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<title data-rh="true">Practice exam B | mf</title><meta data-rh="true" name="viewport" content="width=device-width,initial-scale=1"><meta data-rh="true" name="twitter:card" content="summary_large_image"><meta data-rh="true" property="og:url" content="https://blog.mfocko.xyz/c/pexam/garbage_collect/"><meta data-rh="true" property="og:locale" content="en"><meta data-rh="true" name="docusaurus_locale" content="en"><meta data-rh="true" name="docsearch:language" content="en"><meta data-rh="true" name="docusaurus_version" content="current"><meta data-rh="true" name="docusaurus_tag" content="docs-c-current"><meta data-rh="true" name="docsearch:version" content="current"><meta data-rh="true" name="docsearch:docusaurus_tag" content="docs-c-current"><meta data-rh="true" property="og:title" content="Practice exam B | mf"><meta data-rh="true" name="description" content="Garbage everywhere…
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itemtype="https://schema.org/BreadcrumbList"><li class="breadcrumbs__item"><a aria-label="Home page" class="breadcrumbs__link" href="/"><svg viewBox="0 0 24 24" class="breadcrumbHomeIcon_YNFT"><path d="M10 19v-5h4v5c0 .55.45 1 1 1h3c.55 0 1-.45 1-1v-7h1.7c.46 0 .68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill="currentColor"></path></svg></a></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item"><a class="breadcrumbs__link" itemprop="item" href="/c/category/practice-exams/"><span itemprop="name">Practice Exams</span></a><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">Practice exam B</span><meta itemprop="position" content="2"></li></ul></nav><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><h1>Garbage Collection</h1>
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<div class="theme-admonition theme-admonition-caution admonition_xJq3 alert alert--warning"><div class="admonitionHeading_Gvgb"><span class="admonitionIcon_Rf37"><svg viewBox="0 0 16 16"><path fill-rule="evenodd" d="M8.893 1.5c-.183-.31-.52-.5-.887-.5s-.703.19-.886.5L.138 13.499a.98.98 0 0 0 0 1.001c.193.31.53.501.886.501h13.964c.367 0 .704-.19.877-.5a1.03 1.03 0 0 0 .01-1.002L8.893 1.5zm.133 11.497H6.987v-2.003h2.039v2.003zm0-3.004H6.987V5.987h2.039v4.006z"></path></svg></span>Exam environment</div><div class="admonitionContent_BuS1"><ul>
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<li>During the exam you will be provided with a barebone <em>exam session</em> on the
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<em>faculty computers</em>.</li>
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<li>In browser you are only allowed to have the following tabs open:<!-- -->
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<ul>
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<li><a href="https://en.cppreference.com" target="_blank" rel="noopener noreferrer">C documentation</a></li>
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<li>page containing the assignment</li>
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</ul>
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</li>
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<li>You <strong>are not</strong> allowed to use your own source code, e.g. prepared beforehand
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or from the seminars.</li>
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<li>You have <strong>5 minutes</strong> to read through the assignment and ask any follow-up
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questions should be there something unclear.</li>
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<li>You have <strong>60 minutes</strong> to work on the assignment, afterward your work will be
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discussed with your seminar tutor.</li>
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</ul></div></div>
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<p>You have gotten into a trouble during your regular upgrade of your archLinux<sup><a href="#user-content-fn-1" id="user-content-fnref-1" data-footnote-ref="true" aria-describedby="footnote-label">1</a></sup>
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installation… You've been carelessly running the upgrades for months and forgot
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about clearing up the caches.</p>
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<p>Your task is to write a program <code>garbage_collect</code> that will evaluate the shell
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history provided as a file and will try to find files or directories that are
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suspiciously big and decide which of them should be deleted to free some space.</p>
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<h2 class="anchor anchorWithStickyNavbar_LWe7" id="format-of-the-shell-history">Format of the shell history<a href="#format-of-the-shell-history" class="hash-link" aria-label="Direct link to Format of the shell history" title="Direct link to Format of the shell history"></a></h2>
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<p>You are provided one file consisting of the captured buffer of the terminal. You
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can see only two commands being used:</p>
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<ol>
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<li>
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<p><code>cd ‹somewhere›</code> that changes the current working directory.</p>
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<p>At the beginning you start in the root of the filesystem (i.e. <code>/</code>).</p>
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<p>You are <strong>guaranteed</strong> that <code>‹somewhere›</code> is:</p>
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<ul>
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<li><code>.</code> that is a current working directory (i.e. does nothing),</li>
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<li><code>..</code> that moves you up one level (in case you are in <code>/</code>, does nothing), or</li>
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<li>is a valid directory in the current working directory.</li>
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</ul>
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<div class="theme-admonition theme-admonition-caution admonition_xJq3 alert alert--warning"><div class="admonitionHeading_Gvgb"><span class="admonitionIcon_Rf37"><svg viewBox="0 0 16 16"><path fill-rule="evenodd" d="M8.893 1.5c-.183-.31-.52-.5-.887-.5s-.703.19-.886.5L.138 13.499a.98.98 0 0 0 0 1.001c.193.31.53.501.886.501h13.964c.367 0 .704-.19.877-.5a1.03 1.03 0 0 0 .01-1.002L8.893 1.5zm.133 11.497H6.987v-2.003h2.039v2.003zm0-3.004H6.987V5.987h2.039v4.006z"></path></svg></span>caution</div><div class="admonitionContent_BuS1"><p>There are no guarantees or restrictions on the names of the files or
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directories!</p></div></div>
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</li>
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<li>
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<p><code>ls</code> that will list files in the current working directory and their
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respective sizes. If there is a directory in the current working it has <code>dir</code>
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instead of the size.</p>
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</li>
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</ol>
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<div class="codeBlockContainer_Ckt0 theme-code-block" style="--prism-background-color:hsl(230, 1%, 98%);--prism-color:hsl(230, 8%, 24%)"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-text codeBlock_bY9V thin-scrollbar" style="background-color:hsl(230, 1%, 98%);color:hsl(230, 8%, 24%)"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">$ ls</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">dir a</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">14848514 b.txt</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">8504156 c.dat</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">dir d</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">$ cd a</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">$ cd .</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">$ cd .</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">$ cd .</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">$ ls</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">dir e</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">29116 f</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">2557 g</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">62596 h.lst</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">$ cd e</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">$ ls</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">584 i</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">$ cd ..</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">$ cd ..</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">$ cd d</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">$ ls</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">4060174 j</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">8033020 d.log</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">5626152 d.ext</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">7214296 k</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div>
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||
<p>For this input, you will get following file system:</p>
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<div class="codeBlockContainer_Ckt0 theme-code-block" style="--prism-background-color:hsl(230, 1%, 98%);--prism-color:hsl(230, 8%, 24%)"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-text codeBlock_bY9V thin-scrollbar" style="background-color:hsl(230, 1%, 98%);color:hsl(230, 8%, 24%)"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain">- / (dir, size=48381165)</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain"> - a (dir, size=94853)</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain"> - e (dir, size=584)</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain"> - i (file, size=584)</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain"> - f (file, size=29116)</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain"> - g (file, size=2557)</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain"> - h.lst (file, size=62596)</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain"> - b.txt (file, size=14848514)</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain"> - c.dat (file, size=8504156)</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain"> - d (dir, size=24933642)</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain"> - j (file, size=4060174)</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain"> - d.log (file, size=8033020)</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain"> - d.ext (file, size=5626152)</span><br></span><span class="token-line" style="color:hsl(230, 8%, 24%)"><span class="token plain"> - k (file, size=7214296)</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div>
|
||
<h2 class="anchor anchorWithStickyNavbar_LWe7" id="format-of-the-output">Format of the output<a href="#format-of-the-output" class="hash-link" aria-label="Direct link to Format of the output" title="Direct link to Format of the output"></a></h2>
|
||
<p>Your program should support 2 switches:</p>
|
||
<ul>
|
||
<li><code>-gt ‹min_size›</code> that will print out suspiciously big files.</li>
|
||
<li><code>-f ‹total_size› ‹min_unused›</code> that will print out a file to be deleted.</li>
|
||
</ul>
|
||
<h3 class="anchor anchorWithStickyNavbar_LWe7" id="-gt-min_size"><code>-gt ‹min_size›</code><a href="#-gt-min_size" class="hash-link" aria-label="Direct link to -gt-min_size" title="Direct link to -gt-min_size"></a></h3>
|
||
<p>With this switch you are provided one additional argument:</p>
|
||
<ul>
|
||
<li><code>min_size</code> that is the lower bound (inclusive) for size of any file or
|
||
directory that is supposed to be listed.</li>
|
||
</ul>
|
||
<p>When your program is being run with this switch, it is is supposed to print out
|
||
all files <strong>and</strong> directories that are bigger than the provided <code>min_size</code>.</p>
|
||
<h3 class="anchor anchorWithStickyNavbar_LWe7" id="-f-total_size-min_unused"><code>-f ‹total_size› ‹min_unused›</code><a href="#-f-total_size-min_unused" class="hash-link" aria-label="Direct link to -f-total_size-min_unused" title="Direct link to -f-total_size-min_unused"></a></h3>
|
||
<p>With this switch you are provided two additional arguments:</p>
|
||
<ul>
|
||
<li><code>total_size</code> that is a total size of the filesystem<sup><a href="#user-content-fn-2" id="user-content-fnref-2" data-footnote-ref="true" aria-describedby="footnote-label">2</a></sup>.</li>
|
||
<li><code>min_unused</code> that is a minimum of free space required for an upgrade.</li>
|
||
</ul>
|
||
<p>Your program should find <strong>exactly one</strong> file or a directory that is of the
|
||
smallest size, but big enough to free enough space for the upgrade to proceed.</p>
|
||
<p>In other words, if that file or directory is deleted, following should hold:</p>
|
||
<span class="katex-display"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML" display="block"><semantics><mrow><mrow><mi mathvariant="monospace">t</mi><mi mathvariant="monospace">o</mi><mi mathvariant="monospace">t</mi><mi mathvariant="monospace">a</mi><mi mathvariant="monospace">l</mi><mi mathvariant="monospace">_</mi><mi mathvariant="monospace">s</mi><mi mathvariant="monospace">i</mi><mi mathvariant="monospace">z</mi><mi mathvariant="monospace">e</mi></mrow><mo>−</mo><mrow><mi mathvariant="monospace">u</mi><mi mathvariant="monospace">s</mi><mi mathvariant="monospace">e</mi><mi mathvariant="monospace">d</mi></mrow><mo>≥</mo><mrow><mi mathvariant="monospace">m</mi><mi mathvariant="monospace">i</mi><mi mathvariant="monospace">n</mi><mi mathvariant="monospace">_</mi><mi mathvariant="monospace">u</mi><mi mathvariant="monospace">n</mi><mi mathvariant="monospace">u</mi><mi mathvariant="monospace">s</mi><mi mathvariant="monospace">e</mi><mi mathvariant="monospace">d</mi></mrow></mrow><annotation encoding="application/x-tex">\mathtt{total\_size} - \mathtt{used} \geq \mathtt{min\_unused}</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7063em;vertical-align:-0.0951em"></span><span class="mord"><span class="mord mathtt">total_size</span></span><span class="mspace" style="margin-right:0.2222em"></span><span class="mbin">−</span><span class="mspace" style="margin-right:0.2222em"></span></span><span class="base"><span class="strut" style="height:0.7719em;vertical-align:-0.136em"></span><span class="mord"><span class="mord mathtt">used</span></span><span class="mspace" style="margin-right:0.2778em"></span><span class="mrel">≥</span><span class="mspace" style="margin-right:0.2778em"></span></span><span class="base"><span class="strut" style="height:0.7063em;vertical-align:-0.0951em"></span><span class="mord"><span class="mord mathtt">min_unused</span></span></span></span></span></span>
|
||
<h2 class="anchor anchorWithStickyNavbar_LWe7" id="example-usage">Example usage<a href="#example-usage" class="hash-link" aria-label="Direct link to Example usage" title="Direct link to Example usage"></a></h2>
|
||
<p>You can have a look at the example usage of your program. We can run your
|
||
program from the shell like</p>
|
||
<p>$ ./garbage_collect shell_history.txt -gt 10000000
|
||
24933642 /d
|
||
14848514 /b.txt
|
||
48381165 /</p>
|
||
<p>$ ./garbage_collect shell_history.txt -f 70000000 30000000
|
||
24933642 /d</p>
|
||
<h2 class="anchor anchorWithStickyNavbar_LWe7" id="requirements-and-notes">Requirements and notes<a href="#requirements-and-notes" class="hash-link" aria-label="Direct link to Requirements and notes" title="Direct link to Requirements and notes"></a></h2>
|
||
<ul>
|
||
<li>Define <strong>structures</strong> (and <strong>enumerations</strong>, if applicable) for the parsed
|
||
information from the files.</li>
|
||
<li>For keeping the “records”, use some <strong>dynamic</strong> data structure.<!-- -->
|
||
<ul>
|
||
<li>Don't forget to consider pros and cons of using <em>specific</em> data structures
|
||
before going through implementing.</li>
|
||
</ul>
|
||
</li>
|
||
<li>You <strong>are not required</strong> to produce 1:1 output to the provided examples, they
|
||
are just a hint to not waste your time tinkering with a user experience.</li>
|
||
<li>If any of the operations on the input files should fail,
|
||
<strong>you are expected to</strong> handle the situation <em>accordingly</em>.</li>
|
||
<li>Failures of any other common functions (e.g. functions used for memory
|
||
management) should be handled in <strong>the same way</strong> as they were in the
|
||
homeworks and seminars.</li>
|
||
<li>Your program <strong>must free</strong> all the resources before exiting.</li>
|
||
</ul>
|
||
<section data-footnotes="true" class="footnotes"><h2 class="anchor anchorWithStickyNavbar_LWe7 sr-only" id="footnote-label">Footnotes<a href="#footnote-label" class="hash-link" aria-label="Direct link to Footnotes" title="Direct link to Footnotes"></a></h2>
|
||
<ol>
|
||
<li id="user-content-fn-1">
|
||
<p>Also applies to Fedora, but… we use arch btw <!-- -->😉 <a href="#user-content-fnref-1" data-footnote-backref="" aria-label="Back to reference 1" class="data-footnote-backref">↩</a></p>
|
||
</li>
|
||
<li id="user-content-fn-2">
|
||
<p>duh! <a href="#user-content-fnref-2" data-footnote-backref="" aria-label="Back to reference 2" class="data-footnote-backref">↩</a></p>
|
||
</li>
|
||
</ol>
|
||
</section></div><footer class="theme-doc-footer docusaurus-mt-lg"><div class="theme-doc-footer-edit-meta-row row"><div class="col"><a href="https://github.com/mfocko/blog/tree/main/c/pexam/b-garbage_collect.md" target="_blank" rel="noopener noreferrer" class="theme-edit-this-page"><svg fill="currentColor" height="20" width="20" viewBox="0 0 40 40" class="iconEdit_Z9Sw" aria-hidden="true"><g><path d="m34.5 11.7l-3 3.1-6.3-6.3 3.1-3q0.5-0.5 1.2-0.5t1.1 0.5l3.9 3.9q0.5 0.4 0.5 1.1t-0.5 1.2z m-29.5 17.1l18.4-18.5 6.3 6.3-18.4 18.4h-6.3v-6.2z"></path></g></svg>Edit this page</a></div><div class="col lastUpdated_vwxv"><span class="theme-last-updated">Last updated<!-- --> on <b><time datetime="2023-05-08T00:00:00.000Z">May 8, 2023</time></b></span></div></div></footer></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages"><a class="pagination-nav__link pagination-nav__link--prev" href="/c/category/practice-exams/"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">Practice Exams</div></a><a class="pagination-nav__link pagination-nav__link--next" href="/c/pexam/cams/"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">Practice exam C</div></a></nav></div></div><div class="col col--3"><div class="tableOfContents_bqdL thin-scrollbar theme-doc-toc-desktop"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#format-of-the-shell-history" class="table-of-contents__link toc-highlight">Format of the shell history</a></li><li><a href="#format-of-the-output" class="table-of-contents__link toc-highlight">Format of the output</a><ul><li><a href="#-gt-min_size" class="table-of-contents__link toc-highlight"><code>-gt ‹min_size›</code></a></li><li><a href="#-f-total_size-min_unused" class="table-of-contents__link toc-highlight"><code>-f ‹total_size› ‹min_unused›</code></a></li></ul></li><li><a href="#example-usage" class="table-of-contents__link toc-highlight">Example usage</a></li><li><a href="#requirements-and-notes" class="table-of-contents__link toc-highlight">Requirements and notes</a></li></ul></div></div></div></div></main></div></div></div><footer class="footer footer--dark"><div class="container container-fluid"><div class="row footer__links"><div class="col footer__col"><div class="footer__title">Git</div><ul class="footer__items clean-list"><li class="footer__item"><a href="https://github.com/mfocko" target="_blank" rel="noopener noreferrer" class="footer__link-item">GitHub<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li><li class="footer__item"><a href="https://gitlab.com/mfocko" target="_blank" rel="noopener noreferrer" class="footer__link-item">GitLab<svg width="13.5" 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