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| <!-- %MENU% How to create processes and run other programs --> |
| <h2 class="chapter">26 Processes</h2> |
| |
| <p><a name="index-process-3147"></a><dfn>Processes</dfn> are the primitive units for allocation of system |
| resources. Each process has its own address space and (usually) one |
| thread of control. A process executes a program; you can have multiple |
| processes executing the same program, but each process has its own copy |
| of the program within its own address space and executes it |
| independently of the other copies. |
| |
| <p><a name="index-child-process-3148"></a><a name="index-parent-process-3149"></a>Processes are organized hierarchically. Each process has a <dfn>parent |
| process</dfn> which explicitly arranged to create it. The processes created |
| by a given parent are called its <dfn>child processes</dfn>. A child |
| inherits many of its attributes from the parent process. |
| |
| <p>This chapter describes how a program can create, terminate, and control |
| child processes. Actually, there are three distinct operations |
| involved: creating a new child process, causing the new process to |
| execute a program, and coordinating the completion of the child process |
| with the original program. |
| |
| <p>The <code>system</code> function provides a simple, portable mechanism for |
| running another program; it does all three steps automatically. If you |
| need more control over the details of how this is done, you can use the |
| primitive functions to do each step individually instead. |
| |
| <ul class="menu"> |
| <li><a accesskey="1" href="Running-a-Command.html#Running-a-Command">Running a Command</a>: The easy way to run another program. |
| <li><a accesskey="2" href="Process-Creation-Concepts.html#Process-Creation-Concepts">Process Creation Concepts</a>: An overview of the hard way to do it. |
| <li><a accesskey="3" href="Process-Identification.html#Process-Identification">Process Identification</a>: How to get the process ID of a process. |
| <li><a accesskey="4" href="Creating-a-Process.html#Creating-a-Process">Creating a Process</a>: How to fork a child process. |
| <li><a accesskey="5" href="Executing-a-File.html#Executing-a-File">Executing a File</a>: How to make a process execute another program. |
| <li><a accesskey="6" href="Process-Completion.html#Process-Completion">Process Completion</a>: How to tell when a child process has completed. |
| <li><a accesskey="7" href="Process-Completion-Status.html#Process-Completion-Status">Process Completion Status</a>: How to interpret the status value |
| returned from a child process. |
| <li><a accesskey="8" href="BSD-Wait-Functions.html#BSD-Wait-Functions">BSD Wait Functions</a>: More functions, for backward compatibility. |
| <li><a accesskey="9" href="Process-Creation-Example.html#Process-Creation-Example">Process Creation Example</a>: A complete example program. |
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