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Troubleshooting

IP Configuration​

Use ifconfig or ip to see if the interface is up, and if so, if it is configured.

Network Driver​

If the interface can't be brought up, maybe the correct device driver for the network card(s) is not loaded. Check with lsmod if the network driver is loaded as a kernel module, or by examining relevant pseudo-files in /proc and /sys, such as /proc/interrupts or /sys/class/net.

Connectivity​

Use ping to see if the network is visible, checking for response time and packet loss. traceroute can follow packets through the network, while mtr can do this in a continuous fashion. Use of these utilities can tell you if the problem is local or on the Internet.

Default Gateway and Routing Configuration​

Run route -n and see if the routing table makes sense.

Hostname Resolution​

Run dig or host on a URL and see if DNS is working properly.