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git-svn-id: svn+ssh://atelier.inf.usi.ch/home/bevilj/group-1@192 a672b425-5310-4d7a-af5c-997e18724b81
78 lines
2.3 KiB
HTML
78 lines
2.3 KiB
HTML
---
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layout: page
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category-title: Intermediate commands
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category-page: intermediate
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tags:
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author: Andrea Brites Marto
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title: ps
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---
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<p>
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The <code>ps</code> command stands for "process status" and it is used to provide
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various information about the currently running processes.<br>
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Every process is an executing instance of a program which is assigned a unique PID
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(process identification numbers) by the system.</p>
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The basic syntax of <code>ps</code> is:
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<pre>
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ps [options]
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</pre>
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<p>
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This command can be used without any option and by doing this you will get the standard output,
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which is the display monitor by default with four items of information for at least two
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processes currently on the system: the shell and ps.<br>
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Since we have already saw PID before, the TTY information that stands for terminal type
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(originally teletype) is the console (or terminal) in which the user logged into.<br>
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TIME is very simple: is the amount of CPU time in minutes and seconds that the process
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has been running. CMD is simply the name of the command that launched the process.<br>
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Here you will find some common option combinations
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</p>
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<pre>
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ps -aux | less
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</pre>
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<ul>
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<li>The -a option is used to list the processes of all users on the system.</li>
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<li>The -u option tells ps to provide detailed information about each process.</li>
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<li>The -x option adds to the list, processes that have no controlling terminal
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(programs launched during booting).
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</li>
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</ul>
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<p>
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This can be piped to the less command ( see out section pipe), which let us to
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view all processes in one screenfull at a time.<br>
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Another way to view all processes running on the system is:
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</p>
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<pre>
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ps -ef | less
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</pre>
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Where:
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<ul>
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<li>The -e option is used to generate a list of information about every process
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(currently running).
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</li>
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<li>The -f option provides a list that contains some information for each process.</li>
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</ul>
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<p>
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This is very useful, it can be used for example to control UID information (username of
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the account that owns the process) and STIME to know when the process started, or
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the starting date.<br>
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In the end the <code>ps</code> is very powerful if we know how to use it.
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If you need to kill a process you can list all process in various ways
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and search for the process you need to kill by reading its PID or by UID for example.
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</p>
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