Is Root the same as supervisor mode??

xianzai · 05-23-2004, 05:40 PM

Hi all,

Quote:

An operating system relies on hardware to ensure protection of processes from each other.

Two different execution modi are required for hardware:

1: Kernel/Supervisor mode:

Allows unrestricted access to all resources.

2: User Mode

Only instructions not affecting others are allowed; sanity checks are enforced.

Is root the same as Kernel/supervisor mode, or am i getting confused?

Thanks!

M

Poetics · 05-23-2004, 05:55 PM

"root" is the superuser / supervisor / admin account, yes

xianzai · 05-23-2004, 06:21 PM

Sorry, thats not what I meant. I know root is the same as the super user account.

"Instructions only allowed in the supervisor mode are called privileged instructions..."

Is this true? Its for a degree course on operating systems.

btmiller · 05-23-2004, 07:18 PM

You're getting confused. Root is a user account on the machine, whereas supervisor mode is a state that the computer's CPU can be in, generally used only when executing the operating system. They're totally different worlds. Accounts and permissions are creations of the operating system, whereas different CPU execution modes vary based on the hardware (for instance, i386 CPUs actually have 4 different modes, but *nix systems only ever use two of them).

When you execute a program as root, such as ls, it still operates in user mode on the CPU. There would be no reason to switch the CPU into priviliged mode just to run ls, regardless if root or someone else started it. However, root can implictly run code on the CPU in supervisor mode, for instance by loading a kernel module. The module will run as part of the kernel, and the kernel runs in supervisor mode most of the time.