Hey guys and welcome back. So now what I want to do is to change gears and talk about user
notification. Now when we talk about user notification, what we're really talking about is just simply
communicating to a particular user via some type of message. Now we have different types of messages
that we can actually have on our system. One big distinction we're going to see is the concept of a
pre-login message. This is a message you will see before you log into the system as well as a post
login message which you can guess of course is a message after you log in to the system. Now really
this might just seem like a surface level concept. We've got one that we see before and one that we
see after we log in but this is actually something we should give a little bit of consideration to.
Simply put, if you put too much information in a pre-login message, actually think about what is
going on. You have a user who's not actually authenticated into the system. They've not even
logged on yet after all and if you are displaying to them information which may be sensitive then
ultimately you could be compromising the system or the security of your system. Similarly if you
happen to be too guarded and you provide not enough information then maybe you are actually
leaving out details that your users would really like to know about. Now there are some particular
files that we can use to communicate this type of information. The very first file I want to talk
to you about is the Etsy issue file. Try to remember this location. So let's say you try to log in to
your particular server whatever it may be and you happen to be presented with a log on screen. You
might happen to notice information such that it may tell you about the kernel for example or maybe
it tells you about the system architecture. This information can actually be specified within the
Etsy issue file because ultimately all this is is a text file that contains a message or say for
example a system ID that is to be printed to the screen before the login prompt. Okay so this is
something we see before login. Now one thing to consider here is that the Etsy issue file this
is only going to be displayed for local logins. If you try to log in over the network maybe say over
ssh you will not see any messages that you have specified within the Etsy issue file. Instead
if you want to be able to see information when you log in remotely over say for example ssh
instead you would want to make changes to a file called Etsy issue dot net and the name is kind of
in the clue it's like the issue file but you're reaching it over the network. So if you happen
to be using things like telnet or ssh these remote login technologies you can specify information to be
printed onto the screen before the login prompt. Now when you happen to be constructing say for
example the Etsy issue file there actually are some special values within this particular file
and we'll actually get to see what those look like in the next nuggets but for now let me just
highlight what some of these are. So when you log in through this particular file you will see some
type of text information but you will also see some type of special characters and you'll be able to
tell those special characters because they will be using backslashes so you may as well see a backslash
b for example. Now when you happen to use the backslash b value within the Etsy issue file what
this is actually going to do is going to display the speed of the connection this is actually going
to display what is called the BOD rate. If you want to include this information you can just use
this special character and the BOD rate i.e the speed of the connection will be displayed before
the login prompt. Similarly if you happen to use the backslash d value this would actually display
the current date this is kind of like what we talk about when we mention variables remember when we
talked about bash scripting this is kind of like a variable right here this special character is going
to represent whatever the current date happens to be if we want to see the actual operating system
release number we could use the special character within the Etsy issue file backslash lowercase
r and that would just print out to us the output of uname dash r which in this case here we can see
this value. When we talk about the Etsy issue dot net file this is kind of a historical text
file okay in that it's not automatically going to be read when we use an ssh session instead this
was designed back in the days of telnet which is the unsecure and unencrypted version of ssh so to
speak so if we happen to connect over ssh we absolutely can read in the values of Etsy issue
dot net but like i say it's not going to be automatic we have to give some additional information
and that information is that within the ssh ssh d underscore config file we actually have to point
our banner setting to that particular location and we'll get to see what that looks like in the very
next nugget but ultimately just understand by modifying this configuration file and changing
this setting here to point to the Etsy issue dot net file we can indeed still receive the information
from that configuration file over our ssh session. Now one thing i just feel i really have to kind
of stress to you is that see all this really interesting and cool information that you can get
using these special values such as backslash r to see the os release number and dash m to get the
system architecture this can actually be a dangerous thing to do and again it's dangerous
because what i just said before this is a pre-login banner we're seeing i.e this is going to be
displayed to users who haven't actually even proven their own credentials so if you happen to be
displaying information about your system say for example the type of architecture it has an outsider
let's say for example a hacker could actually use this information for what is called information
gathering reconnaissance and they could begin searching for particular vulnerabilities for
that specific system you happen to be running so you really have to be careful advertising this
type of information to absolutely anyone. Now another configuration file that we want to understand
is the etse motd configuration file this is the message of the day file now this is a file that
will be displayed post-login so once a user has logged in they can actually see the message of
the day now you can actually be a little bit more relaxed about this information because of course
the person who has logged in should have authenticated into the system therefore they should
actually be an authorized user so now that we actually understand what these configuration files
are how about we begin looking at them and making our own modifications to these files and also while
we're at it look at a few additional commands that we can use to further communicate messages
to our team well the good news is is that that is what we're going to be doing in the very next
nugget so i hope this has been informative for you and i'd like to thank you for viewing