Managing Software
Introduction
Most Linux distributions use
what's called a package manager to
handle the installation, upgrades, and
uninstalls of the software on a system.
The Ubuntu distribution uses a
package manager called dpkg and
a front-end called apt
(advanced package tool).
We will use apt to install,
update, and remove software
from our servers.
sudo
In order to use the package manager,
we will need
the sudo command.
The sudo command allows us to
"execute a command as another user"
(see man sudo).
By default,
the sudo command
"executes a command as the superuser"
(see man 8 sudo).
The name of the superuser account
is root.
This user can perform administrative tasks
that regular users cannot.
For security purposes,
regular accounts may not add, remove, or
update software on a system, nor
may they modify most files or directories
outside their home directories.
Using sudo allows regular users to
perform maintenance tasks on our systems
by executing commands as the root user.
Some consider this safer than logging
in as the root user.
Not all regular users can use
the sudo command.
On regular Ubuntu distributions,
users must belong to the sudo group
in order to run the sudo command.
The groups command will return
a list of groups that your account belongs to.
On the Ubuntu version used by the
Google Cloud Platform (GCP),
the group of interest is called google-sudoers.
The difference between the sudo group
on regular Ubuntu distributions and
the GCP version is that regular users in the
google-sudoers group are not prompted for
their password.
Down the line,
we will need to use the sudo command
to modify files, create directories, and
perform other maintenance tasks needed to
install and manage software.
In this lesson, we will use sudo along
with the apt commands to update our
systems and install software.
sudo syntax
The sudo command is simple to use.
When necessary,
we use sudo by pre-pending it to
the regular commands that we have already
learned.
In our home directories, for example,
we don't need to use sudo to
create a new directory with the mkdir
command.
Instead we type
mkdir data to create a new
directory/folder called data.
But outside our home directory,
for example, in the directory
/usr/local/bin,
we need to use sudo to do such things.
(This is why I used the sudo command
when I showed you how to copy the
Learn the Commandline programs to
/usr/local/bin.)
If I want to create a data directory
in /usr/local/bin, then
I have to use sudo at the beginning of
my command:
cd /usr/local/bin
sudo mkdir data
Or, without changing to that directory, I can just specify the full path:
sudo mkdir /usr/local/bin/data
Or if I want to create a file in some other directory outside my home directory, then I have to use sudo there, too:
cd /srv
sudo touch data.csv
Or, without changing to that directory, I can specify the full path:
sudo touch /srv/data.csv
apt
We will use sudo in the above
ways soon enough, but for now,
we will use sudo to install,
update, and uninstall software on
our systems.
Next I'll demonstrate the apt
commands that we'll need.
sudo apt update
Your system keeps a record of
what software is installed on your
system and their version numbers.
The sudo apt update command
updates that list and compares
the update to what's installed.
That is, if you have a piece of
software called acme1.1 on your system,
and acme1.2 is available, then
running sudo apt update will
let you know that you can upgrade to
acme1.2.
It's good practice to run sudo apt update
before installing or upgrading your system
because this lets your system upgrade to
the most recent version of what you want
to install.
In short, the command to download new package information is:
sudo apt update
sudo apt upgrade
Once the list of packages have been updated,
you can upgrade with the sudo apt upgrade
command if there are any upgrades.
When you run this command, and if
there are any upgrades,
you will be prompted to proceed.
You can press Y to proceed, or
N to cancel.
This command is simply:
sudo apt upgrade
apt search
If you want to install a piece
of software, then
you have to install it using its
package name.
Sometimes that means we have to
search for the name of the package.
This is one of the apt commands
that does not require the use of sudo.
sudo is not required because
apt search does not modify the system.
It simply helps you search for a package name.
For example, the man pages provide
helpful documentation about how to use
the commands on our systems, but
the man pages can also be dense and
not straightforward.
Fortunately, there's an application called
tldr that is a community-driven application
that provides simple help pages and examples
of how to use some of the most commonly used
commands.
To search for the tldr package,
we execute the following command:
apt search tldr
This returns a list of results that
match the search query.
One of those results is the tldr package,
which is simply named tldr.
Not all packages are simply named,
which is why we need to search for the
specific name.
Note that sometimes when we search for a package, the list of results is quite long. In those cases, pipe the above command through the
lesspager to page through the results:apt search <packagename> | less
apt show
If we want more specific information
about the package,
we can use the apt show command
along with the package name.
Therefore, to get more information
about the tldr application,
we execute the following command:
apt show tldr
This will return a fuller description
of the package (usually), as well
as the URL to the application's website,
plus other details.
We do not need to use sudo here
because we are not modifying the system.
We are only retrieving information.
sudo apt install
To install the tldr application,
we use the sudo apt install command
along with the package name.
We want to make sure that the name of the
package is exactly what was returned from
the apt search command.
In the tldr case,
it's pretty straightforward, and to install:
sudo apt install tldr
sudo apt remove
In order to remove a package,
we use the sudo apt remove
command.
I like to add the --purge option
because this also removes system configuration
files that I probably do not need.
That is, some applications
install configuration files (configs)
in the /etc directory.
Adding --purge will remove those configs.
To remove a package and its system configuration files (if any), we run the above command with the package name.
sudo apt --purge remove tldr
Some configs are stored in your home directory.
Generally only end user applications install
configs in our home directories.
The --purge option will not remove those configs;
instead, we have to remove them manually if we want.
sudo apt autoremove
One of the great things about dpkg and apt
is that it installs and handles software
dependencies really well.
Dependencies are other software that software
depends upon to run.
That is, few computer applications are self-contained, and
they often require other software to operate.
When we uninstall (or remove) applications,
the package manager does not auto uninstall those
dependencies that were installed with it.
We use the autoremove command to uninstall those,
which helps keep our systems clean:
sudo apt autoremove
sudo apt clean
When we install packages,
some files are installed with them.
The sudo apt clean removes those
extra files and frees up disk space.
It's a simple command:
sudo apt clean
Conclusion
The apt command makes it quite easy
to manage software on our systems.
We will use this command to install more
complicated software later.
Here's a list of commands we covered:
sudo apt updatesudo apt upgradeapt searchapt showsudo apt installsudo apt --purge removesudo apt autoremovesudo apt clean