[Linux] user & user group manage

Example

# sudo groupadd ${YOUR_GROUP_NAME}
e.g)
sudo groupadd SOME_GROUP

# sudo adduser --ingroup ${YOUR_GROUP_NAME} ${USER_NAME}
# NOTE: user name should be lower character unless you override Linux rules.
sudo adduser --ingroup SOME_GROUP some_group_some-user

Summarized Answer:

• Create a dedicated group (e.g., SOME_GROUP assign team users to this group.

• Establish a shared directory with group ownership and set the setgid bit using chmod 2770 so that new files inherit the group.

• Use specific commands to create the user some_group_some-user and assign them as the first member of the team.

Detailed Answer:

1. Group Creation:

   • Begin by creating a group for the team named SOME_GROUP using the command:

     sudo groupadd SOME_GROUP

   • This group will serve as the common owner for the shared directory and all its files.

2. User Creation and Group Assignment:

   • Create the user with the specified username and assign the user to the SOME_GROUP group. For the user some_group_some-user, execute:

     sudo adduser --ingroup SOME_GROUP some_group_some-user

   • This command creates the user and automatically adds them to the SOME_GROUP group as their primary group.

   • If the user already exists, add them to the group using:

     sudo usermod -aG SOME_GROUP some_group_some-user

3. Creating the Shared Directory:

   • Decide on a common location for the shared directory (for example, /srv/SOME_GROUP):

     sudo mkdir -p /srv/SOME_GROUP

   • Change the group ownership of this directory to the SOME_GROUP group:

     sudo chown root:SOME_GROUP /srv/SOME_GROUP

4. Understanding and Setting Permissions (chmod 2770):

   • The command chmod 2770 /srv/SOME_GROUP sets the directory permissions and is broken down as follows:

     • The first digit 2 sets the setgid (set group ID) bit. This means any new files or directories created inside /srv/SOME_GROUP will inherit the group SOME_GROUP automatically, ensuring that all team members maintain proper group ownership.

     • The next digit 7 gives the owner (here, root) read, write, and execute permissions.

     • The following digit 7 gives the group (SOME_GROUP) read, write, and execute permissions.

     • The final digit 0 denies any permissions for others (users not in the SOME_GROUP group).

   • Execute this command as follows:

     sudo chmod 2770 /srv/SOME_GROUP

5. Verifying the Configuration:

   • Use ls -ld /srv/SOME_GROUP to check that the permissions are set correctly. The output should resemble:

     drwxrws--- 2 root SOME_GROUP 4096 Apr 26 12:00 /srv/SOME_GROUP

   • The s in the group permissions field confirms that the setgid bit is active.

By following these steps, you establish a secure shared directory for the SOME_GROUP team. Users added to the SOME_GROUP group will be able to create and manage files within /srv/SOME_GROUP while automatically inheriting the proper group ownership, ensuring effective collaboration and file management within the team.