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

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 contained in owner and group, respectively.

       Only processes with an effective user ID equal to the user ID of the file or  with  appro-
       priate  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 successful 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 correspond-
       ing 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 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 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 con-
       cerned  directly  with  security)  find	this  limitation  too  confining.  This volume of
       IEEE Std 1003.1-2001 uses may to permit secure implementations while not disallowing  Sys-
       tem V.

       System III and System V allow the owner of a file to change the group ID to anything. Ver-
       sion 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 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					 CHOWN(P)
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