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Do they? for example, I was thinking of the simple system call chown.
Does it call other system calls like read and write? How can we find out?
Kernel (e.g. Linux) has own internal system call interface, so one system call can usually call other system call, without need to setup the entire system call procedure.
How to find out? You have the kernel sources, you have probably grep, so you could find out.
Yes they do. For example the fork system call actually calls the clone system call. We can also use the clone system call for finer control over the child process.
fork() = clone(CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD)
Required, but never shown