Unlink core system binaries from Brew

[ledif]

It's relatively easy to accidentally pull in a separate systemd or dbus using brew when installing an application. I have done this before with brew install age-plugin-yubikey. In such cases, the first systemctl available in users' $PATH is from brew, which can cause some issues due to the mismatch in Brew's systemd vs the system's systemd.

Because of this, it would make sense to add a brew unlink systemd and brew unlink dbus to one of the startup services.

[ledif]

From @tulilirockz on Discord:

we probably just want to add brew to the PATH with lower priority
instead of putting it so early on the path

[castrojo]

What about just unlinking them right after an upgrade? Like add it to the upgrade service?

[renner0e]

What about just unlinking them right after an upgrade? Like add it to the upgrade service?

/etc/systemd/system/brew-upgrade.service.d/override.conf

[Service]
# Prevent Brew from overriding important system binaries like:
# systemctl, loginctl, dbus-*
ExecStartPost=/usr/bin/bash -c "/home/linuxbrew/.linuxbrew/bin/brew unlink systemd dbus"

This works for me on Bazzite and Aurora.