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[No audio]

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Talking to users.

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The users are the ones that are logged into

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your system and some of them have their applications

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running, some of them have databases running.

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Those are the users that log into the Linux system and there

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are often times you do need to talk to them.

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When I say talk to them, not like face to

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face but you do need to communicate to them that

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if you need to bring down your Linux system or

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if there's a maintenance or if there are any commands

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or any application that they are running, that are causing stress

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on the system, you do need to identify them. Command

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to find out is just typing users.

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Then there is a command called wall.

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wall is the command that is broadcast your message

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to everyone who is logged into the Linux system.

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And then there is last command which is write

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command is dedicated to a user, one specific user.

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It does not go out or your

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message does not broadcast it to everyone.

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It's just one user to another.

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So we'll log into our Linux system and we will

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try all these commands one by one and we will

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see how we could talk to other users.

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I have my Linux machine up and running

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and I am logged in as myself.

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And I could also see here I'm logged in as myself.

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The first command that I have is wall.

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So before I go into this first command, sorry first command is user,

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let's find out who is logged into the system.

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But what I was going to say is

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before we run this command I will log

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into another terminal as a different user.

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So to log into through another terminal, which

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would be the PuTTY terminal, I would need

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the IP address of this Linux machine.

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Let's check the IP address.

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You guys know that, right? Yes.

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We could run ifconfig, and the reason I

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put it more, I'm sure you know that

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so I could see the output one page at a time.

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I see my IP right here is

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192.168.1.12.

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I will take that IP and I

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will put it into my PuTTY session.

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192.168.1.12.

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[No audio]

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You hit enter.

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It will prompt you for the server SSH

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key that you wanted to save it.

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You could just say click Yes.

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And now this time I want you

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to log in as a different user.

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The user that I created earlier, I called the

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spider and put in the password for the spider.

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Now I'm logged in as a spider.

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If you logged in as yourself on your terminal,

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you can log out, or you open up another

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PuTTY terminal and log into a different user.

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And those users are the ones that we created earlier.

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You could pick any user, it doesn't really matter.

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Now we will see how many

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users are logged into our system.

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The command to see is just type, sorry, users.

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And you'll see there are three users logged in.

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Two of them are the ones

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sessions that are used by myself.

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And the third one is the spider.

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spider is the one is this one that I just logged into.

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Now I'm here, right now, in this

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session, I am logged in as myself.

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In this session, I'm logged in as spider.

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So if I want to reboot this machine or I

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want to shut it down for some kind of maintenance,

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then I have to let everyone know who is logged

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into my machine, that I am shutting down this machine.

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So please save your work

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if you are editing a file or whatever that you're

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doing, log off the system so I could reboot it.

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And how do I broadcast that?

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I will just type the command wall.

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I'll hit Enter.

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Enter one more time if you want to put a space,

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and then you could type whatever the

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message that you want to type here.

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I'll type, Please logoff,

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This system is coming down for maintenance.

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[No audio]

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Imran. That's my message.

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And once you have that, then you type Control d.

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As soon as you type Control d, you see on the

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left hand side, the message came up right away.

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Please log off,

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The system is coming down for maintenance.

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So this message is not only

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directed towards spider, the user spider.

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It is directed to anyone who is logged in.

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It will go to everyone's terminal

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and you see that message.

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And now you notice you don't have a prompt.

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You're just inside of your message,

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you simply hit Enter,

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you'll get your prompt back.

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Now what if I want to write

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a message to a specific user?

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So in this case, who are the users?

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Right now I see that two sessions being used by

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iafzal, and one session is used by spider.

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I want to send a message to spider saying,

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hey spider, you are using some of the resources

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through this script or through your application.

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Can you please stop the application because

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it's causing stress on the system.

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These are the type of messages you have to

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send it to the user when you become a

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system administrator or you have a root privileges.

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So to write to user, you just

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simply type write and the username spider.

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Then you hit Enter.

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As soon as you hit Enter, you will

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see on the left hand side, the spider

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is getting the message right away from you.

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I'll put, Hi Spider,

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[No audio]

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your web is getting bigger.

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Please stop spreading your web.

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It's just an example of funny sentence.

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So I have written this.

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I'll hit Enter.

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As soon as I hit Enter, you'll see on the

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left hand side Hi Spider,, your web is getting bigger.

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Please stop spreading your web.

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This message is not directed toward

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everyone who is logged in.

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It's only going to the user spider.

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And if you see right here,

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it's saying Message from iafzal.

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It means it's coming from this user, from this machine. Perfect.

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[No audio]

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Type write iafzal, and right here I

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say, ok Imran I will try my best.

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Thanks Spider.

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[No audio]

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And then control G.

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That's it, that's how you communicate with each users.

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And I have communicated through iafzal, of course.

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And most of the time that communication

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takes place through the user se mes

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Root is the one who sends those messages

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because root has the highest level of permissions,

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higher level to reboot the system, to bring

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it down, to perform the maintenance.

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That's why we run these commands.

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So again, users, wall, write.

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You can log into three

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different sessions, try these commands.

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It's going to be fun writing back and forth.

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And if you're already in an environment, you're working with

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a corporate, you could type the write messages to other

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users just to try out, just for fun.

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[No audio]