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- So we have just seen how some
packages have dependencies,

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and these dependencies
often relate to libraries.

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Now the thing in libraries

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is that common functionality
is often provided by a library.

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And the nice thing about a library

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is that different software packages

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can use the same libraries.

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And that is how libraries make
working with software easier.

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They provide common functionality

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that can be used by multiple packages,

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even if some of the
libraries are very specific.

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But some other libraries are more generic.

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One of the most generic
libraries is glibc,

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also known as libc.

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That's the C-library that provides

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all of the common functions
in the Linux operating system.

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And when installing software packages,

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libraries normally are
installed as dependencies,

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if they are not already present of course.

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Let me show you how
these libraries are used.

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So I would like to show you
a little bit about libraries.

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And libraries, in order to explore them,

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you need a full path
name to an application.

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And ldd is the program that I want to use.

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So I'm using ldd on something
we have not seen before,

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${which passwd}.

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What is that?

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Well normally,

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ldd wants a path name.

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But here I'm using a solution

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that is creating the
path name dynamically.

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The ${} are implementing what
we call command substitution.

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So the command, which passwd,

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is executed, it generates its result,

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and ldd works on the
result of the command,

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which is a very nice and
frequently used method

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to provide content in a dynamic way.

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And there we can see all
these different libraries.

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Now most of these libraries
may not need too much,

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but I wanna pick out a couple of them,

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like libc.

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Libc is the generic C-library.

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The C-library contains the main functions

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of the Linux operating system.

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We have libpam,

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which is about pluggable
authentication models.

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We have libcrypt,

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which is providing cryptography.

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You can imagine that in passwords,

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in password management,

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different solutions for
cryptography may be implemented.

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And instead of putting that
in the individual module,

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a generic library is used, libcrypt.

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And this libcrypt library can be used

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by many other software packages

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that need this cryptography functionality.

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And that is how libraries

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make working with Linux
really much easier.

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Most of the libraries that are needed

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by the software packages
are dynamically loaded.

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And you can use ldd, as you see here,

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to get an overview of libraries

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that are loaded by
specific software packets.

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And that is providing
insight in functionality

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that is provided by the software package.

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And that can be very useful.