I noticed today that my debian installation has set all the directories off of / to 755. Is this good? Any user of my system is able to FTP in and download almost anything. I'd like to change this, but I'm not sure what programs need these permissions, if any.

Also, I'm using apache and "public_html" home directories in the user accounts which have to be set to 701 for the web server to be able to view them and the files have to be at least 604, I think, but this also enables any other user to enter another user's public_html directory and download files if they know the file name. Is there a way to avoid this?

755 permission with a directory just means that non-root people can enter the directory and ls the contents. The permission of the file itself dictates whether they can read/delete/edit/execute it.

I understand how directory and file permissions work - what I'm saying is the files themselves are set to readable as well. What I don't know is if they have to be set this way for daemons and other processes to read them. For instance my /etc/passwd file is 644.

As far as the web files are concerned, they do have to be readable so that the web server can read them, but it seems this means any other user can through the file system as well.

Anyone setup for FTP, you can look into chroot.

This will jail them into whatever is their default home FTP directory, making it so they can't browse any other part of your filesystem.

The way I would do this is create a group, add the webserver user ( nobody, if you're running apache out of the box ) to that group. chgrp the files that need to be access controlled to that group. Now change permissions on the folders to 750 and files to 640. I'm assuming that the users here own their files, so they get their permissions from the 'owner' set of permissions.

Thanks, I'll try the group thing. The apache user is www-data, I think.