owner or group ID supplied is not a value supported by the
implementation.
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
resolution of the path argument.
ENAMETOOLONG
As a result of encountering a symbolic link in resolution of the
path argument, the length of the substituted pathname string
exceeded {PATH_MAX}.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
Although chown() can be used on some implementations by the file owner
to change the owner and group to any desired values, the only portable
use of this function is to change the group of a file to the effective
GID of the calling process or to a member of its group set.
RATIONALE
System III and System V allow a user to give away files; that is, the
owner of a file may change its user ID to anything. This is a serious
problem for implementations that are intended to meet government secu‐
rity regulations. Version 7 and 4.3 BSD permit only the superuser to
change the user ID of a file. Some government agencies (usually not
ones concerned directly with security) find this limitation too confin‐
ing. This volume of IEEE Std 1003.1-2001 uses may to permit secure
implementations while not disallowing System V.
System III and System V allow the owner of a file to change the group
ID to anything. Version 7 permits only the superuser to change the
group ID of a file. 4.3 BSD permits the owner to change the group ID of
a file to its effective group ID or to any of the groups in the list of
supplementary group IDs, but to no others.
The POSIX.1-1990 standard requires that the chown() function invoked by
a non-appropriate privileged process clear the S_ISGID and the S_ISUID
bits for regular files, and permits them to be cleared for other types
of files. This is so that changes in accessibility do not accidentally
cause files to become security holes. Unfortunately, requiring these
bits to be cleared on non-executable data files also clears the manda‐
tory file locking bit (shared with S_ISGID), which is an extension on
many implementations (it first appeared in System V). These bits should
only be required to be cleared on regular files that have one or more
of their execute bits set.
FUTURE DIRECTIONS
None.
SEE ALSOchmod() , pathconf() , the Base Definitions volume of
IEEE Std 1003.1-2001, <sys/types.h>, <unistd.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 CHOWN(P)
