CHOWN(3P)						     POSIX Programmer's Manual							 CHOWN(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       chown - 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  con-
       tained 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' effec-
	  tive 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 suc-
       cessful 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, respectively, 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 system.

       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 porta-
       ble 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 security 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 mandatory 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 ALSO

       chmod(), 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 Technol-
       ogy -- 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(3P)