[root@bofh /]# install -d /tmp/xxx -g bin -m 6775 [root@bofh /]# ls -ld /tmp/xxx drwxrwxr-x 2 root root 1024 Mar 9 02:17 /tmp/xxx [root@bofh /]# install -d /tmp/xxx -g bin -m 6775 [root@bofh /]# ls -ld /tmp/xxx drwsrwsr-x 2 root bin 1024 Mar 9 02:17 /tmp/xxx Install is likely first doing the chmod() call and only then the chown() call instead of the other way around.
Fixed.