Welcome to the lesson on Software Management. In the last two decades, managing software on Linux operating systems has become very convenient, thanks to the package management systems. In the past, one had to download the source code, compile, and place the binaries and libraries in their respective locations, and in the process also handle any conflicts with existing libraries, etc. But today, this has been made very convenient because the package management system would take care of all those details for you. Why do we need to have a package manager? It is very simple. We need tools to install, update, remove, and manage the software, and doing it manually would be quite painful, particularly with the number of packages running into several thousands, which is typical for a fully installed Linux operating system today. We also want to be able to install the new and updated software across the network. That is, we may not have the software available as a disk or as a USB drive with us readily, and we

may want to do the updating over the Internet. 
Sometimes we are interested in knowing what are the various files that are supplied by a given package. And sometimes we are also wondering, which package has supplied a particular executable that we have become familiar using it. So, both ways a package manager would let you look up the database and answer your queries. So, the database of packages on the Linux operating system would include the versions, and their compatibility and requirements, so that it makes your life quite easy in upgrading or adding new packages without disturbing the existing setup. 
And how do you verify whether the software tools that you are installing are coming from the original software vendor or the authentic Linux source? There are ways by which signatures are placed along with the software tools, which help you verify the authenticity of the source of these tools, so it is a very good idea to pick up software tools for any Linux operating system from the respective source of that

particular flavor of Linux, and not as a binary 
from any arbitrary website on the Internet. 
There are some packages which come as a 
source code, and you need tools to build executable versions of those tools, and package 
manager also would take care of such aspects. This is particularly true of kernel modules, 
so that whenever the kernel gets updated, certain modules need to be compiled for that 
particular version and made available. 
There are two major package types that are 
available. One is RPM and the other is DEB or Debian. The RPM format is followed originally from 
the Red Hat Linux operating system. Derived from the Red Hat operating system our CentOS, Fedora 
and Oracle Linux. The RPM format is also followed by the SUSE Enterprise Linux firmware the 
OpenSUSE operating system has been derived. 
The Debian format of package type is 
from the Debian Linux operating system from where the Ubuntu Linux has been derived.

The Mint Linux is also a derivative of Ubuntu, 
and therefore it is also a Debian type of Linux. Topics is another flavor, which is used 
to run Linux off a media drive, such as a CD drive or a DVD drive, and that 
is also a derivative from Debian. 
As you have noticed, Ubuntu is the most 
popular desktop operating system, including its derivatives, and therefore the package type 
that we must be familiar with is Debian package. Whereas those who are maintaining Linux servers, they should be familiarized 
with the RPM package type. 
Let us check what type of an operating system 
we have on the desktop that we are using. I would just open the shell to check what is 
that. Let us see what type of an operating system 
we have. So, we can run the command lsb release 
with an option minus a, and you see that the 
desktop operating system that is right now 
running on my machine is Ubuntu version 20.04 LTS.

and the nickname for this operating 
system with the version 20.04 is focal. So, when you look for some packages 
for this particular version of Ubuntu, you could actually search by the nickname which 
makes it a little easier to identify those. 
Linux operating system is available 
for a wide variety of architectures. So, in the past, we had the 32-bit hardware, so 
we would have Linux for i386 architecture or x86 architecture. Today we have 64-bit hardware, and 
therefore, we would actually have the operating system for AMD 64 or x86 underscore 64, as the 
architecture. And Linux is now also available on arm architecture which is popularly used by 
the mobile phones. Linux is also available for power PC architecture.
You may have heard of the RISC fifth generation risk five architecture. For 
example, in the context of Shakti Processor, those architectures are also readily supported by 
the Linux operating system. And sometimes packages

come, which are not tied to any particular 
architecture, because they may be a source code, are just pieces of files that are coming 
as a bundle, so they would be denoted with an architecture as noarch or all or src. 
So, look out for the string, which indicates the architecture for which the particular package 
has been built, and also which architecture your desktop mission is, so that you 
would install a compatible package. Usually, this is taken care by the package 
manager, so you do not have to worry much.
Let us look at what type of an architecture 
we see. You type a command, uname minus a, and you will see what type of a kernel is running 
right now, so my desktop is running kernel 5.11, and you could see some the string 
that is a x86 64 architecture. So, once you have identified which version of the 
Linux and what architecture then by and large,

you can actually pick up a package and install it yourself, but it is a good idea to go through the package management. So, here are some package management systems that are widely used across both the RPM type of package as well as Debian type of package. So, the so-called YUM software, which expands to Yellowdog Updater Modifier, is popularly used to manage the RPM packages. On Red Hat, you would have the RPM as an application which would help you manage the packages, and the YUM package management system would actually call RPM to install, update, or remove the RPM packages. In the recent past, the YUM package management system has been modified, and it is now called as DNF, which expands to Dandified YUM. So, if you have a Red Hat open system, then you would use DNF to manage the packages. Most of the options are quite compatible, so you should be able to readily use those commands.

However, we are going to learn in depth how to manage the Debian packages, which can be done both using a graphical user interface, as well as command line. So, synaptic is a graphical user interface, and aptitude is a command line interface available to manage packages of the type Debian, and at the backend is the advanced package tool, APT, which does the package management. And there is a tool called dpkg, which is called by APT to actually install the packages. So, we would also use some of the commands directly using dpkg, which further makes calls to dpkg hyphen, Deb, which we normally do not have to call directly ourselves. So, let us go and explore further Debian package management on Ubuntu our similar operating system using a APT and dpkg. So, we will now use the APT package management system to explore the packages on an Ubuntu operate system.

So, here are a few ways by which you can use the apt cache command, so you could search for a keyword, you could ask for what are the packages that have been installed on the operating system, and you could also ask for the detailed information of a particular package or a list of packages. So, let us look at these commands by actually running them on the command line. So, before we proceed, we should first check whether these comments are available, so that we would do by using the which command which apt. So, there is a file that is already available, so the apt is available for us to explore. So similarly, we would try apt cache that is available, and apt-get, so that is also available. So, we will now first explore the apt cache command, which does not require the super user permissions so directly, we can start using that. So apt, and then search, and you can give a keyword to search the packages that may have

that particular keyword in either the description 
or the title of that particular package. 
So, let us search for a package called fortune. 
And you will see that there is a lot of packages   which have that word. And you see that there is a 
package here called fortunes, which is basically   a data file containing a fortune cookies. So, it 
is something funny that it would display on the   screen, if you are under command fortune. 
Let us search for a string like nmap   to see what are the packages that have that 
particular keyword, and you will see that   there are many such packages, but the one which 
we may have in our mind is the network mapper   called nmap. And let us say somebody mentioned 
to us wget and we want to know what is it about,   and you will see, that there is definitely 
a package by the name wget which retrieves   files from the Internet. So, you could actually 
like that search for packages using a keyword and

then identify the specific package that you may be interested in knowing. Now, we have identified some packages now, so let us go and see whether we have those installed or not.

Let us see what are the packages that are installed on this particular system. So, we will do that by passing a keyword to the apt cache command pkgnames. And it would actually give a long list of packages that are installed, so we could actually then pipe it to the less command so that we could see the screen output page by page. So, you could see now that you could scroll through the list.

Now, you see that this list does not seem to have any sorting order, so we could also then use a sort to look at those page by page. So, you can now see that it has been sorted, so initially numerically after that alphabetically, so there are a lot of packages

that are installed on this particular system. If 
you want to avoid looking through the entire list,   but only those packages that are starting with 
a particular character or a set of characters,   you could also do that apt-cache pkgnames and 
then after that, you could start with let us say,   nm, and you will see that all those packages, 
which have the first two characters as nm will   be displayed, and then nmap is one of those 
packages that has been installed. So, we want   to know a little bit more about that package, 
so let us go ahead and ask apt-cache to show the   details of that particular package nmap.
So, you can now see that the details are   being displayed here. So, it says that this 
package is part of the AMD 64 architecture,   which is compatible with what we have. 
And this particular package has a name   for the file from the file that it has come 
from. The file that this package came from is

listed here. And if you look at the name, here, 
you can make out that it has a particular format. So, let us go and explore a little 
bit more about this format now. 
So, here you see the package name is 
given in a particular format, but the, and it is slightly different between the RPM and 
DEB. So, for the DEB format, you can see that the name of the package is followed by an underscore 
after that there is a version and a revision, and then there is an underscore and then the 
architecture dot deb. So, let us compare this with the file name that we just saw. 
So, the file name that we just saw is having two underscores. So, you can see that 
the string before the first underscore is the name of the package nmap and that you can 
already confirm here, and then you can see that the version is here so 7.80 plus df sg1 that 
is version 7.8 you can say that is a version,

and after the hyphen is the revision. 
So, 2build1 is a revision, so there are many revisions of a particular version that would come. And then after the second underscore is the architecture name, so AMD 64 is architecture. 
So, you can see that the file name of the package already gives you three pieces of information. The name of the package, the version, and the revision, as well as the architecture for which that particular package has been built. So, there are some more pieces of information that would come along, which we would explore now. 
So, each package also lists what kind of a priority that particular package is, and top was priority is required, which means it is essential to the proper functioning of the system. So, you should not remove that package unless you know what you are doing. And the second level of priority is important where it provides functionality.

which enables a system to run smoothly. It is a good idea to leave packages that are categorized as important also on the system. The third level of priority is standard, which means that these are the packages which came along with the standard system installation, but typically, if you have not done any specific customization to the installation then all operating systems of that particular version would contain those packages, which are at the level of priority called standard or higher than that namely important required. And then there are some packages, which are at the level of priority called optional, which, if you are running short of the storage, hard disk space is not enough, you could actually skip installing them or you can also delete them if you do not need them. And then there are some packages, which are called extra, so one has to pay a little attention to installing these software, because these are known to have certain

specialized required requirements, or could have 
conflict with packages, which are actually of higher priority. So, you should only install them 
if you really need them, and in the process, do not actually change the versions of the packages 
which are actually at a higher priority. So, one has to pay attention by installing these 
packages under the category extra. So, let us see some packages and identify where this 
particular piece of information is located. 
So, the output of the nmap package coming 
from the apt-cache shows the priority here. So, it says that it is an extra, that means, 
it is not very important. If you want, you can actually remove the package, and that does not 
hurt your system. So, let us look at some other package names and see what would it show. 
So, here is the information about the wget package, and it comes with a priority 
called standard, which means

that it is at a higher priority than nmap. 
And it is a good idea to keep the wget command, because it is a package that comes along with a 
standard installation of the operating system. 
  Let us look at the information about the fortune 
package. So, this package is under the optional category. So, which means that it does not have 
any conflict with the higher priority packages, so you can install it without having to pay 
extra attention, but it is an optional package, so if you want, you can delete it, in case 
your hard disk is running out of space. 
  So, what is this command for sure, let us 
just check it out and it then generally display something funny, some quotation, 
or sometimes it could be even harsh. So do not be offended. It is an entertainment 
for the programmer at the terminal and it will be different for every time that you type the same 
command. It is a randomly picked fortune cookie.

that you can display onto the screen. 
The Ubuntu packages also come categorized under package sections, and the list of sections 
will change depending upon the version. So, for the focal Linux, which is Ubuntu 20.04 lts 
here are the packet sections that are listed as per the website on ubuntu dot com. And you can see 
that the large number of categories under which the software packages have been grouped. So, we 
can actually see which package comes under which package section by looking at the output 
of the apt-cache show command. 
So, let us have a look at 
that now. So, the fortunes package comes under the section called universe 
slash games, so it a game so that is a category. You could also look at the category for nmap so it 
says that it comes under the universe by net so it is coming under the package group called net. 
And let us say wget that would be coming under the

section called web. So, like that, each of these packages comes under a particular section. So sometimes you may want to generally look at one of the packages in a particular section to even explore packages that you may not have heard of. So, you can look at the list of package sections, and there are some sections you may want to go thoroughly because you work in that particular topic or domain. For example, if you are fascinated by mathematics, then you may want to explore all the packages that are grouped under the package section called mathematics, and see that some of them actually may be quite interesting for you. You may not have come across those packages until you have looked at the listing here on the ubuntu dot com website. Now, how do we know that the package that we are installing on our operating system is an authentic one. So, the way to verify is by looking at what is called a checksum.

So, there are three major ways by which the 
checksums are computed. The first one is md5sum,   which gives you a 128-bit string, 
irrespective of the size of the input file,   and this would be very different even if there 
is a small change in the input string. 
  And then there is a SHA1 checksum, 
which is a 160-bit string, and then,   the most advanced that is being used today is 
the SHA256 checksum, which is a 256-bit string.   So, one can actually compare the check sums of 
any package with what is actually listed on the   ubuntu dot com website to see whether the package 
that has been installed or being installed is   authentic or not. In fact, there are more ways 
by which we can verify the authenticity, but   this is a very good opportunity for us 
to see what do these checksums mean. 
  So, let us explore that in a moment, let us 
explore the concept of checksums by using it.

on some files that we can create right on the 
command line, and we would use a simple string as the only content of the file to illustrate 
how the checksums can be very different for a small change done to the content of the file. 
So, we would echo a string to a file, so let us do that. This file is edited by, and then I give 
my name, and then I redirect the string to a file, file1 dot txt, and let me look at the 
file here. So, file1 dot txt has 35 bytes. Now, what I do is that I make a small change 
to this string, so what I would do is, instead of h I put n, and then write to another 
file called file2 dot txt. And now if you look at the files, the two files, file1 dot txt and 
file2 dot txt, are identical in their size.

And if we look at the contents, cat file1 dot 
txt and file2 dot txt, you could see that if you do not pay attention, they look identical. 
Except for the end and n, they look identical. But when we run the md5sum or any other 
sum that we have just not mentioned, you would see what is the difference. 
So, we now run md5sum of the file1 dot 
txt, and you see that you would get 128-bit string, and then we run it also for 
file2 dot txt, and you will see that the two strings are very different. So, it 
actually shows you that for a very small change in the bit sequence of the input stream, 
the output checksum is very different. And this 
is one way by which we can actually identify if 
the original file has been tampered or not. 
And there are other ways of evaluating the 
checksum, so let us look at those also.

So, sha1sum file1.txt, and sha1sum file2.txt. You could also see that the 160-bit string is very different between the two files, and then you also have sha256sum file1.txt, and sha256sum file2.txt. 
So, this would be a 256-bit string, which would also be very different if the input string is different or input stream file stream is different even in just a few bits. So, these are the three major mechanisms by which the checksums are compared to ensure that the file that is being installed is authentic and the same as what has been supplied by the original vendor of the software. And one has to pay attention to these while copying and to ensure that in the process of downloading, nothing has gone wrong to the contents of the file.

Software Management - Part 01

Software Management - Part 01