![]() That first line contains information about the background process - the job number and the process ID. Here, if the ls command wants any input (which it does not), it goes into a stop state until we move it into the foreground and give it the data from the keyboard. This displays all those files the names of which start with ch and end with. The simplest way to start a background process is to add an ampersand ( &) at the end of the command. The advantage of running a process in the background is that you can run other commands you do not have to wait until it completes to start another! If the background process requires any keyboard input, it waits. Background ProcessesĪ background process runs without being connected to your keyboard. While a program is running in the foreground and is time-consuming, no other commands can be run (start any other processes) because the prompt would not be available until the program finishes processing and comes out. The process runs in the foreground, the output is directed to my screen, and if the ls command wants any input (which it does not), it waits for it from the keyboard. This would display all the files, the names of which start with ch and end with. If you wish to list all the files in your current directory, you can use the following command − You can see this happen with the ls command. It gets its input from the keyboard and sends its output to the screen. When you start a process (run a command), there are two ways you can run it −īy default, every process that you start runs in the foreground. At any point of time, no two processes with the same pid exist in the system because it is the pid that Unix uses to track each process. Pids eventually repeat because all the possible numbers are used up and the next pid rolls or starts over. Each process in the system has a unique pid. The operating system tracks processes through a five-digit ID number known as the pid or the process ID. A process, in simple terms, is an instance of a running program. When you tried out the ls command to list the directory contents, you started a process. Whenever you issue a command in Unix, it creates, or starts, a new process. This environment contains everything needed for the system to run the program as if no other program were running on the system. ![]() ![]() When you execute a program on your Unix system, the system creates a special environment for that program. In this chapter, we will discuss in detail about process management in Unix.
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