ifconfig stands for "interface configuration." 

It is used to *view and change the configuration* of the network interfaces on your system.

Running the ifconfig command with no arguments, like this:


[source,bash]
----
ifconfig
----

...displays information about all network interfaces currently in operation. The output will resemble the following:


[source,bash]
----

eth0      Link encap:Ethernet  *HWaddr* 09:00:12:90:e3:e5 // <1>
          inet addr:192.168.1.29 Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:fe70:e3f5/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:54071 errors:1 dropped:0 overruns:0 frame:0
          TX packets:48515 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:22009423 (20.9 MiB)  TX bytes:25690847 (24.5 MiB)
          Interrupt:10 Base address:0xd020 
lo        Link encap:Local Loopback   // <2>
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:83 errors:0 dropped:0 overruns:0 frame:0
          TX packets:83 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:7766 (7.5 KiB)  TX bytes:7766 (7.5 KiB)
----
<1> *HWaddr* This is your MAC address
<1> *eth0* is the first Ethernet interface. (Additional Ethernet interfaces would be named *eth1,* *eth2,* etc.) This type of interface is usually a NIC connected to the network by a category 5 cable.
<2> *lo* is the loopback interface. This is a special network interface that the system uses to communicate with itself.



*Configuring an interface*

ifconfig can be used at the command line to configure (or re-configure) a network interface. 

This is often unnecessary since this configuration is often handled by a script when you boot the system. If you'd like to do so manually, you will need superuser privileges, so we'll use sudo again when running these commands.