Restrict access for a RedHat user to one directory

Question

I am using RedHat Gnu/Linux I have a group of 10 users, and I'd like to restrict the access to all of them. Here are the rules I'd like to respect for them:

1. For each user user_i, there is a folder named user_i. The user_i should have writing and reading permissions on his directory and all the files/directories in it.
2. When the user_i connects to the machine, he should find himself in the user_i directory by default.
3. He (user user_i) can't see the other directories or files and has no access to them. The user_i directory is his "root" directory.

I created the group, I created all users and assigned them to this one group, and I created all folders. But I don't know how to continue beyond this.

I looked online and on this website. Most results found talk about modifying /etc/ssh/sshd_config for users connecting with SSH, while mine also needs to connect via FTP and SFTP. And other guides talk about giving access to all users of a certain group to one shared folder, which isn't my case because I need a separate folder to every user.

Edit:

Thanks everyone for your interaction and the useful information and I apologize about the confusion. Here I'll clarify the specification:

4. The user_i folders are new folders created in /transfers directory specifically for every user and named after its username. So the hierarchy looks similar to this:

   /  
   --transfers/ 
   ----user_i/ 
   ------received_data/
   ------archive_data/
   

   Every user_i will write and read data in the subfolders received_data and archive_data. He can't access any other directory, including the typical Linux directories and specifically the directories of other users (the other 9 user_i).

   By connecting to the server, he should get to user_i folder by default, and therefore only see the two subfolders received_data and archive_data.

5. All user_i belong to a group created specifically for them.

Answer 1

You are most probably looking for the ChrootDirectory option for sshd_config.

For each user user_i, there is a folder named user_i. The user_i should have writing and reading permissions on his directory and all the files/directories in it.

This is not possible with chroot. The users can not have write access to the directory they are chroot-ed in, because it would be security vulnerability (CVE-2009-2904). Every user needs its own directory inside the chroot he can write in. The filesystem hierarchy can look like this:

directory -- owner:group permissions
/chroots/ -- root:root 700
  user_i/ -- root:root 700
    data/ -- user_i:chroot_users 700

The sshd_config can look like this:

Match Group chroot_users
  ChrootDirectory /chroots/%u/

This will separate the users. But note that these users do not have any programs to run in their separated directories! You can give them only SFTP access:

Subsystem       sftp    internal-sftp

or copy the required programs into every chroot, for example for simple bash:

cp --parents /bin/bash /chroots/user_i/
cp --parents `ldd /bin/bash | cut -d'>' -f2 | awk '{print $1}'` /chroots/user_i/