Pacman

Archlinux's package manager.
You may also be insterested in arch ABS.

Documentation

archwiki pacman	https://wiki.archlinux.org/index.php/Pacman
archwiki PKGBUILD	https://wiki.archlinux.org/title/PKGBUILD
archwiki mirrors	https://wiki.archlinux.org/index.php/Mirrors
latest mirrorlist	https://archlinux.org/mirrorlist/?ip_version=4

Locations

/etc/pacman.conf	configure which repos to pull from (core, extra, communnity, multilib)
/etc/pacman.d/mirrorlist	configure which sources to pull from (waterloo, queensu etc)
/var/cache/pacman/pkg	currently installed programs. Can use these archives to rollback to older versions of program.
/var/log/pacman.log	history of pacman operations
/var/lib/pacman/db.lck	pacman lockfile

Notes

pacman usage

pacman configuration

pacman packages

pacman troubleshooting

Tips/Tricks

Downloading old Packages

Archlinux

Find the package you'd like to downgrade to here https://archive.archlinux.org/packages/.

Ex:

firefox https://archive.archlinux.org/packages   ## find url to package

pacman -U \
    https://archive.archlinux.org/packages/l/linux/linux-4.15.3-2-x86_64.pkg.tar.xz \
    https://archive.archlinux.org/packages/l/linux-headers-4.15.3-2-x86_64.pkg.tar.xz

WARNING:

Occasionally, you might need to install something to satisfy a current AUR package. But installing the core package will break the existing AUR package dependencies.

You have 2x options:

pacaur -S zfs-linux spl-linux -U https://...  https://..

Archlinux-Arm

# find cpu arch
uname -a

# download package for your arch
http://tardis.tiny-vps.com/aarm/packages/f/firefox/firefox-79.0.1-aarch64.tar.xz

# install
pacman -U firefox-79.0.1-aarch64.tar.xz