Creating/Deleting Users

Absolutely! Let’s dive into user management in Ubuntu, breaking down each command used for viewing, creating, modifying, and deleting users. Here’s everything you need as a newcomer to Linux and Ubuntu.

1. Commands to View Existing Users in Ubuntu

• /etc/passwd File:

  • The /etc/passwd file contains a list of all users on the system. Each line in this file represents a single user, including the root user and any system or application users created during system setup.

  • To view this file, use the command:

    cat /etc/passwd

  • Each entry in /etc/passwd has several fields, separated by colons (:), with information such as the username, user ID (UID), group ID (GID), user description, home directory, and default shell.

• cut Command to Display Only Usernames:

  • To focus only on usernames, you can extract the first field of each line in /etc/passwd with the cut command:

    cut -d: -f1 /etc/passwd

  • This command lists only usernames, making it quick to scan the system for existing users.

• getent Command:

  • The getent command retrieves entries from system databases configured in /etc/nsswitch.conf, including the passwd database for users.

  • Run this command to list all users:

    getent passwd

  • The getent command is useful for querying network-based user databases as well if you’re in a corporate environment with directory services like LDAP.

2. Creating a New User in Ubuntu

• adduser Command:

  • The adduser command is the most user-friendly way to create new users. It prompts you to enter details like password, full name, room number, and more.

  • To create a user, use:

    sudo adduser <username>

  • Example:

    sudo adduser johndoe

  • Explanation of Steps:

    • This command will:

      • Create a new entry for johndoe in /etc/passwd and /etc/shadow.

      • Create a home directory at /home/johndoe.

      • Copy default configuration files from /etc/skel to the new home directory.

      • Set up user information and prompt for a password.

• useradd Command:

  • useradd is a low-level command for creating users, and it doesn’t prompt for additional information by default.

  • To create a user with useradd, use:

    sudo useradd <username>

  • Example:

    sudo useradd johndoe

  • After creating the user, set the password manually:

    sudo passwd johndoe

  • Difference Between useradd and adduser:

    • useradd only creates a user account, without creating a home directory or copying files from /etc/skel.

    • adduser is more comprehensive and typically recommended for new users.

3. Modifying Existing Users

• usermod Command:

  • The usermod command modifies user account settings, like username, home directory, or shell.

  • Common options:

    • Change Username:

      sudo usermod -l newname oldname

    • Change Home Directory:

      sudo usermod -d /new/home/directory -m username

    • Add User to a Group:

      sudo usermod -aG groupname username

    • Set Default Shell:

      sudo usermod -s /bin/bash username

  • Example:

    sudo usermod -aG sudo johndoe

  • This command adds johndoe to the sudo group, granting administrative privileges.

4. Deleting a User in Ubuntu

• deluser Command:

  • The deluser command is a simple way to remove a user account.

  • Basic syntax:

    sudo deluser <username>

  • Example:

    sudo deluser johndoe

  • This removes johndoe from /etc/passwd and /etc/shadow but retains the home directory by default.

  • Remove User and Home Directory:

    • To delete both the user and their home directory, use:

      sudo deluser --remove-home <username>

    • Example:

      sudo deluser --remove-home johndoe

    • This command deletes johndoe and removes /home/johndoe.

• userdel Command:

  • Similar to deluser, the userdel command deletes a user account.

  • Basic syntax:

    sudo userdel <username>

  • Example:

    sudo userdel johndoe

  • Remove Home Directory:

    • To remove the home directory as well, use:

      sudo userdel -r <username>

    • Example:

      sudo userdel -r johndoe

5. Additional Commands and Tips

• passwd Command:

  • The passwd command sets or changes a user’s password.

  • Basic syntax:

    sudo passwd <username>

  • Example:

    sudo passwd johndoe

  • It prompts you to enter a new password for the user and updates it in /etc/shadow.

• id Command:

  • The id command displays user identity information, including UID, GID, and groups.

  • Basic syntax:

    id <username>

  • Example:

    id johndoe

  • This command shows details like UID, primary GID, and supplementary groups.

• finger Command:

  • The finger command (if installed) provides detailed information about a user.

  • Install it with:

    sudo apt install finger

  • Example:

    finger johndoe

Summary

• Viewing Users: Use cat /etc/passwd, cut -d: -f1 /etc/passwd, or getent passwd.

• Creating Users: Use adduser for guided setup or useradd for a low-level approach.

• Modifying Users: Use usermod to update usernames, home directories, groups, or default shells.

• Deleting Users: Use deluser or userdel to remove user accounts, with options to delete home directories as well.

This guide should provide a solid foundation for managing users in Ubuntu. Let me know if you want more insights on any specific aspect!