According to https://wiki.archlinux.org/title/System_maintenance#Partial_upgrades_are_uns... pacman -Sywu is not safe. But pacman -Syu is safe. Quoting the wiki, the rational is that pacman -Sywu will update the pacman sync database without installing the newer packages. What I fail to see is why pacman -Sywu, followed by pacman -Su, 1. Will update the pacman sync database without installing the newer packages. But then 2. Will not update the pacman sync database while installing the packages it has prevoiusly downloaded. If `-Sywu` is *immediately* followed by `-Su` then there is no risk of running into a partial upgrade, but:
1) Then there is normally no reason to run those as separate commands, as `-Sywu` immediately followed by `-Su` has no benefits compared to simple `-Syu`. `-Sywu` is used to avoid the update, but download package files to the cache. 2) You are mentioning a system timer, so I assume `-Sywu` is not immediately followed by `-Su`. Unless you are also running unattended updates, which is even worse and *will* eventually break your system. `checkupdates -d` does exactly the same as `-Sywu`, but without updating the system-wide sync databases. So pacman’s view of everything remains the same as if nothing was updated. It only gets package files in the cache.