Process Creation

By: Jesse Miller

Operating systems need some way to make sure all the necessary process exist. In very simple systems, or in systems designed for running only a single application, it may be possible to have all the process that will ever be needed be present when the system comes up.

In general-purpose systems, however, some way is needed to create and terminate. In general-purpose systems, however, some way is needed to create and terminate processes as needed during operation.
There are four principal events that cause processes to be created they are system initialization, execution of a process creation system call by a running process, a user request to create a new process, and initiation of a batch job. When an operating system is booted, typically several processes are created.

Some of these are foreground processes, that is, processes that interact with users and perform work for them. Others are background processes, which are not associated with particular users, but instead have some specific function. One background process may be designed to accept incoming email, sleeping most of the day but suddenly springing to life when email arrives.

Another background process may be designed to accept incoming requests for WebPages hosted on that machine, waking up when a request arrives to service the request. Process that stay in the background to handle some activity such as email, WebPages, news, printing, and so on are called daemons.

Large systems commonly have dozens of them. In UNIX, the ps program can be used to list the running processes. In windows task manager is used.

In addition to the processes created at boot time, new processes can be created afterward as well. Often a running process will issue system calls to create one or more new processes to help it to do its job. Creating new processes is particularly useful when the work to be done can easily be formulated in terns of several related, but otherwise independent interacting processes.
In interactive systems, users can start a program by typing a command or clicking an icon.

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Taking either of these actions starts a new process and runs the selected program in it. In command based UNIX systems running X windows; the new process takes over the window in which it was started. In both systems, users may have a window, but it can create one and most do. A mouse can interact with the process.

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