Week 2: User and Software Management

Part 1: User Management

There’re two types of user accounts: superuser or root user and standard users. The root user is a special user account used for system administration and has all the rights or permissions to make modifications in all modes.

It’s advised that you avoid logging into the system as a root user for security reasons and to avoid serious damages caused by mistakes in entering commands. If a task requires root level permissions, then you can use the sudo command to run it as a root user. The sudo command requires the user who issued it to know the root password.

1.1 Creating a Sudo User

Not every standard user can issue the sudo command. To give a standard user a sudo access, we need to add the user to the /etc/sudoers file. This can be done indirectly by adding the user to the wheel group. This can be done by logging as a root user, and using the command usermod -aG wheel <username>.

# login as a root
sudo su -
usermod -aG wheel khalid

You can test that the user has superuser privileges by logging in again and prepending sudo to a command that requires superuser privileges. For example, listing the contents of the /root directory.

# login again using su - <username> or by logging out using exit
localhost login: khalid
$ sudo ls /root

1.2 Creating a new group

The command groupadd <group-name> is used to create a new user group.

$ groupadd staff

1.3 Listing groups

To list all the groups that a user belongs to, use the command groups <username>:

$ groups khalid
khalid wheel

To find all the group names on the system, you can list the /etc/group file which contains one line for each group.

$ cat /etc/group
khalid:x:1000:khalid
wheel:x:10:khalid
....
..
sshd:x:74:
ali:x:10001:

1.4 Adding an existing user to a group

$ usermod -aG staff khalid

1.5 Listing all users on the system

The /etc/passwd file contains one line for each user account. Each line contains fields separated by a colon (:) symbol. The first field is the username.

$ cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
...
..
...
khalid:x:1000:1000:khalid:/home/khalid:/bin/bash

1.6 Adding a new user

To add a user to the system, issue the command useradd <username>. This command should be issued as a root user or using sudo. Otherwise, you will get a Permission denied error. After the user is created, you can use the passwd <username> command to set the user passwd.

Alternatively, you can use the adduser command to add a new user to interactively add a user to the system.

Both useradd and adduser commands create new users on a Linux system.

$ sudo useradd ali

1.7 Changing the password

To change the password of an existing user, use the command passwd:

$ sudo passwd ali

Part 2: Software Management

Installing and uninstalling software in Linux can be done in various ways. The simplest way is to use a package manager. A package manager is a tool for installing, updating and removing software packages. Ubuntu uses the apt package manager.

It’s important to note that installing software often requires a root user privilege, so you need to prepend the apt command with sudo.

2.1 Installing a new software

To install a new package, use apt install <package_name>. For example to install the Apache web server, use the command:

$ sudo apt install apache2

2.2 Updating installed packages or software

To download and install all packages, type the command:

$ sudo apt update

To update a specific package or software, use sudo apt install --only-upgrade <package_name>. Example:

$ sudo apt --only-upgrade install apache2

If you would like to patch your system and restrict the update to only security-related package updates, use the unattended-upgrade package:

$ sudo apt install unattended-upgrades
$ sudo unattended-upgrade -d --dry-run

2.3 Removing/Uninstalling a new software

To remove an existing package, use sudo apt purge <package_name>. For example to uninstall [the GNU nano text editor], use the command:

$ sudo apt purge nano

Issues

Q1: How to check if I’m connecting to the Internet?

Try the ping utility: ping 1.1.1.1 and use the command ip address to see if you have an ip address.

Q2: Why is my system not connecting to the Internet?

Edit the file /etc/sysconfig/network-scripts/ifcfg-<interface_name> (replace interface_name with the name of your network interface; e.g., enp0s3) and change the line that has ONBOOT=no to ONBOOT=yes. You need to restart the Operating System to see the effect.