corso per ccna

corso per ccna.the process run in the background (with the & character) is the same as telling UNIX,to perform other tasks in the shell while the process is running. Here's how to get the program "cisco" to run as a background process.#The program ciscowill execute inthebackground . /cisco & .... The following processes may run on UNIX systems. The program ciscowill execute inthebackground .The init process.The orphan process ozombie process oThe daemon process.This section will briefly introduce the above processes, and the daemons will be covered in detail later in this chapter, as the SECFND exam covers some important concepts of daemons. Processes are started in a ready state and eventually switch to a running state when they execute, which is called process scheduling (processscheduling). o Process scheduling plays a critical role in ensuring that the CPU is running at full capacity, providing the shortest response time for all programs, and preventing system crashes. To achieve process scheduling, two different scheduling strategies are used to move processes in and out of the CPU following certain rules. o The first is non-preemptive scheduling, where the resources of the executing process give up the use of the CPU. The second is preemptive scheduling, in which the operating system decides that another process has a higher priority and causes it to preempt the CPU usage of the currently running process.Processes can have a parent/child relationship with each other. A childprocess is a process that is created by some other process at runtime. Child processes are generally created to perform a task within an existing process (also called the parent process). The parent process uses the fork system call to create the child process. Usually, a shell called the parent process is created, and the child process executes within it. The fork command is described in the next section. As the reader will soon learn, all UNIX processes, except the init process, have a parent process. The system assigns each process an integer as its identifier, called a process identifier (PID). The system assigns a PID value of 0 to the process schedule (commonly known as sched), and as seen in Figure 9.1, the system assigns a PID to each process.When the system boots, the kernel creates a special process called init, the "parent of all processes", which has the corresponding program file /sbin/init, which means that the init process has no parent. The init process is another name for the schedule process, so its PID is 1. Figure 9.2 shows the parent processes created by the init process, and the child processes created by these parents.