How to delete old packages installed by pacman in Arch Linux?

No, pacman doesn't remove old packages from your cache (/var/cache/pacman/pkg) so, over time, it can fill up.

You can adopt two approaches to clearing the cache: the brute force one with pacman -Sc:

-c, --clean
Remove packages that are no longer installed from the cache as well as currently unused sync databases to free up disk space. When pacman downloads packages, it saves them in a cache directory. In addition, databases are saved for every sync DB you download from, and are not deleted even if they are removed from the configuration file pacman.conf(5). Use one --clean switch to only remove packages that are no longer installed; use two to remove all files from the cache. In both cases, you will have a yes or no option to remove packages and/or unused downloaded databases.

Or, for a more nuanced approach, you can use one of the utilities that ships with pacman-contrib, paccache:

paccache is a flexible pacman cache cleaning utility, which has numerous options to help control how much, and what, is deleted from any directory containing pacman package tarballs.

By default, paccache -r will remove all but the last three versions of an installed package, but you can change this number with the -k, --keep switch. There is also a -d, --dryrun switch to preview your changes. You can also use the -m, --move <dir> option to move the packages to a separate directory of your choice. See paccache -h or paccache --help for all the switches.

There are a number of utilities in the pacman-contrib package to assist with package management, it is worth looking though them all and gaining an understanding of how they work and can make running Arch much easier. You can see the full list with:

pacman -Ql pacman-contrib | awk -F"[/ ]" '/\/usr\/bin/ {print $NF}'

Your package cache is in /var/cache/pacman/pkg/.

NOTE: pacman packages were updated in 2018 and additionally require installing pacman-contrib to use scripts/tools like paccache described below.

Do:

paccache -d

To do a -dryrun and see what a run of that utility might remove when you next do:

paccache -r

To remove cached packages. 17gbs does sound steep. Make sure you haven't got some run-away logs. Do:

du -h /var/log

Or even just:

du -h /var

For a more general idea of what's going on.

I strongly suggest the use of paccache instead of pacman -Sc. There is even a very effective flag for removing selectively the versions of uninstalled packages -u. The flags of paccache I recommend are (as part of paccache v5.0.2):

• -d, --dryrun: perform a dry run, only finding candidate packages
• -r, --remove: remove candidate packages
• -u, --uninstalled: target uninstalled packages only
• -k, --keep <num>: keep "num" of each package in the cache (default: 3)

Example: Check for remaining cache versions of uninstalled packages

paccache -dvuk0