Group permissions ?

Good day,

curious why members of the same group can not chown/chmod files owned by the group ? 

Example:

Files are in  /tmp  and ls -ld on  /tmp  shows;
drwxrwxrwt    	2 	root     	root	4096 	Aug  3 12:16 	/tmp


These are the two files in /tmp.  Different owners, same group.

-rwxrwxr-x	1	user1	staff	499	Aug  3 12:08	df_k
-rwxrwxr-x	1	user2	staff	12579	Aug  3 12:16	ps_ef


When I execute chmod/chown I get this result;

user1@linux01#chmod 777 ps_ef
chmod: changing permissions of `ps_ef': Operation not permitted

user1@linux01#chown root:root ps_ef
chown: changing ownership of `ps_ef': Operation not permitted
user1@linux01#


Any idea's why I am unable to do this ?


Thanks for any assistance.


Maurice Miller
Xerox Office Group
Unix System Administrator