The user-space application is of no value if it cannot make service requests to the kernel, as it is not able to even terminate properly without asking the kernel to terminate the process it is running in. All system calls may be categorized as follows:

• Process control: System calls that fall into this category are responsible for the creation of processes/threads and their management, as well as memory allocation/deallocation
• File management: These system calls are responsible for file creation, deletion, and IO
• Device management: This category contains system calls used for device administration/access
• Maintenance: This category contains system calls for management of date, time, and files or device attributes
• Communication: Management of communication channels and remote devices