Grant only selected users access to a given folder

Question

I have a linux system. And multiple users are logging into it via ssh.

So I have created multiple user accounts.

The problem I have is that some of those users need to cooperate on a given task, and in that case I would like to give a specific list of users, unlimited access to just that folder. That way they can work together in that given folder, but maintain their own setup in their home folders.

I have tried the following:
1. creating a group with the groupadd option.
2. Adding that group to all those users.
3. Changing the group of the folder they are to cooperate in to the given group.
4. Changing the rights of that folder from 755 to 775, so the given group gets write permissions.

But it doesn't work, only the owner of the folder ever gets the write permission.

How do I do achieve this?

(a very natural next question is: Make all new files in a directory accessible to a group)

Answer 1

Okay, so you have changed the group permissions correctly. However, the group ownership is wrong.

The output of ls -l currently shows the file owner and group owner of the directory to be tester, the account you created the directory with. This means that only tester can read and write to the directory.

In addition to what you have done, you will have to change the group ownership of the directory, and all files within, to that of your group, 1. See below for the solution for this particular scenario:

sudo chown -R tester:1 <folder>

The -R switch tells the command to recursively apply this ownership change to files and subdirectories within the folder (as well as the folder itself). This will retain tester as the file owner and change the group owner to 1. Alternatively you can just use 1:1 if you don't want tester involved at all.

In future, if you want to have more than the simple owner:group:everyone permissions you should look into Access Control Lists (ACLs).

Answer 2

After changing group memberships for a user (or users) you need to log out and log back in again for them to take effect. In your description above, it does not seem as if you have done that. More about this here.