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Hey guys and welcome back. So now what I want to do is to change gears and talk about user

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notification. Now when we talk about user notification, what we're really talking about is just simply

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communicating to a particular user via some type of message. Now we have different types of messages

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that we can actually have on our system. One big distinction we're going to see is the concept of a

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pre-login message. This is a message you will see before you log into the system as well as a post

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login message which you can guess of course is a message after you log in to the system. Now really

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this might just seem like a surface level concept. We've got one that we see before and one that we

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see after we log in but this is actually something we should give a little bit of consideration to.

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Simply put, if you put too much information in a pre-login message, actually think about what is

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going on. You have a user who's not actually authenticated into the system. They've not even

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logged on yet after all and if you are displaying to them information which may be sensitive then

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ultimately you could be compromising the system or the security of your system. Similarly if you

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happen to be too guarded and you provide not enough information then maybe you are actually

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leaving out details that your users would really like to know about. Now there are some particular

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files that we can use to communicate this type of information. The very first file I want to talk

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to you about is the Etsy issue file. Try to remember this location. So let's say you try to log in to

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your particular server whatever it may be and you happen to be presented with a log on screen. You

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might happen to notice information such that it may tell you about the kernel for example or maybe

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it tells you about the system architecture. This information can actually be specified within the

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Etsy issue file because ultimately all this is is a text file that contains a message or say for

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example a system ID that is to be printed to the screen before the login prompt. Okay so this is

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something we see before login. Now one thing to consider here is that the Etsy issue file this

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is only going to be displayed for local logins. If you try to log in over the network maybe say over

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ssh you will not see any messages that you have specified within the Etsy issue file. Instead

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if you want to be able to see information when you log in remotely over say for example ssh

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instead you would want to make changes to a file called Etsy issue dot net and the name is kind of

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in the clue it's like the issue file but you're reaching it over the network. So if you happen

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to be using things like telnet or ssh these remote login technologies you can specify information to be

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printed onto the screen before the login prompt. Now when you happen to be constructing say for

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example the Etsy issue file there actually are some special values within this particular file

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and we'll actually get to see what those look like in the next nuggets but for now let me just

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highlight what some of these are. So when you log in through this particular file you will see some

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type of text information but you will also see some type of special characters and you'll be able to

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tell those special characters because they will be using backslashes so you may as well see a backslash

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b for example. Now when you happen to use the backslash b value within the Etsy issue file what

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this is actually going to do is going to display the speed of the connection this is actually going

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to display what is called the BOD rate. If you want to include this information you can just use

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this special character and the BOD rate i.e the speed of the connection will be displayed before

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the login prompt. Similarly if you happen to use the backslash d value this would actually display

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the current date this is kind of like what we talk about when we mention variables remember when we

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talked about bash scripting this is kind of like a variable right here this special character is going

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to represent whatever the current date happens to be if we want to see the actual operating system

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release number we could use the special character within the Etsy issue file backslash lowercase

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r and that would just print out to us the output of uname dash r which in this case here we can see

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this value. When we talk about the Etsy issue dot net file this is kind of a historical text

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file okay in that it's not automatically going to be read when we use an ssh session instead this

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was designed back in the days of telnet which is the unsecure and unencrypted version of ssh so to

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speak so if we happen to connect over ssh we absolutely can read in the values of Etsy issue

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dot net but like i say it's not going to be automatic we have to give some additional information

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and that information is that within the ssh ssh d underscore config file we actually have to point

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our banner setting to that particular location and we'll get to see what that looks like in the very

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next nugget but ultimately just understand by modifying this configuration file and changing

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this setting here to point to the Etsy issue dot net file we can indeed still receive the information

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from that configuration file over our ssh session. Now one thing i just feel i really have to kind

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of stress to you is that see all this really interesting and cool information that you can get

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using these special values such as backslash r to see the os release number and dash m to get the

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system architecture this can actually be a dangerous thing to do and again it's dangerous

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because what i just said before this is a pre-login banner we're seeing i.e this is going to be

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displayed to users who haven't actually even proven their own credentials so if you happen to be

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displaying information about your system say for example the type of architecture it has an outsider

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let's say for example a hacker could actually use this information for what is called information

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gathering reconnaissance and they could begin searching for particular vulnerabilities for

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that specific system you happen to be running so you really have to be careful advertising this

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type of information to absolutely anyone. Now another configuration file that we want to understand

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is the etse motd configuration file this is the message of the day file now this is a file that

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will be displayed post-login so once a user has logged in they can actually see the message of

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the day now you can actually be a little bit more relaxed about this information because of course

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the person who has logged in should have authenticated into the system therefore they should

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actually be an authorized user so now that we actually understand what these configuration files

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are how about we begin looking at them and making our own modifications to these files and also while

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we're at it look at a few additional commands that we can use to further communicate messages

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to our team well the good news is is that that is what we're going to be doing in the very next

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nugget so i hope this has been informative for you and i'd like to thank you for viewing