How to check what is my network card on Ubuntu?

If you want to give the best output, something like this would be best appreciated.

$ lspci | awk '/[Nn]et/ {print $1}' | xargs -i% lspci -ks %
09:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168 PCI Express Gigabit Ethernet controller (rev 03)
    Subsystem: Gigabyte Technology Co., Ltd Motherboard
    Kernel driver in use: r8169
0a:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168 PCI Express Gigabit Ethernet controller (rev 03)
    Subsystem: Gigabyte Technology Co., Ltd Motherboard
    Kernel driver in use: r8169

Or sudo lshw -c network but you might want to exclude some of the information (ip/serials/etc) but it might not bother you though.

Run this on a terminal (Ctrl+Alt+T):

lspci | grep -i net

Maybe your interface card has changed from eth0 to eth1. This has happened often with me. To check, type this command:

sudo ls /sys/class/net