giving 2 diff users access to a folder - bash

Question

I need to give access to 2 users one with read access and other with write access to a particular folder(/folder). Both the users are supposed to be in the same group(sftp)
user with read access: readsftp
user with write access: writesftp
I have done
useradd -G sftp readsftp
useradd -G sftp writesftp
Now the user writesftp should be able to write files to /folder and user readsftp should be able to only read files in the folder /folder
The vipw files read
36 sftp:x:47173:47173::/data:/bin/sh
37 ft:x:1002:1002::/home/ft:/bin/bash
38 readsftp:x:47176:47173::/data:/bin/sh
39 writeuser:x:47177:47173::/data:/bin/sh
Have I changed it rightly?
(Please observe the ID's)
Could you please help me do this by using sticky bit, and umask and chmod? In the /folder folder
I have previously changed files and folder permissions using chmod and I am unable to get through the right understanding on how to do it wrt users.
Thanks in advance.

Answer 1

First, you need to transfer the ownership of the folder (recursively) to writeftp and the group ownership to sftp:
sudo chown -R writeftp:sftp /path/to/folder
Then you enable executable permissions for the group to all folders and full permissions to the owner:
find /path/to/folder -type d -exec chmod 750 {} \;
and set read permissions for all files to the group and read/write permissions for the owner for all files:
find /path/to/folder -type f -exec chmod 640 {} \;
Following the above steps you'll solve your problem, but however, there are better solutions for your problem. You could use ACLs (access control lists) on that file system or use SELinux while the latter is much more complicated to configure and maintain.