I have an old desktop computer with CentOS 7 operating system installed without GUI. I wanted to connect to internet using a USB wifi adapter. My internet router was located in a different room and LAN cable was not available with me. So I used netgear USB wifi adapter for establishing the internet connection. This post is about troubleshooting and fixing the connectivity issue.
The model that I have used is Netgear WNA3100M Wireless-N300 USB Mini Adapter. The picture is shown below.

I checked the network interfaces and ip address using ifconfig command. It listed an interface named wlp18s0b1. But no ip address was assigned.
I tried ifup command. But it gave me an error as follows.
ifup wlp18s0b1 /sbin/ifup: configuration for wlp18s0b1 not found. Usage: ifup
Then I tried listing the USB interfaces using lsusb command and it listed the network adapter usb device. This means that the device is getting detected.
The next steps that I tried are using the nmcli command.
The following command will list all the available Wifi connection profiles.
nmcli connection show
To connect to a wifi network, use the below command. You have to pass your wifi ssid and password as shown below as arguments.
nmcli dev wifi connect your-wifi-ssid password wifi-password
My desktop got connected to the internet after triggering the above command. After this, every time I start my computer, if the desktop is not automatically connected to the internet, I issue the following commands.
nmcli connection show nmcli connection up your-wifi-connection
This solution helped me. Hope this will help someone else also :).