Managing Users and Groups

Welcome to managing users and groups on Linux! This lesson is crucial for server administration, security, and organizing who can do what.

Every action on a Linux server is performed by a user. Users are organized into groups to simplify permissions and access control.

A user account is your digital identity on a Linux system. It defines your home directory, shell, and what files and commands you can access.

• Each user has a unique username.
• Users log in with a password (or SSH key).
• Accounts isolate user activities, enhancing security.

The primary command to create a new user account is useradd. By default, it creates a new user, a home directory, and assigns a default shell.

You'll need sudo (superuser do) privileges to run this command, as it modifies system settings.

After creating a user, they won't be able to log in until you set a password for them. The passwd command is used for this.

You'll be prompted to enter the new password twice. Remember to choose strong, unique passwords!

Behind every username, Linux uses a unique number called a User ID (UID). This is how the system truly identifies users.

• UID 0 is always for the root user.
• UIDs 1-999 are typically reserved for system accounts.
• Regular user accounts usually start from UID 1000.

You can see a user's UID with the id command.

Need to change a user's home directory, login shell, or username? The usermod command is your tool.

• -d: Change home directory.
• -s: Change login shell.
• -l: Change username.

Always use sudo with usermod.

When a user no longer needs access, you can remove their account using userdel. It's important to decide if you want to keep or remove their home directory.

• userdel username: Deletes the user account, but keeps their home directory and mail spool.
• userdel -r username: Deletes the user account and removes their home directory and mail spool.

Groups allow you to manage permissions for multiple users at once. Instead of setting permissions for each individual, you set them for a group, and then add users to that group.

• Every user belongs to at least one primary group.
• Users can also belong to multiple supplementary groups.

Just like users, groups have commands for creation, deletion, and management:

• groupadd groupname: Creates a new group.
• groupdel groupname: Deletes an existing group.
• gpasswd -a user group: Adds a user to a supplementary group.
• gpasswd -d user group: Removes a user from a group.

The sudo command allows regular users to execute commands with root (administrator) privileges. This is safer than logging in as root directly.

To grant a user sudo access, you typically add them to a special group, often named sudo (on Debian/Ubuntu) or wheel (on Red Hat/CentOS).

Which command would you use to remove a user named olduser AND delete their home directory?

Great job! You've learned the essentials of managing users and groups on a Linux server:

• Use useradd and passwd to create new users.
• usermod helps modify user properties.
• userdel removes user accounts.
• groupadd, groupdel, and gpasswd manage groups.
• Grant sudo privileges by adding users to the appropriate group.

Understanding these commands is fundamental for secure and organized server administration.