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| <!-- %MENU% Writing the beginning and end of your program --> |
| <h2 class="chapter">25 The Basic Program/System Interface</h2> |
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| <p><a name="index-process-3002"></a><a name="index-program-3003"></a><a name="index-address-space-3004"></a><a name="index-thread-of-control-3005"></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. Though it may have multiple threads |
| of control within the same program and a program may be composed of |
| multiple logically separate modules, a process always executes exactly |
| one program. |
| |
| <p>Note that we are using a specific definition of “program” for the |
| purposes of this manual, which corresponds to a common definition in the |
| context of Unix system. In popular usage, “program” enjoys a much |
| broader definition; it can refer for example to a system's kernel, an |
| editor macro, a complex package of software, or a discrete section of |
| code executing within a process. |
| |
| <p>Writing the program is what this manual is all about. This chapter |
| explains the most basic interface between your program and the system |
| that runs, or calls, it. This includes passing of parameters (arguments |
| and environment) from the system, requesting basic services from the |
| system, and telling the system the program is done. |
| |
| <p>A program starts another program with the <code>exec</code> family of system calls. |
| This chapter looks at program startup from the execee's point of view. To |
| see the event from the execor's point of view, see <a href="Executing-a-File.html#Executing-a-File">Executing a File</a>. |
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| <li><a accesskey="1" href="Program-Arguments.html#Program-Arguments">Program Arguments</a>: Parsing your program's command-line arguments. |
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| <li><a accesskey="3" href="System-Calls.html#System-Calls">System Calls</a>: Requesting service from the system |
| <li><a accesskey="4" href="Program-Termination.html#Program-Termination">Program Termination</a>: Telling the system you're done; return status |
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