How to allow members of a group to change file permissions on linux

Only the owner of a file or root is permitted to change permissions in Linux (write access != permission change access)

The only way I can think of is using sudo. I don't know if that would do the trick, and I'd be exceedingly cautious about how you specify the sudo rules so that the users don't have any additional privileges.

Note that if they are connecting using an FTP server, sudo probably won't be the answer.

One solution (which I've had to use) is a cron job going through and changing the permissions of a specified directory and files under it. Not pretty but it works.

If you want to extend the ability of users to change this, you might consider allowing the users from the ftpgroup to allow chmod within the specified directory with an appropriate rule using sudo.

Or you can make a shell script which does the appropriate checks and does the function, and make that program allowed to be run via sudo. I do not suggest nor recommend a set-uid shell script.

Just give the 'ftpusers' write permissions and ownership on that directory:

chgrp ftpusers <directory>
chmod g+rwx <directory>

And then set the GID bit so all new files inherit group ownership:

chmod g+s <directory>