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<!--replace-end-7--><!--replace-end-4--><!--replace-end-1--></head><body><div class="ui fluid container universe"><!--replace-start-2--><!--replace-start-3--><!--replace-start-6--><div class="ui text container" id="zettel-container" style="position: relative"><div class="zettel-view"><article class="ui raised attached segment zettel-content"><div class="pandoc"><h1 id="title-h1">Devices</h1><p>Devices are hardware that require access to the CPU in order to function. Devices can either be external and plugged-in or internal to the motherboard. The most common type of device that you will work with are <span class="zettel-link-container errors"><span class="zettel-link" title="Wiki-link does not refer to any existing zettel"><a>Disks</a></span></span>.</p><p>Devices are files but they have some different capabilities than ordinaryq files. There are two types: <strong>block</strong> and <strong>stream</strong>. Device files reside in the <code>/dev/</code> directory.</p><p>Some of the most important device files are:</p><ul><li><code>hda</code> : a harddisk on a port</li><li><code>sda</code> : a harddisk on another port</li></ul><blockquote><p>Device files are an interface to a driver which accesses the hardware. A driver is therefore part of the Linux kernel.</p></blockquote><p>So when you see <code>sda</code> listed for example, this isn’t the harddisk itself, it is a file that communicates with a driver that controls how the kernel can interact with it. This is why when you add a new piece of hardware (such as a mouse for example) you have to install drivers (typically provided by the manufacturer) so that your kernel is able to interact with it and provide it with access to the CPU.</p><h2 id="listing-devices">Listing devices</h2><p>The following <code>ls</code> within the <code>/dev/</code> directory shows my main harddrive partitions:</p><pre><code class="language-none">brw-rw---- 1 root disk 259, 1 Jun 4 11:00 nvme0n1p1
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brw-rw---- 1 root disk 259, 2 Jun 4 11:00 nvme0n1p2
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brw-rw---- 1 root disk 259, 3 Jun 4 11:00 nvme0n1p3</code></pre><blockquote><p>Since device files are files we can interact with them using standard file programs like <code>ls</code> and <code>cat</code>.</p></blockquote><p>The <a href="File_permissions_and_execution_in_Bash.md#what-the-output-means">mode</a> is different from ordinary files. Each device file is prepended with <code>b, p, c, s</code> before the standard permissions. These stand for the major types of devices: <em>block, character, pipe</em> and <em>socket</em>.</p><dl>
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<dt>block</dt>
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<dd>Block devices transfer data as large fixed-size blocks. These are the most common device type and include harddrives and filesystems. As the data can be split up into discrete blocks of data, this facilitates quick random access from the kernel. </dd>
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<dt>character</dt>
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<dd>Character devices transfer data one character at a time.The data is not in discrete chunks, it is a continuous stream of characters. An example of a stream device file is a printer however many character devices (such as `/dev/null`) are not physically connected to the machine.</dd>
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<dt>pipe<dt>
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<dd>Pipe devices allow two or more processes to communicate with each other. They work in the same way as character devices (transferring data as a stream) but instead of the output being sent to a device, it is sent to another process.</dd>
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<dt>socket<dt>
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<dd>The same as pipe devices, facilitating communication between processes however they can communicate with many processes at once, not just a single process.</dd>
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<h2 id="devnull">/dev/null</h2><p><code>/dev/null</code> is a virtual device: it doesn’t actually exist as a piece of hardware on the system. It can be useful when <span class="zettel-link-container cf"><span class="zettel-link" title="Zettel: Redirecting to /dev/null"><a href="Redirect_to_dev_null.html">bash scripting</a></span></span> as a place to direct output that you don’t care about, for example errors or verbose program read-outs.</p><p>I like to think of <code>/dev/null</code> as being like earth in a circuit. It’s an outlet to safely dispose of things you are not interested in.</p><blockquote><p>! Make notes on this. Base on : <a href="https://linuxhint.com/what_is_dev_null/">https://linuxhint.com/what_is_dev_null/</a></p></blockquote></div></article><nav class="ui attached segment deemphasized backlinksPane" id="neuron-backlinks-pane"><h3 class="ui header">Backlinks</h3><ul class="backlinks"><li><span class="zettel-link-container cf"><span class="zettel-link"><a href="What_are_disks.html">What are disks?</a></span></span><ul class="context-list" style="zoom: 85%;"><li class="item"><div class="pandoc"><p>A disk is a mass storage <span class="zettel-link-container cf"><span class="zettel-link" title="Zettel: Devices"><a href="Devices.html">block_device</a></span></span> which we can write to and read from.</p></div></li><li class="item"><div class="pandoc">A disk is divided up into <span class="zettel-link-container errors"><span class="zettel-link" title="Wiki-link does not refer to any existing zettel"><a>Partitions</a></span></span> which are subsections of the overall disk. The kernel presents each partition as a <span class="zettel-link-container cf"><span class="zettel-link" title="Zettel: Devices"><a href="Devices.html">block device</a></span></span> as it would with an entire disk.</div></li></ul></li></ul></nav><nav class="ui attached segment deemphasized bottomPane" id="neuron-tags-pane"><div><span class="ui basic label zettel-tag" title="Tag">Linux</span><span class="ui basic label zettel-tag" title="Tag">computer-architecture</span></div></nav><nav class="ui bottom attached icon compact inverted menu blue" id="neuron-nav-bar"><!--replace-start-9--><!--replace-end-9--><a class="right item" href="impulse.html" title="Open Impulse"><i class="wave square icon"></i></a></nav></div></div><!--replace-end-6--><!--replace-end-3--><!--replace-end-2--><div class="ui center aligned container footer-version"><div class="ui tiny image"><a href="https://neuron.zettel.page"><img alt="logo" src="https://raw.githubusercontent.com/srid/neuron/master/assets/neuron.svg" title="Generated by Neuron 1.9.35.3" /></a></div></div></div></body></html>
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