change permissions of folder to group sudo read/write and all users only read

Question

How can i change the permissions of directory public to all users only read and only sudo users (group members of sudo) to only read/write access.

I prefer to do it like this :

chown root:sudo ~/public

Answer 1

chmod and chgrp are the tools needed here:

# make the group 'sudo' the owner of the directory 'public'
chgrp sudo public
give the group read/write access and others just read access
chmod g=rwx,o=rx public

Result:

ls -ld public
drwxrwxr-x 2 pduck sudo 4096 Feb  4 14:08 public

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Update

If you also want to prevent the current owner pduck from accessing the directory (regardless of his membership), then give the ownership to root:

sudo chown root:sudo public
sudo chmod 0750 public
result:
drwxrwxr-x 2 root sudo 4096 Feb 28 11:32 public 

Now only root and members of the sudo group have read/write access. But root can access the directory anyway, even when he's not the owner, so this is safe.

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The first thought might be to keep the ownership and just reduce the rights:

sudo chown pduck:sudo public
sudo chmod 0050 public
gives
d---r-x--- 2 pduck sudo 4096 Feb 28 11:32 public 

Now – although the owner – pduck cannot access the directory. But (as owner) he can simply regain access by issuing chmod u+rwx public himself, so this is not safe.