After reading a lot of articles, I heard SELinux is a great way to tighten the security. So I decided to install SELinux and I used below command:

pranav@inspiron-5548:~$ sudo apt-get install selinux

[sudo] password for pranav: 

Sorry, try again.

[sudo] password for pranav: 

Sorry, try again.

[sudo] password for pranav: 

Reading package lists... Done

Building dependency tree       

Reading state information... Done

The following additional packages will be installed:

  policycoreutils selinux-policy-dummy

  selinux-utils

The following packages will be REMOVED:

  apparmor gnome-software-plugin-snap snapd

The following NEW packages will be installed:

  policycoreutils selinux selinux-policy-dummy

  selinux-utils

0 upgraded, 4 newly installed, 3 to remove and 0 not upgraded.

Need to get 544 kB of archives.

After this operation, 65.1 MB disk space will be freed.

Do you want to continue? [Y/n] y

Get:1 http://archive.ubuntu.com/ubuntu cosmic/universe amd64 selinux-utils amd64 2.8-1build1 [81.9 kB]

Get:2 http://archive.ubuntu.com/ubuntu cosmic/universe amd64 policycoreutils amd64 2.8-1 [450 kB]

Get:3 http://archive.ubuntu.com/ubuntu cosmic/universe amd64 selinux all 1:0.11 [11.2 kB]

Get:4 http://archive.ubuntu.com/ubuntu cosmic/universe amd64 selinux-policy-dummy all 0.1 [1,730 B]

Fetched 544 kB in 3s (211 kB/s)                  

Preconfiguring packages ...

(Reading database ... 193413 files and directories currently installed.)

Removing gnome-software-plugin-snap (3.30.2-0ubuntu8) ...

Removing snapd (2.37.1+18.10) ...

Removing apparmor (2.12-4ubuntu8) ...

Selecting previously unselected package selinux-utils.

(Reading database ... 193322 files and directories currently installed.)

Preparing to unpack .../selinux-utils_2.8-1build1_amd64.deb ...

Unpacking selinux-utils (2.8-1build1) ...

Selecting previously unselected package policycoreutils.

Preparing to unpack .../policycoreutils_2.8-1_amd64.deb ...

Unpacking policycoreutils (2.8-1) ...

Selecting previously unselected package selinux.

Preparing to unpack .../selinux_1%3a0.11_all.deb ...

Unpacking selinux (1:0.11) ...

Selecting previously unselected package selinux-policy-dummy.

Preparing to unpack .../selinux-policy-dummy_0.1_all.deb ...

Unpacking selinux-policy-dummy (0.1) ...

Processing triggers for mime-support (3.60ubuntu1) ...

Processing triggers for desktop-file-utils (0.23-3ubuntu3) ...

Setting up selinux-utils (2.8-1build1) ...

Processing triggers for bamfdaemon (0.5.3+18.04.20180207.2-0ubuntu1) ...

Rebuilding /usr/share/applications/bamf-2.index...

Setting up selinux-policy-dummy (0.1) ...

Processing triggers for systemd (239-7ubuntu10.8) ...

Processing triggers for man-db (2.8.4-2) ...

Processing triggers for gnome-menus (3.13.3-11ubuntu2) ...

Setting up policycoreutils (2.8-1) ...

selinux-autorelabel-mark.service is a disabled or a static unit, not starting it.

Setting up selinux (1:0.11) ...

Sourcing file `/etc/default/grub'

Generating grub configuration file ...

Found linux image: /boot/vmlinuz-4.18.0-16-generic

Found initrd image: /boot/initrd.img-4.18.0-16-generic

Found linux image: /boot/vmlinuz-4.18.0-15-generic

Found initrd image: /boot/initrd.img-4.18.0-15-generic

Found Windows Boot Manager on /dev/sda2@/EFI/Microsoft/Boot/bootmgfw.efi

Adding boot menu entry for EFI firmware configuration

done

update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults

Processing triggers for systemd (239-7ubuntu10.8) ...

Processing triggers for initramfs-tools (0.131ubuntu15.1) ...

update-initramfs: Generating /boot/initrd.img-4.18.0-16-generic

And then restarted my computer. The following images appear:

First thing that appears

Second image

Note that this machine is dual booted with Windows 10.

After adding selinux=0 in the grub menu, I was able to gain back my PC running.

What am I missing here? What should I do? Should uninstall SELinux?