After starting Linux, log in as root. The first task is to check to check the network interface card.
First, you can use dmesg to display the kernel ring buffer. Instead of executing the command alone, use dmesg | less instead. This feeds the content to a pager so that you can view it page-by-page and search for specific words. A search is started by pressing the slash (/) key.
If you are more certain than not that a NIC is recognized, search for eth for an Ethernet interface. Note that a computer may have multiple NICs, so you may find eth0, eth1 and etc. If you are looking for a wireless device, it is usually listed as wlan0, wlan1 and so on. Note that these interface naming conventions are somewhat distribution dependent, and the mentioned interface names are used in Debian distributions.
If you find the eth0 or eth1 entries, then you can proceed to the next section.
However, if you cannot these entries, that means the NIC may not be supported, or its driver is missing. For certain NICs, the firmware needs to supplied by the host computer, and if the firmware is missing the NIC cannot be used. In all of these cases, it is important to check the hardware.
If your NIC is a PCI device (this includes PCIe and chip-set devices), you can use lspci to locate it. lspci can take a few options, it may be helpful to run it as lspci -k so that kernel modules (drivers) are also listed.
The output of lspci can be long and confusing. Again, use lspci -k | less so that you can display the content page-by-page. Look for Ethernet if you are looking for a Ethernet NIC. Once you locate it, see if it has a driver. You can confirm this by reading the line starting with Kernel driver in use: .....
If your NIC is a USB device, you can use lsusb to locate it. lsusb -t | less is a useful command, as it displays the drivers (if loaded) and tree structure of USB hubs and devices.
If you can locate a NIC using lspci or lsusb, but it does not have a loaded driver, you should look for its driver. It is possible that your Linux distribution may not have the driver or firmware installed due to open source requirements. Some vendors do not license their drivers as open source code, making it inappropriate for certain distributions to install them by default.