LFS201 - Clarification Questions 1
It says when runnig a command in the command shell, it first forks a process from the parent, then a system call puts the parent to sleep.
Q: Where does that system call come from? Is it the command shell that forked the process or the child process?
Q: And is the fork initiated by the
It is really interesting, and I'm trying to understand it
A new process is created (forked from the user's login shell).
Ok, fork is a system call initiated by said login shell, correct?
A wait system call puts the parent shell process to sleep.
Is the wait system call initiated by the child or the parent process?
The command is loaded onto the child process's space via the exec system call. In other words, the code for the command replaces the bash program in the child process's memory space.
which process (child or parent) makes the exec system call?
The command completes executing, and the child process dies via the exit system call.
Is the exit system call something that is triggered in the child process code?
The parent shell is re-awakened by the death of the child process and proceeds to issue a new shell prompt.
The parent shell then waits for the next command request from the user, at which time the cycle will be repeated.
Next question: It says builtins are built into the shell code directly and do not involve loading programs, but when I run
which echo or
which kill I get that they are both in
Does that mean my specific system its not builtin? Or does builtin mean that the binaries for those are loaded directly into the process data or code or whatnot, i.e. that running builtins basically involve an
exec call as opposed to a
exec call from normal shell calls