[camuel]

Constructive criticism is always welcome.

The answer is that multi-tenant is different from multi-user on so many aspects.

Multi-user: 1. Usually closed institution or even single group within single institution where all know each other. 2. Usually a lot of shared data and application. 3. The risk of malicious activity is low. 4. The consequences of malicious activity are not severe/fatal. 5. Auditing followed by identification and penal actions are an effective strategy to stop malicious activity.

Multi-tenant: 1. Usually open to anyone without "background checks". 2. Single instance of malicious activity is severe, repeated malicious activity is fatal. 3. Auditing, identifying the intruder and suing him in court is not an effective strategy to stop malicious activities.

[ww520]

What I was talking about is the multi-user as a capability to run untrusted code. You were talking about it as a policy and procedure. The multi-user capability allows one to use permission to create a lock down, low privilege area to let anyone to run in it. There are open Unix accounts out there that allow anyone to log in to play around with it for a long time. The multi-tenant problem claim is just not a valid one.

[camuel]

If all is that simple & rosy why no hosting/cloud service uses it?

Why entire shared hosting industry custom-patches their kernel constantly with OpenVZ and stuff?

Why shared hosting has such a bad reputation for being insecure (despite all efforts).