In fact, if factotum were implemented on Unix along with an analogue to the Plan 9 capability device, venerable programs like su and login would no longer need to be installed ‘‘setuid root.’’ — https://plan9.io/sys/doc/auth.html
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Plan9 has a completely different security model.
The Hostowner (usually Glenda) is essentially "root" and you're at the mercy of the filesystem regarding file privileges etc.
AFAIK there is no way to "become" glenda.