[plug] Query related to kernel mode and UML

[Leon Brooks]

On Tue, 20 Apr 2004 15:13, Parag Nemade wrote:
> when i run a simple C program i am in kernel mode or
> in user mode?

User.

> when system call is called in a C program in which
> mode i am ?

The short answer is, you are in kernel mode. To answer this one fully 
takes a long time.

> Also what is User Mode Linux(UML). what is difference
> between UML and Simple LINUX KERNEL?

UML runs more or less as a program under a standard Linux kernel. 
Programs run from it are clients of a client.

> When i modify kernel and add some functions in kernel
> and boot it? my functions runs in kernel mode or user
> mode?

Short answer is kernel mode. Long answer is as before, very long.

> Is there any connection of modification of kernel to
> UML?

UML is good for modifying the kernel and trying out your modifications 
without such a great risk of doing something irreversible to your 
uptime (or filesystems). It's also useful as a "poor man's SElinux" or 
"super-chroot", for putting each user or service into its own separate 
virtual cage.

Cheers; Leon