Creating Users and Groups, Setting Access Rights, Managing Processes

1. Problem statement

Alright, we've got some intense hands-on work ahead, where you'll be able to apply all the knowledge from the previous lectures. We'll be creating users, grouping them, setting up unique access permissions, and managing processes in the system. And if you're wondering, "Why do I even need all this?", imagine you're a system administrator or a DevOps engineer, and you're tasked with configuring a server for team collaboration. Or maybe you're just trying to save your computer from chaos! In the real world, situations like this happen all the time.

Your goal is to set up the system for the following users and processes:

1. Create two users: user1 and user2. They'll be collaborating in the developers group.
2. Configure a file (for example, project.txt) so that only members of the developers group can edit it.
3. Create a few processes (for instance, using the sleep command) and learn how to terminate them if necessary.
4. View active processes to determine which ones are consuming the most resources.

Sounds like a plan? Let's make it happen step by step.

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2. Step 1: Creating Users

1. Creating Users

First, let's create two users:

sudo adduser user1
sudo adduser user2

When you run these commands, the system will ask you to set a password and provide a description for each user. We won't fill in unnecessary details here, you can just press Enter.

Each user automatically gets a home directory in /home. You can check it with:

ls /home

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3. Step 2: Creating a Group and Adding Users

1. Creating a Group

To let users collaborate on projects, let's add them to a group. First, we'll create a group called developers:

sudo groupadd developers

2. Adding Users to the Group

Now, let's add users user1 and user2 to the developers group. We'll use the usermod command for this:

sudo usermod -aG developers user1
sudo usermod -aG developers user2

3. Checking Group Membership

To make sure the users were added to the group correctly, run:

groups user1
groups user2

You should see that user1 and user2 are members of the developers group.

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4. Step 3: Working with Files and Permissions

1. Creating a File for the Project

Let's create a file project.txt in the home directory of one of the users (e.g., user1):

sudo -u user1 touch /home/user1/project.txt

The sudo -u command lets us perform actions on behalf of another user.

2. Changing File Owner and Group

We'll assign user1 as the owner, and the group as developers, so both users have the same access permissions:

sudo chown user1:developers /home/user1/project.txt

3. Setting File Permissions

Now, let's change the file permissions. We'll use the chmod command:

sudo chmod 660 /home/user1/project.txt

What did we do? We gave the owner user1 and the group developers read and write permissions rw-, while everyone else has no access.

You can check the file permissions with the ls command:

ls -l /home/user1/project.txt

Expected output:

-rw-rw---- 1 user1 developers 0 date time /home/user1/project.txt

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5. Step 4: Running Processes

1. Running Processes

For practice, let's create a couple of "long-living" processes using the sleep command:

sleep 300 &
sleep 400 &
sleep 500 &

Each sleep command runs in the background thanks to the & symbol.

To check the list of processes, use the command ps:

ps

You can see more info using ps aux:

ps aux | grep sleep

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6. Step 5: Terminating Processes

1. Killing a process by PID

Identify the PID of one of the processes (for example, sleep) and terminate it:

kill PID

Where PID is the process identifier, which can be found using ps.

2. Killing a process by name

If you want to kill all sleep processes, use the killall command:

killall sleep

3. Using pkill

If you don't remember the exact process name, pkill can help terminate the process by partial name match:

pkill slee

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7. Step 6: Monitoring Processes

To monitor system load, use:

1. top — for real-time monitoring:

      top
   

   Here you can check CPU load, memory usage, and active processes. Use the k key combination to terminate a process directly from the interface.

2. htop — more user-friendly interface (if you have it installed):

   htop
   

   To exit, press F10.

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8. Checklist

After completing all the steps, you should make sure that:

1. Two users user1 and user2 are created.
2. A group developers is created and configured, and both users are added to it.
3. A file project.txt is created and is accessible only to the developers group.
4. Several processes are created and terminated using commands like kill, killall, and pkill.
5. You successfully checked the list of processes using ps, top, or htop.

If everything is done — congrats! You've gone through all the key stages of user, group, access rights, and process management in a Linux system. May the console power be with you!