What's the difference between `ifconfig`, `interfaces`, `ifup` and `ifdown`?

Question

I'm somewhat new to network interfaces and I'm confused with the difference between the 4 terms. I've seen the related question here: What is the difference between Network Manager and 'ifconfig' 'ifup', etc?, but this discusses the difference between all of the above and NetworkManager. I'm looking for something more specific between the 4 terms above.

I know that interfaces refers to the file at /etc/network/interfaces but all I see there is the lo interface. I would assume that I would see wlan0 and eth0 over there as well, as when I call ifconfig. I also know that the lo interfaces is activated by ifup -a at boot time.

Looking forward to your explanations.

Solution 1

In all the desktop editions of Ubuntu, networking is managed not by manual methods; that is, /etc/network/interfaces, but by Network Manager. Any interface, eth0 or wlan0 for example, that provides networking is, by default, managed by Network Manager.

The mostly deprecated commands ifup and ifdown control interfaces that are listed in /etc/network/interfaces. In the case you describe, the usual default configuration, only lo the loopback interface is listed and may be started and stopped with ifup/ifdown, although I consider this inadvisable. Usually, the system does this automatically so that no user intervention is required or expected.

In a server, with no graphical desktop, Network Manager isn't installed and so all interfaces are controlled in /etc/network/interfaces. In such cases, the configuration of the file, auto eth0, for example, means that the interface starts on boot. Again, typically no user intervention is required or expected. Here is a sample server configuration: How to connect to the internet

Solution 2

/etc/network/interfaces is a configuration file to be manually edited (the mention of loopback (or lo) is from the default file that the installer sets up). You won't see any other interfaces unless you added them there. If you haven't defined interfaces here but they're up and configured, then either some other service, such as Network Manager, Wicd, etc. is handling them, or you have manually configured them using the ifconfig or ip commands.

ifconfig, ifup and ifdown are all commands for manipulation of interfaces. The latter two have specific functions (as can be seen from their names). ifconfig (long since deprecated, but still commonly used) and ip can be used to configure devices (assign IPs, bring them up or down, etc.).

Comments

[eldosoa]

@the_Seppi, thanks but I'm looking for something unrelated to NetworkManager. I'm still confused as to where wlan0 and eth0 are configured since they're not in the /etc/network/interfaces file

[muru]

Network Manager doesn't need a GUI to run.

[chili555]

@muru Noted. Edited.