Q4OS is a new Debian based distribution aimed for low (and old) resources system and 32-bit based. For more info consult the site https://q4os.org/.
I don`t find the firewalld or firewall-cmd tool in Ubuntu!?
These higher level firewall tools are only present in Red hat distros, for Ubuntu or Debian like distribution
please look at ufw documentation.
Can I install Debian on top of another system in a directory (no virtualization)?
See the tool Debootstrap (https://wiki.debian.org/Debootstrap) .
How do I list the content of a Debian package?
$ dpkg –contents <package>
$ dpkg -c <package>
Can I clone the Ubuntu public repository?
Yes, with the tool apt-mirror.
Is there any Debian distro like without Systemd in 2019?
Sure: Devuan, Trisquel, Antix Linux and Mx Linux.
How do I downgrade a package in a Debian distribution?
To revert to the previous version of a Debian type package you follow these steps:
apt-cache show package_name
Then you specify the specific (previous) version you want to downgrade to
apt install packagename=version
How can I verify a package (check for modified configuration files or binaries) in a Debian like distribution (Debian, Ubunut, Mint, etc.)?
#dpkg -V <package_name>
How do I find to which Debian package a file belongs to?
$dpkg -S /path/to/file