Let's say we have a large company X which stores private user information. For example an e-mail provider, or social network provider. I mainly have GMail and Facebook in mind. So the company has thousands of employees. Let's further suppose that X uses Linux for all their machines (from my understanding this is indeed the case with Google and Facebook for their server machines).
Now, from my understanding, X would usually have some data-centers which contain many server machines, and the user data would be stored on those machines. Let's say we have some machine with user-data on it. It may be encrypted when stored, but it should be decryptable if it is going to be returned to the user at some point. So it would seem like a sysadmin with sufficient access rights could access that user-data.
Now, I understand that in such a company most employees would not have access rights to user information, and those who do would be subject to logging of their access to resources. However, wouldn't there always be at least one person/sysadmin who has superuser access to a given machine? and such a person could access user information and also have control of the logging functionality on that machine, so would be able to do that without traces?
Is my analysis correct? I am mostly wondering if such companies who store user data, would have such sysadmins who have superuser access to user-data and logging and so would be able to retrieve user data without leaving traces?
If this analysis is correct, who would usually have such permission? would it be just some low-ranking sysadmin? maybe only the Chief Information Security Officer?
If the analysis is incorrect, how do they set-up a situation where there is no single person/insider that is able to abuse user-data in the way I described? Some ideas I have for how this could perhaps be done: (1) require authentication from more than one person. (2) keep the user-data on one machine, with one sysadmin, and the decryption key on a separate machine which has another sysadmin (so again it would require a collusion of two insiders to abuse the data)