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- Okay. In the previous video

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you have learned how to
use man, man is awesome.

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As long as you know which command to use

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but what are you going to do

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if you don't know which command to use?

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Well, then you are
going to use the man DB.

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The thing is that an index

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of man pages is created in
the man DB, the man database.

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And you can use man minus K

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or apropos to search
the man DB on keywords.

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In some cases you will
get nothing appropriate.

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If that happens.

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If you are looking for
something, not very common

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then it may happen that
there's just nothing matching

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or you are looking for.

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But it may also mean that
your man DB is not updated.

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And if that is the case,
well, you need to update it.

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Sudo, man, DB is what
you are going to use.

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Let me demonstrate.

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(keyboard typing)

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All right.

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I am typing man

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minus K man, minus K or
apropos it's the same.

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So you decide what you want to use.

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I'm using man minus K user and oh no

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I am getting nothing appropriate.

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That is definitely not good.

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But it's something that may happen

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on newly installed systems.

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So how come isn't this taken care

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of when installing the
system? Well actually no.

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The thing is that the man DB is generated

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by a scheduled job, a Cron
job, as you call it in Linux.

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And this Cron job runs
every, every day, once a day.

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And this system was installed
not so very long ago.

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So this is a brand new system

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and that means that the Cron job has

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just not been started yet.

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And you know what

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I'm going to show you? man

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so that we can actually
practice using man and

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and find out how to use man minus K.

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So man, man, and I'm going to search

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for minus K so slash minus K.

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Look at the lower left corner

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slash minus K is bringing me

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to the first and the second occurrence.

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That's not what I need.

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So I'm pressing N to get to
the next and N again and there

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We can see equivalent

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to apropos search the
short manual descriptions

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see apropos for details.

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So we are in the wrong
spot and I need to use man

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on apropos to get the
appropriate information.

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And there we get an explanation

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and we can see the database searched

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by apropos is updated
by the man DB program.

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So man DB program, and it's
also telling us this may be run

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by a periodic Cron job.

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That's exactly what was happening

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but how do we deal with this man DB?

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Well, man, should know,
man, man DB, there we go.

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And man DB always do a quick check.

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If you're in the right section

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if you see a one or an
eight, then you are good.

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If you see a three or something
else that is not a one

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or an eight, then are probably
in the wrong location.

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So what do we see?

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We see that man DB
comes from section eight

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section eight means that
it's an admin command.

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And that means

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(keyboard typing)

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that if I want to
regenerate the man DB just

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typing man DB is not going to work.

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As you can see, I'm getting
warning cannot create

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and more warning cannot
create, cannot create.

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That means that we have
a permission issue.

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So I'm going to repeat this command.

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I look at my command line.

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I have my cursor blinking
at the end of the line.

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I'm using control A

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control a brings your cursor
to the start of the line

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and control E to the end of the line.

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But I need to be at the start

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of the line because I want
to type sudo in front of it.

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And of course you can remove
this command and try again

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but it's so much more convenient.

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If you can just move your cursor

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to the start of the line, I'm using sudo.

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And in order to do sudo,
I need my password.

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There we go.

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And now it is updating the man DB.

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Even if it's doing the right thing

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you do see a couple of field messages.

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Please ignore the field messages.

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What you should be looking

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for is the third line from the bottom.

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Almost 8,000 manual pages
were edited and the result is

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that right now I can use man minus K user.

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And oh boy, did you see that?

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This is what I call too much output.

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Sometimes on Linux,
you get too much output

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and I will tell you in much more detail

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what we are going to do later

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but now I'm going to give
you a quick look ahead.

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If you get so much output,
use a pipe, the pipe

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will take the result of the
first command and use it

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as input for the second command.

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And you have two options,
man, minus K user pipe, less

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which will, which will
send it to the less pager.

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And in this pager, you can
watch the results screen

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by screen, use a space
bar to move forward.

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But Hey, this is still too much reading.

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Maybe you wanna do something smarter.

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If we repeat the output of man minus K,

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Then you can see that in the first column

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there is the section
behind all of the commands

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and we are going to use
this section number to

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find the command that we need.

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Now, what is the thing?

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If I'm looking for users
and probably I'm looking

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for something like I wanna create a user

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and what do you think,
can you create a user

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without using sudo? Of
course not creating user

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requires root privileges.

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And that means that the
command that I'm looking

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for most likely is
documented in section eight.

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(typing)

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So I'm going to pipe this time, the output

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of man minus K user to the grep command.

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He grep command is also
one of these commands

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that we will explore in
much more detail later.

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But for now you should know
that the grep command is one of

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The most useful commands in Linux.

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It's a filtering utility and

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by piping the output to
grep eight man minus K

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user is only going to show these
lines that contain an eight

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and there near the bottom

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you can see user add and
user del and user mod.

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And in case you are
wondering why doesn't man

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minus K have an option
to work with specific

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specific sections of man.

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Well, that is because

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of something that we call
the Linux philosophy.

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In the Linux philosophy

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It's very common not to
program all the functionality

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in one command

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because that would make
one big bloated command.

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You wanna make sure that you
pipe the output of one command

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to another command, which
is a smart combination

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of commands to get you exactly
the result that you wanna do.

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So this is why we are using pipes a lot

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in Linux to combine functionality.

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And by the time you are
done with this course

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you will know how to do it

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Exactly.