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26 lines
1.1 KiB
HTML
26 lines
1.1 KiB
HTML
<header>Unix Processes</header>
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A process is simply a running program on your system. Your web browser,
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window manager, terminal window and X server are all processes that you
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interact with directly. Many other processes run in the background,
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such as web servers and other system tasks. A new process is created every
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time you type a command like <tt>ls</tt> or <tt>pwd</tt>, though such processes
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are typically short-lived. <p>
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Every process has a unique ID, called the process ID or PID. While every
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process running at any one time has a different ID, over time PIDs may be
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re-used. <p>
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Apart from the initial process (typically called <tt>init</tt>) each has a
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parent process from which it was created. For example, if you run <tt>vi</tt>
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from your shell prompt, <tt>vi</tt>'s parent process will be your shell.
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A process can have any number of children, but only one parent. <p>
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Each process runs with the permissions of some user and group, which apply
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when it accesses files and directories. Users and processes may only kill
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other processes that they own, with the exception of <tt>root</tt> who
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can kill anything. <p>
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<hr>
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