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Network files and commands. There are

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many network files and commands that

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needs to be used in order to configure

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your machine and bring it online or

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bring it to the network, so it could

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communicate from one machine to another.

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It should have an interface, an interface detection.

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[No audio]

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Assigning an IP address to the system is

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very important when you bring up a

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system and you need to have it on the

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network. The interface configuration

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files are the first one is /etc/nsswitch.conf file

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This file is located in

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every Linux distribution. In fact, all

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these files that I'm going to talk about

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all of them are and will be in your

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Linux system. So the first one is nsswitch.conf,

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which tells the

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system where is where it should resolve

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its hostname to IP address. So let's

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look at our Linux machine and then we

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will find out how to read these files.

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[No audio]

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Let's clear the screen.

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Okay, the first file that we're going to look at

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it's /etc/nsswitch. So just do cat

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on /etc/nsswitch.conf file.

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You will see it starting with host let's

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let's do more on it instead of just cat.

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So this will read the file page by

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page. Okay, so all these stuff, anything

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that starts with pound, it means it's

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just a comment. Anything that you want

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to have it in effect, just remove the

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comment. So let's go through it. Let's

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go to the point where you don't see the

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comment. So here it's starting from this

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page on it says a passwd file. So the

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first thing is telling you to look for

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the passwd file in the files. Don't go

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anywhere, there is no active directory,

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there is no other NIS service that's

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running that's going to give you the

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passwd, so it look for /etc/passwd.

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Shadow is also /etc/shadow, that's local,

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group is also /etc/group. And when you

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come down to host right here, it's going

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to tell you the the host information of

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your system is located in the files. And

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that is /etc/host. And then it's gonna

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say if you can't find it, then go to DNS.

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DNS is an other service that is

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installed on a Linux machine or it can

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be installed in Windows machine. We'll

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cover that later on. But for now, this

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is what the nsswitch file looks like, and if

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you want your host to be resolved with

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DNS first, you switch DNS here to here

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and file comes the second. So this is

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the nsswitch file. You're going to be

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seeing this configuration of this file

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many times while you're doing system

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administration. Next one we're going to

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look at is /etc/hosts. /etc/hosts file is

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where you define your system IP address

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and system hostname. So if my system IP

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address is ifconfig, it's 192.168.1.14,

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I could go into that /etc/file but

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by becoming root.

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[No audio]

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vi the file, and I

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could go at the bottom and I could put

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192.168.1.14. And the host

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name of my machine is, forgot, let me save

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it, and there you go, MyFirstLinuxOS. So

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let's do it again.

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My, it doesn't matter

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uppercase, lowercase myfirstlinuxos.

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myfirstlinuxos. So now if you ping myfirstlinuxos,

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it's going to ping your

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IP address. You see right here, the one

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that you specified in the /etc/ file. So

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that's what /etc/ file does. It's a

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small, very tiny version of DNS that's

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sitting in your machine. The next one we

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have /etc/sysconfig/network file. This file,

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[Author typing]

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sorry, this it's network I believe.

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No, network, probably, yup I'm right. So this

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is the file where you specify your host

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name as well. Right now it's empty

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because we have hardcoded the hostname,

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but if you want to change it, you could

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modify it here and a certain other

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parameters can be set to, of course, you

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are more than welcome to look it up more

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on the network file.

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The next file that we're going to be

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covering is actually the file, that's

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where you specify your IP address on all

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the network, all the subnet mask, and

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gateway. And when you are in the

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directory, /etc/sysconfig/network-scripts,

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I want you to do ls -ltr,

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and the last file you're going to see

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is ifcfg-enp0s3. And

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what is, this last one, it's actually

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your interface. If you go if config, and

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you will see right here, this is the

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name of your interface. So remember,

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every time all those interfaces files

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always start with ifcfg-, and the

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interface name. So when you vi that

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file, here you will see the BOOTPROTO

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is defined as dhcp. You could change

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that at here as static and then you

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could define the IP address, you could

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define subnet mask, gateway, and this way

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your IP address becomes prominent in

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your machine and does not change. So

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these are a few few of the files that I

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really want you to understand and

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memorize it because if you are going to

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go into Linux jobs and you're going to

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be applying for it. Oftentimes, you're

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going to get questions on these where

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these files are, what the files do,

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where they're located, and so on. So

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let's exit out of this file. The last

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file I have is /etc/resolve.conf.

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/etc/resolve.conf specifies your

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DNS server. DNS server is again once

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again, it actually resolve hostname to IP,

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IP to hostname, and hostname to hostname.

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So if you define it here, every time you

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go to www.google.com and hit enter, it

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knows Google is, I have to go into this

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as my gateway, I have to go to my

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gateway, which is right now acting as a

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DNS server, I'm going to go to my DNS

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server and ask where is Google and how

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to translate Google to IP address. And it

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has translated, and this is the IP

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address of Google. Let's go back to our

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lesson. The next one, we have the

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network commands. The network commands,

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we have learned ping already. If you

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wanted to ping a server, let's say ping

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the www.hotmail.com, that's the server

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outside that command that you will run

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is ping. ifconfig tells you what your

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interfaces are in the system. We have

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right now three interfaces, the local

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one does not count as an interface. And

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other one, you can ignore it, the only

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one that I have is just one and it's

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this right there. And it's telling me my

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IP is configured this. Then you have ifup or

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ifdown. If you want to bring down

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this interface, if you don't want to

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network, you could type ifup sorry, ifdown,

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or if you want to bring it back up

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your type ifup. Then the next one, we

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have netstat. netstat, you can run with

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different options, I run usually with rnv.

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This one tells you your gateway, how

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your traffic is flowing from which

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interfaces it's going from. And the last

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one we're going to cover is tcpdump.

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tcpdump is actually traces every single

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transactions that are leaving your

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machine and coming into your machine.

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The command to run is simply tcpdump.

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You have to specify i with the

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interface, which interface you are

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sniffing. It's basically a sniffing

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tool. And then you run it and you will

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see every listening coming in

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going out, it's actually listed here. So

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that's how you actually run this TCP

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command, that's how you run all these

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commands and please memorize it. Please

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run a man command on each and every one

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of them and familiarize yourself how

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these network commands and files work.

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