Apt/DPKG

Cheatsheet

Taking inventory
List installed packages	`apt list –installed`
List installed packages	`dpkg-query -l`
Finding files/packages
Show files from installed package	`dpkg -L [PACKAGE]`
Show installed package providing a file	`dpkg -S [PATHTOFILE]`
Show any package that would provide a file	`apt-file find [FILE]`
Show contents of .deb file	`dpkg –contents [DEBFILE]`
Downgrading/Installing particular versions
Check out available versions	`apt-cache showpkg [PACKAGE]`
Install particular version	`apt install [PACKAGE]=[VERSION]`
Marking
Mark as automatically installed	`apt-mark auto [PACKAGE]`
Mark as manually installed	`apt-mark manual [PACKAGE]`
Hold currently installed version	`apt-mark hold [PACKAGE]`

E.g., for Debian bookworm, add

deb http://deb.debian.org/debian bookworm-backports main contrib non-free

Add these lines:

deb http://deb.debian.org/debian testing main contrib
deb http://deb.debian.org/debian unstable main contrib

Create a new file in /etc/apt/apt.conf.d/, i.e. 80testing
Insert this to make stable the default source for packages (unless you want the entire system on testing):
```
APT::Default-Release "/^bookworm(|-security|-updates)$/";
```
Take note which mainline repositories you have actually included. You wouldn't want to miss bookworm-security, for example.