Now, who can install the packages in a Linux
operating system? The answer is the administrators. And in the case of Ubuntu, it would be called
a sudoers, that is, they could run a command as an administrator or a superuser. So, su for super user and do to execute, so
sudo a command can be executed by those who are listed in the file called etc sudoers. Now, even to actually view the file, it is
etc sudoers, you must be listed in that particular file. So, let us just check that out, and then,
we would go on to try how to install packages by actually running a demo. To install the software updates or new software
into the system, you will need to be a super user or an administrator. The superuser privileges are listed in a file
called slash etc slash sudoers, let us explored that using an example. Here I have a terminal in which I am logged
in as a guest.

So, I check who I am. So, I am logged in as a guest, and I can view the contents of the etc sudoers file only if I am actually present with those privileges in that particular file, and we can check whether we have those privileges or not. And when I run this, it would ask for the password, and let us say I make a mistake in giving the password, so there is a usual error that is for the password failure. But if you give it correctly, then it would go on to check whether the username is present in the sudoers list or not. And if the privileges are not sufficient, then there will be a message that you cannot actually proceed further. And there is also a message that the incident will be reported. So, what does it mean? It means that the administrator can find out that a regular user is trying to gain superuser privileges and has failed on a service that belongs to someone else. This could be a problem.

but if it is on your own machine, there is
nothing to worry. Let us check how does one find out whether
such a failure has happened. So, I will now come out of this particular
terminal, and I am now in the terminal where I am logged in as gphani, which is the regular
user for this machine, and also present in the sudoers list, and I can verify that now. I am logged into this terminal as gphani, which
will be the first user for this particular machine, and therefore also present in the
sudoers list. So, let me just check that out by looking
at the file contents of the sudoers. And it is asking me for the password, so I
give that properly, and then, if I am having that privilege, then it would be showing the
contents of the sudoers file, which is available in front of you now. And this file shows that apart from the root
user and myself, there is also one more user

who has the superuser privileges. Every other user will be denied permission
to install software on this particular mission. Now, what did we mean when we said that the
superuser can find out a failed attempt to have the superuser privileges by any other
user, so that would be available in a log file. And we know that most of the logs are kept
in /var/log/auth.log is the file where these events are reported so
we could look at the last 100 lines of this particular file. And again, this auth log is also only for
super users, so we go ahead and use the superuser privileges for that. And we now see that in the output, there is
an entry here saying that there is an authentication failure for the guest user and the message
is saying that user is not in the sudoers list. And later on, I was successful in becoming
a super user from the regular account, so you could also see that here, where it opens
the superuser permissions for a particular

user UID zero. So here you can see that the successful usage
of superuser privileges by the user gphani is documented, so the log book also tells
you who managed to gain the administrator privileges and who did not, and so one should
look at these logs time to time. So, when you are installing a package, the
system knows from which website these packages have to be downloaded for installation. So, where is this information stored? So, it is stored in a folder called /etc/apt/, so we will go there and explore that folder shortly. And there are two files that we have to look
up. The one is a folder called sources.list
and another is a directory called sources.list.d, in which there are different
entries, which come because you have added those sources for the Debian packages as a
part of a third-party software. For example, Google Chrome, or Microsoft Teams
or Zoom etc.

So, let us go to that folder /etc/apt. And you can see from here there are these files and sources.list is a file that we wanted to look at, so cat sources.list. And you can see here that most of these lines are actually comments because they start with the hash, but the ones with the do not have a comment character are the ones which are active. And you can see that here, the Debian packages are being fetched from a website called in.archive.ubuntu.com. The in this for India, so you would have this particular entry made during the installation of the Ubuntu operating system and it would be different for different countries so that Ubuntu would have a mirror that is closest to your country to fetch the packages. And here in this particular string, there is also the name of the version that you are going to use, and also certain other fields that would tell you which type of packages

are being held by that particular repository. And there are multiple repositories. So, you would have the main packages that
are there in one repository, and there is another repository in which updates are being
kept. And then sometimes there are also repositories
for source codes, so you could see here that there is a repository for the source code,
which is at this moment blocked out because the starting with a hash character, which
means, it has been commented out. So, this file is what contains the information
about which location the Debian packages are being fetched for installation on the system,
when you run commands to either install or update or upgrade the packages on your operating
system. Now, what about the folder sources dot list
dot d. So, sources dot list dot d, if you go to that
folder, then you can see that there are certain other entries. So, we would go and look at what is in the
Google Chrome. And you will see that there is a repository
that has been added, which is coming from

the Google website. So, dl dot google dot com is a website from
which the Debian package meant for the Google Chrome application are being fetched. So, the advantage of this is that whenever
Google upgrades the version of the Google Chrome, then the package management system
would automatically know the upgrade is available and would fetch the latest version and install
it on your operating system when you do the upgrade of the packages. So, that also means that you do not have to
worry, when is the next version available, it would be pushed to you through the package
management system as part of the apt update command that you would run, to fetch the updates
of all the packages that are installed on your system from the repositories that are
configured in these files. Like source dot list, or google chrome dot
list, etc. Now, let us see what do we mean by fetching
the updates. So, this is a command that you have to run
as a superuser, so sudo apt-get update.

What does it do when you run this command?
Is that it would actually contact the package management system. apt-get would contact the
repositories for any updates that are available for any of the packages, and then fetches
those updates and keeps them in the cache. And then when you want to upgrade the packages,
these updates are then applied depending upon which packages are actually installed on your
system. So, when you run sudo within a few minutes
of authenticating, then it will not ask for a password. But if quite some time has been elapsed, then
it would ask for the password again. As you can see that the updates are being
fetched from various repositories. And depending upon the network speed or the
network connectivity, it could take some time, and usually you would wait for it to finish
and return control back to you on the prompt. So, once you are done, it will also tell you
how much data has been fetched and at what speed etc.

And now the control is back to the prompt. So, what you could do now is to apply all
the upgrades that are available for the packages that have been installed till now. So, let us do that. It is a good habit to
do that every now and then. So, what I would do is that I will actually
do it every day. So, I try to keep the operating system up
to date with respect to all the versions that are given by the Ubuntu so that if there are
any security upgrades, then they will be available immediately. So, every now and then it is a good idea to
run this command sudo-apt get upgrade. So, first you run update to get the updates,
and upgrade to upgrade the packages. So, when you run this command, it would actually
list how many updates are going to be affected and how much of data is going to be downloaded. So, you could actually see that right now
the update is going to fetch 272 megabytes.

of data. So, sometimes if you are traveling and you
do not have a very good network connectivity, you may want to wait before doing the upgrade. So, keep an eye on this particular data. And then if it is okay to download that patch
of data, then you can go ahead and accept. So, the capital Y is for the accept, which is default,
so you can go ahead and just press Enter to accept the fetching all the updates. And depending upon the amount of data, the
patching of updates would take some time. So, wait patiently and let all the updates
be done so that your operating system is up to date. Every now and then, you will also have the
firmware upgrades from the Linux, which are very critical to ensure that the hardware
compatibility. When it says processing triggers, it means
that the downloading and installing is complete, and it is just finishing up certain actions
that are required upon installation of those particular upgrades. So, the control is back to the command prompt,
which means that the upgrades are done.

So, you could actually now check whether there are any further updates and upgrades, so you could run the commands once more. Usually, if there are no more updates pending, then it would just be done quite quickly. Now, it is also telling you to do some more action that is to auto remove, which means that there are some packages that came as a requirement for some other packages, and they are now no longer required because newer versions of those have been already installed, so you can actually save some space by removing those packages. And you are not telling which package to be removed, so you are leaving it to the package management system, which is a good idea, and it is saving me 494 megabytes of data on my disk because I am removing the unnecessary packages, which are of an older version. So, the control is back to the command prompt. So, the auto remove command has been completed. Now, you can actually look at the other operations also.

So, to remove a package and to add a package, and we would identify the fortunes package as one which we could play with because it is an optional utility which we can remove as our as per our wish. So, I am now trying to remove a package, and it is asking me to confirm, so we will do that and it goes on to remove that particular package. And once it removes the package, I should not have access to the command fortune, so let me remove the package called fortune mod, which contains the fortune cookies that are being displayed on the screen where I ran the command the fortune. So, I accept it. And now I will try to run the command fortune, and it says there is no such command, which means that the utility has been removed from the system. Now, I want to bring it back, all that I have to do is to install that package. So, I will do that right away, and there are no additional packages required and therefore

there is no confirmation being asked, and
the utility has been installed. And you could see that if I run the command,
then it works, and there is some fortune cookie that is being displayed on the screen. So, you could also do the reinstallation. So, you could also say, apt-get reinstall
package, so it would go ahead and then refresh the version. And sometimes we do it when there is any problem
with some of the utilities by mistake, we removed some configuration file of a particular
package, and we want to just fetch the package once more, and we could also do that using
the apt-get command. So, here are the utilities that we have tried
till now: apt-get update to synchronize the package overview files between the system
and the repository. And then to upgrade all the installed packages
to their latest versions, taking into account the conflicts, etc., apt-get upgrade will do
the job. And then you can install a package by simply
typing apt-get install package name.

And then if you want to reinstall it, you could also do that by using the command reinstall package. And all these commands will require sudo, as a prefix, because these operations will modify the operating system and therefore they are allowed only for the super users or administrators. So sudo permission is required for you to run these commands. Now, we have also done one more action, namely to remove packages that were automatically installed to satisfy a dependency, and not needed now because the packages have been upgraded beyond those versions, so you could save some disk space by removing those files and apt-get auto remove would do that for you. Now, you could also do one more action to clean up the disk by running the command apt-get clean. Normally, we do not do that because to revert back a particular version it may be okay to keep the retrieved package files. Sometimes you want to remove the package files and the configuration files, as well as the

original Debian package file to install that
package from your system, because you are running short of the storage of the hard disk,
and you could do that by using the purge command. We normally do not do that because we would
like to save bandwidth by keeping the package files in the system so that we could install
them readily when we need. Now, let us explore the dpkg package management
system, which is at a lower level, allows for installation of a package directly when you
download a deb file from the Internet. It is not recommended unless you know what
you are doing. Now, there is a directory that you would like
to explore to see some information about the packages, so we would go there and have a
look. So, var lib dpkg is a folder where text information
is available about various packages that are there on your system, so let us go there and
explore what is out there. So, we are here in var lib dpkg, and you see
that there are some files, so let us first

look arch file. So, it tells what are the architectures for
which the packages have been installed on this system. So, you could see that though my computer
is a 64-bit machine, I also have some 32-bit executables installed. This is for some library files that may be
required for compatibility reasons. And then there is a large file 181 kilobytes
which is called the available, so we would look at that by the less command. And you can see that it actually has a list
of the packages along with its full information one after the other, and this is one place
from where when you ask for information about a package, it will be taken out and shown
to you on the screen. You also have a file called status, which tells
you whether a particular package has been installed or not. Obviously, this file will be much larger than
available because the number of packages that you have installed will always be much less
than what are possible from the open to repository.

So, let us look at the status file, and you will see that whether it is installed or not. So, you can see the status here tells you whether it has been installed or not. And there is also a directory called info, and there you have got a set of files for each of the packages that are installed, and it would actually have also some information about the md5sum and such signatures that you may want to verify. So, let us explore files for a particular package, let us say wget, so, ls wget star, and you could see that there are three files. So, ls minus l, wget, so, you can then see what are those pieces of information that we have. So, more wget dot con files, and it will show you that there is one configuration file that comes along with the wget, which would be etc wget rc. And then wget dot list will tell you information of what all the files that would get copied.

onto the system when you install this package
called wget. And wget dot m5sums will actually show you
what all the md5sums of that of the files that have been installed on your system, and
you could actually now confirm whether some of them have been tampered by the system because
of unauthorized access to your system. And let us do that now. So, user bin wget has a particular md5sum,
so we would write md5sum some user bin wget, and you see that it matches with what is there
here. And this is something that we could actually
do to ensure that no executable or library in the system has been tampered compared to
file originally sent by the Ubuntu as a vendor of that particular software package. So, here are some utilities that we could
try by using the dpkg command where we could list all the packages, which match a particular
pattern because we are looking for the name of the package. We do not know the name exactly, so we start
with few characters and look for the names.

Also, we can see what all the files that came
with a particular package, or we can also see the status of a particular package, and we
can also search for a particular package from where a file has been installed. So, you know the name of the file, but you
do not know the name of the package from where it came, so you could also look up that by
using the minus capital S option of the dpkg command. So, let us look at these using a demo. So, dpkg with the minus option minus l, let
us say, and nmap as a keyword would actually see that there are no packages that have been
installed with that particular command. So, that means that I have not installed
that particular package yet. So, I will go ahead and install it. Now, that it is installed, I would go ahead
and run it again, and now you see that there is some information that comes up which tells
that this particular package has been installed.

and it has some information about the architecture
and the description, etc. The version, the name, and the revision, etc. So, all this information is available from
the dpkg command with a minus l option. Now, what are the various files that are provided
by this, you can actually check. So, you see that the nmap when you install
this package, these are all the various files that are being added to the system. So, you could see that user bin nmap is actually
coming from this package, but also nping, for example, or the man file coming from the nmap
also is here, for example. So, when you install a package, the manpage
is coming in and also certain other utilities bundled along with the particular main executable. And you would also see that the manpage is
coming with the multiple languages also. Now, you can actually find out the status
of a particular package by typing the minus s option.

So, it now says that yes, it is installed,
and what is the priority, and etc. So, this is the same output which comes from
apt-cache show command, and it is actually asking it to via the dpkg command on the backend. And it also gives you very detailed information
about that particular utility. And if you have asked that about any other
package, you will also know whether it has been installed or not. Now, let us say there is a particular executable
which you want to know which package has led to that particular executable being made available. And so, you could search for that by the commander
with a minus capital S option, and let us say the executable I want to look up is user
bin perl. So, it says that the perl base is the name
of the package from where this particular executable has come. So, which means that I could now go and look
at some more information about that particular package name because the package name is available.

So, dpkg minus the small s to show about the
package, and then here you see that information is available. It is an essential package comes into the
section called pearl. And you would see information about the particular
package, that is a scripting language used in many systems, scripts and utilities, so
you should not remove this particular executable or the package. And you would also see that it is maintained
by the Ubuntu developers directly. So, now you can see that we have learnt about
how to install packages, how to upgrade them, how to remove the packages, and how to fetch
updates about the packages and do an nmass updation of the packages on the system etc,
using two major systems apt as well as dpkg. Now, if we may want to search for all the
packages under a particular section or package section, and that for that we would actually
look up a very low-level command, and I will show that using a demo.

So, let us look at the manual page for dpkg-query. So, this is a low-level tool, which we do not normally use, but it is basically to query the dpkg database about all the packages. And here is something that we would like to learn: minus w, minus w is to show the list of packages, and let us also see one more option that we will be finding of use: minus f, that is a format in which we want the information to be shown. And what are the kinds of formats that are possible, you will also look at the fields which has, for example the section, so section is one of the fields that we could use, and some more fields are like, for example, the name of the package, binary colon package. So, by combining these pieces of information, we can actually ask the system to list the packages as well as their sections in a particular format by directly posing that query. So, let us do that here: minus f is giving the format, and the format I would give as

follows. So, I would like the section name to be there,
and then, I would also like the field, which is basically the binary colon package to be
there. And after that, I would like an enter symbol
to go to the next line. And if I run that, now, I would actually see
a list of all the sections and within each section, what are all the binary packages
that are installed in my system. So, you can see that the list is quite long. Now, whenever the list is quite long, you
know what to do. So, you can pipe it to less and then you can
go through them one by one. So, the first field is the name of the section
under which that particular package has been categorized by Ubuntu, and the next item is
the name of the package that has come under the particular section into the system upon
installation. Now, what we do is that we would like to go
through section by so that we need sort so

let us sort it, and after that go page by page. So, what are we doing here? So, we are running a query to list all the packages with a particular format, namely, the section has to be given after that the name of the package has to be given, after that a new line. And this listing has to be sorted, and then it has to be displayed page by page. So, you can see how we are actually using the terminal environment to look at the list of packages under the sections, as done by the Ubuntu operating system, and we are looking at it page by page. So, you can see that under the admin section, these are the various utilities that have been installed, and then under the developer section, these are the utilities. And you can see that there is a bunch of editors that have been installed. So, the liberoffice tools are all coming under the editors category, and the whole bunch

of fonts that have been installed. And there is a Java utilities that have been
installed on my machine, and you could also see that there are lot of library files that
have come into the system because they come along with the utilities that we installed. So, now, you see that there are also some
shells that have come up. So, you can see that apart from the bash shell,
we also have other shells like csh, dash, and ksh also have been installed. So, now you can see that you are looking at
the utility names under the categories, so you want to learn more shells, then you can
see how many shells have been installed and then go on to explore them separately that
is how you can actually explore tools, so, that you have not been looking for consciously. But now that they are available for you under
each category, then you can go through them to be thorough about all the utilities that
come under a particular category.

Now, we would like to also look at only those sections, which let us say command or a particular category. So, let us say shells. So, the way to do that is to filter the output. And for filtering the output, there is a command called a grep, which we will be learning shortly. But for now, I will just illustrate how nice it is actually giving you the output as. Now, you can see that we have filtered the output to only choose to display those lines which contain the word shells. And you could see that the list of utilities that come out of the category called shells are displayed. So, you can see that this grep command is quite powerful in filtering the output that is coming in to the pipe, and we will learn more about that shortly. So, here is what we have done using the dpkg minus a small l for looking up a pattern by which the packages are going to be looked up.

Then minus capital L to list the files that
came when you install the package. Minus small s to look at the status of the
particular package, and minus capital S to look at which package has brought that particular
file that you are looking for. Now, if you have downloaded a deb file, you
could also install it using the minus i option directly, but this is not a good idea because
it may have some dependencies which you will have to bother about yourselves. By default, use package management system pointing
to a reliable repository such as the Ubuntu itself or a reputed company, say Google, but
do not download Deb files from the internet from unknown sources and install them on your
system because in the worst case it could actually damage the operating system, and
sometimes it may also not just work because there are dependencies which may have conflicts
with existing libraries and utilities on your system so always leave these decisions to
the packaged management system, so that, the

process of installation upgradation will happen
smoothly. And it is not a good idea to remove a package
using this command because you maybe removing a package that is required by many other packages,
and therefore, removing packages should be also done using a package management system
like for example apt or synaptic or aptitude. With that, we come to the end of this session
on software management. Please do read the documentation for the package
management that is relevant for your operating system, say apt or dpkg for Ubuntu, or maybe
RPM or DNF for Red Hat Linux, or OpenSuSE Linux, etc., and make yourself comfortable with various
options so that you are on top of the software management of your computer. One of the important things about the stability
of Linux operating system is that almost everything that you would like is available from the
original maintainer of that particular flavor of Linux operating system, and in many ways,
when you install a package, the checks are done to ensure the compatibility with the
existing libraries, and therefore, the operating

system is generally stable if you follow the
standard practices for installation or upgradation of software packages. So, enjoy expanding your operating system
to have all the tools that you would ever want to have on your system to learn various
tools that are required for your work without having to worry about the compatibility issues. In situations when the compatibility issues
cannot be resolved, there are also alternative methods available on a Linux operating system,
such as through the snap or docker, and you could explore them as alternatives whenever
you are unable to install a particular version of a package, but usually that problem does
not arise as long as you are using a stable software management system such as apt.

Software Management - Part 02

Software Management - Part 02