Week-2 : Advanced Linux for devops

1. What Are Users & Groups?

👤 Users

Every person using the system is a user.
Each user has a User ID (UID) and a home directory.
The root user (UID 0) has full system control.

🏷️ Groups

A group is a collection of users with shared permissions.
Users belong to a primary group and can be part of multiple secondary groups.

2. User Management

✅ Create a New User

sudo useradd -m devopsuser  # Creates a user with a home directory
sudo passwd devopsuser      # Sets a password for the user

🔄 Modify a User

sudo usermod -aG docker devopsuser  # Add user to the "docker" group
sudo usermod -l newname oldname     # Rename a user
sudo usermod -d /new/home username  # Change home directory

❌ Delete a User

sudo userdel -r devopsuser  # Removes the user and their home directory

3. Groups in Linux

In Linux, groups are used to manage user permissions and access control. A group is a collection of users who share the same permissions for files, directories, or system resources.

Types of Groups in Linux

Primary Group – Each user has a primary group, which is usually created with the same name as the username. Files created by the user belong to this group by default.
Secondary (Supplementary) Group – Users can be part of multiple secondary groups, allowing them to access shared files and directories.

Common Group Commands

✅ Check your groups:

bashCopyEditgroups

✅ List all groups in the system:

bashCopyEditcat /etc/group

✅ Add a new group:

bashCopyEditsudo groupadd mygroup

✅ Add a user to a group:

bashCopyEditsudo usermod -aG mygroup username

✅ Remove a user from a group:

bashCopyEditsudo gpasswd -d username mygroup

✅ Delete a group:

bashCopyEditsudo groupdel mygroup

Why Use Groups?

🔹 Helps in managing file permissions easily
🔹 Allows multiple users to collaborate on shared files
🔹 Enhances security by restricting access

📌Task - 1 of the Linux as part of #90DaysOfDevOps Challenge.

1️⃣ User & Group Management

Learn about Linux users, groups, and permissions (/etc/passwd, /etc/group).
Task:
- Create a user devops_user and add them to a group devops_team.
- Set a password and grant sudo access.
- Restrict SSH login for certain users in /etc/ssh/sshd_config.
Task Solution:

1) Create a user devops_user and add them to a group devops_team.
- To create a user in linux, we use “useradd” command

    sudo useradd -m devops_user  ( -m : creates the users home directory)

2) Create a group devops_team

To create a group in linux, we use “groupadd” command.

    sudo groupadd devops_team

3) Add a devops_user to the devops_team group

we use the “usermod” command to add the existing user to group
- aG : Appends the user to the group without removing them from other group

sudo usermod -aG devops_team devops_user

4) set a password for a devops_user

To set password for a user, we use the “passwd” command.

sudo passwd devops-user    #( you will be promted to enter password and confirm.)

5) Grant sudo access to devops_user

we need, to edit the sudoers file to grant devops_user sudo access.

  sudo usermod -aG sudo devops_user   #(-aG sudo : add devops_user to sudo group)

6) Restrict SSH login for certain users in /etc/ssh/sshd_config.

To restrict the ssh login for certain user, we will need to modify the /etc/ssh/sshd_config file.
steps:
open the ssh configuration file
sudo vim /etc/ssh/sshd_config file.
To denu ssh access for a specific users, we need to add following line
DenyUsers user1 user2

Replace the username user1, user2 the name of user you want to deny access

for example : DenyUsers devops_user
Allow access for certain users ( if needed ) : AllowUsers devops_user
save and exit the file
Restart the ssh service for the changes to take effect
sudo systemctl restart sshd