Last Sync: 2022-05-24 14:30:04

Operating Systems/The Kernel.md

@@ -43,4 +43,17 @@ During the context switch from CPU to user space, the kernel allocates memory. I
 
 ## Device drivers
 
-Devices are managed by the kernal and are not accessible directly via user space, since improper usage could crash the whole machine. There is little uniformity between devices and as a result drivers are needed. Thes are kernl code that enable different OS kernels to access and control the devices.
+Devices are managed by the kernal and are not accessible directly via user space, since improper usage could crash the whole machine. There is little uniformity between devices and as a result drivers are needed. Thes are kernl code that enable different OS kernels to access and control the devices.
+
+## System calls 
+Syscalls are what enable programs to start and are required for the acts of opening, reading and writing files. System calls in Linux are typically managed via C. 
+
+In Linux there are two particularly important system calls:
+
+* `fork()`
+  * When a process calls fork, the kernel creates a nearly identical copy of this running process
+* `exec()`
+  * When a process calls exec it passes a program name as a parameter. Then the kernel loads and starts this program, replacing the current process.
+
+Example with a terminal program like `ls`: 
+> When you enter `ls` into the terminal window, the shell that's running inside the terminal window calls `fork()` to create a copy of the shell, and then the new copy of the shell calls `exec(ls)` to run `ls`.