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In this video, we'll zoom
into dependencies a little bit.

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So what are dependencies? Well, dependencies are
often libraries that provide common functionality to applications.

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Other dependencies might
exist as well.

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Think about running a Python script. In order to
run a Python script, Python needs to be installed.

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Dependencies are always provided in independently managed
packages, and that can make it quite

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complex. But fortunately, the package managers
like DNF and APT provide a solution.

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Now, about these libraries. Libraries are very
commonly used in Linux to make working with

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software easier because they provide common functionality
that may be used by multiple packages.

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If you want to analyze network packages, for instance,
there is the packet capture library libpcap. There's also libc,

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which is a more common library. This is the
C library that provides all the common functions in the

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Linux operating system and you will see it as
a dependency for all packages that you are using.

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When you are installing software packages, libraries
are installed as dependencies and the LDD

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command can can be used to find
out about libraries that are currently installed.

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Now, while working with libraries, there
is the issue of library versions.

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You can only have one version
of a library on a system.

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So how are you going to do
that if you want to run applications that

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require different versions on the same system?
Well, then you need to isolate the application.

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And there are two ways that you can
use isolation. Either you are going to run

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your application as a container, which we'll talk
about about in lesson 19, or you are

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going to use an isolated application using
Snap on Ubuntu or Flatpak on other distributions.

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Let's have a quick look at these libraries
before talking a bit more about package managers.

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So I am going to use sudo ldd LDD is
d command if you want to find out about libraries.

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And I'm going to do that on the result
of the command, which passwd Remember, if you put

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a command like this between dollar and parentheses,
you will work with the result of the command.

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And what do we see? Well, we see
all the libraries, including the C library libc

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so 6, but also other libraries that
define how this command is doing its work.

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Like libpam, which is for pluggable authentication modules.
That's a framework that is using authentication like

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lib audit, which means that you can audit
messages that are generated by this utility in

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lib SELinux, because this is a red hat
system where Selinux is used for more security.

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Now the issue about these libraries is
that they all need to be installed when

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you install your packages. And in the
next video you'll find out how that works.