I want to make a shared ftp folder with two users that contains a file that cannot be deleted by them. /home/shared is owned by user t1 and group t1. User t2 is added to the group t1. t1 and t2's home folder is /home/shared, so now they can connect with ftp with no problems.
However as I said, there is a file that shall be only readable by them, it is called instructions.txt.
I have set the permissions this way: chmod a=r /home/shared/instructions.txt
If I "ls -l" I can see the permission is good, but they can delete the file.
I use Ubuntu desktop 13.04 and proftpd.