Add more info about package managers

src/day_1/packages.md

@@ -34,7 +34,7 @@ After the installation is done, you can enter `cmatrix`. Congratulations, you ar
 
 To exit the matrix, press `q`.
 
-What if you don't like the matrix and want to remove it? You can uninstall packages using `sudo dnf uninstall PACKAGENAME`. In this case: `sudo dnf uninstall cmatrix`. You have to confirm again with `y`.
+What if you don't like the matrix and want to remove it? You can uninstall packages using `sudo dnf remove PACKAGENAME`. In this case: `sudo dnf remove cmatrix`. You have to confirm again with `y`.
 
 Why do we speak about _packages_ instead of programs when installing software on Linux? Because packages can contain more than one binary (the actual programs) and extra files. Take a look at [the files that are installed with `cmatrix` on Fedora](https://packages.fedoraproject.org/pkgs/cmatrix/cmatrix/fedora-rawhide.html#files) for example.
 
@@ -76,3 +76,91 @@ If you don't have access to `sudo` and try to use it, then you get an output lik
 > You might find a "meme" in the internet that tells you to run something like `sudo rm -rf /`. This command will delete EVERYTHING on your machine. It is like delete the `C` and all other drives at the same time on Windows.
 >
 > Linux assumes that you know what you are doing when you use `sudo`. With great power comes great responsibility!
+
+### Looking for a package
+
+If you don't exactly know the name of a package you are looking for, then you can use `dnf search PATTERN`. DNF will then return packages that match the pattern in their name or description.
+
+For example, if you search for Julia (which is a programming language, you get the following results):
+
+```console
+$ dnf search julia
+============================ Name Exactly Matched: julia ============================
+julia.i686 : High-level, high-performance dynamic language for technical computing
+julia.x86_64 : High-level, high-performance dynamic language for technical computing
+=========================== Name & Summary Matched: julia ===========================
+cantor-julia.i686 : julia backend for cantor
+cantor-julia.x86_64 : julia backend for cantor
+julia-common.noarch : Julia architecture-independent files
+julia-devel.i686 : Julia development, debugging and testing files
+julia-devel.x86_64 : Julia development, debugging and testing files
+julia-doc.noarch : Julia documentation and code examples
+perl-DateTime-Calendar-Julian.noarch : Julian Calendar support for DateTime.pm
+vim-syntastic-julia.noarch : A syntax checker for julia programming language
+============================== Summary Matched: julia ===============================
+jday.i686 : A simple command to convert calendar dates to julian dates
+jday.x86_64 : A simple command to convert calendar dates to julian dates
+perl-Date-JD.noarch : Conversion between flavors of Julian Date
+python3-jdcal.noarch : Julian dates from proleptic Gregorian and Julian calendars
+```
+
+If you know the name of the program but you don't know the name of the package that contains this program, use `dnf provides PROGRAMNAME`.
+
+If you want to install the program `trash` (no joke) that provides you with the functionality of a system trash (instead of completely deleting), then you can run this:
+
+```console
+$ dnf provides trash
+trash-cli-0.21.10.24-2.fc36.noarch : Command line interface to the freedesktop.org trashcan
+Repo        : fedora
+Matched from:
+Filename    : /usr/bin/trash
+
+trash-cli-0.22.4.16-1.fc36.noarch : Command line interface to the freedesktop.org trashcan
+Repo        : updates
+Matched from:
+Filename    : /usr/bin/trash
+```
+
+You can see that the name of the package is not the same as the name of the program. Using `provides` makes your life easier while looking for the package to install.
+
+If you did find a package but you want to get more information about it, you can use `dnf info PACKAGENAME`:
+
+```console
+$ dnf info julia
+Available Packages
+Name         : julia
+Version      : 1.7.3
+Release      : 1.fc36
+Architecture : i686
+Size         : 45 M
+Source       : julia-1.7.3-1.fc36.src.rpm
+Repository   : updates
+Summary      : High-level, high-performance dynamic language for technical computing
+URL          : http://julialang.org/
+License      : MIT and LGPLv2+ and GPLv2+
+Description  : Julia is a high-level, high-performance dynamic programming language
+             : for technical computing, with syntax that is familiar to users of
+             : other technical computing environments. It provides a sophisticated
+             : compiler, distributed parallel execution, numerical accuracy, and an
+             : extensive mathematical function library. The library, largely written
+             : in Julia itself, also integrates mature, best-of-breed C and Fortran
+             : libraries for linear algebra, random number generation, signal processing,
+             : and string processing.
+             : 
+             : This package only contains the essential parts of the Julia environment:
+             : the julia executable and the standard library.
+
+Name         : julia
+Version      : 1.7.3
+Release      : 1.fc36
+Architecture : x86_64
+(...)
+```
+
+You get too results for Julia that seem to be identical. The difference is the _architecture_. Normal computers usually have the `x86_64` architecture, so you should look for it. But it is nice to know that other architectures are also supported.
+
+If you have a problem with a package after an update, then you can try to use an older version. To do so, refer to the documentation of `dnf downgrade`.
+
+To run updates on your system, use `dnf upgrade`.
+
+For security reasons, it is important to run updates frequently! The updates installed using a package manager in Linux update the whole system and its programs. This means that you don't have to update your packages separately.