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Post on rm -rf rickrolling
2016-07-28 13:52:26 +00:00
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<h1 class="post-title" itemprop="name headline">How to rickroll people that try to run "rm -rf" on your system</h1>
<p class="post-meta"><time datetime="2016-07-28T16:00:00+02:00" itemprop="datePublished">Jul 28, 2016</time></p>
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<p><strong>WARNING: The method showed here could not prevent the actual execution of “rm -rf” if the “UNIX vandal” is clever enough. Proceed at your own risk, and make backups!</strong></p>
<p>I like Rick Astley late 80’s songs, and you can see them here in my Spotify:</p>
<p><img src="https://dl.dropboxusercontent.com/s/t9vywa4yjotxv0o/Screenshot_20160728_154506.png?dl=0" alt="dQw4w9WgXcQ" /></p>
<p>I like rickrolling people myself too, especially if they’re trying to delete my entire <code class="highlighter-rouge">/home</code> directory or, even worse, <code class="highlighter-rouge">/</code>. Since I learned how to use the <code class="highlighter-rouge">alias</code> built-in, I wanted a way to prevent that random people tinkering with my laptop (that I may forgot to lock) could delete potentially important stuff, just for fun or boredom.</p>
<p>The method that I’ll show will lock any <code class="highlighter-rouge">rm</code> command runned in both recursive and force mode, so <code class="highlighter-rouge">rm -rf</code>, <code class="highlighter-rouge">rm -f -r</code> and <code class="highlighter-rouge">rm -r --force</code> are all blocked, even if they are launched by <code class="highlighter-rouge">sudo</code>. I’m going to alias the rm command in <code class="highlighter-rouge">/etc/profile</code> <code class="highlighter-rouge">/etc/bash.bashrc</code> and in <code class="highlighter-rouge">/etc/zsh/zshrc</code> (I’m a zsh user) so that the rickroll will be possible from all users, even root and the ones with a brand new <code class="highlighter-rouge">bashrc</code> or <code class="highlighter-rouge">zshrc</code>. Here is the code I appended to those files:</p>
<figure class="highlight"><pre><code class="language-bash" data-lang="bash"><span class="nb">alias </span><span class="nv">rm</span><span class="o">=</span>/bin/rmAlias
<span class="nb">alias </span><span class="nv">sudo</span><span class="o">=</span><span class="s1">'sudo '</span> <span class="c"># this enables aliases in sudo, see http://askubuntu.com/questions/22037/aliases-not-available-when-using-sudo</span></code></pre></figure>
<p>Since <code class="highlighter-rouge">alias</code> is not able to control flags of the aliases (see <a href="http://apple.stackexchange.com/questions/50963/how-do-i-add-a-flag-to-an-alias">here</a>), we’re going to redirect each call of <code class="highlighter-rouge">rm</code> to <code class="highlighter-rouge">/bin/rmAlias</code>, that would run the command if it’s safe. I didn’t use a function because it’s a bit tricky to make that work with <code class="highlighter-rouge">sudo</code>. So, let’s see the code I put in <code class="highlighter-rouge">rmAlias</code>:</p>
<figure class="highlight"><pre><code class="language-bash" data-lang="bash"><span class="c">#! /bin/bash</span>
<span class="c"># Rickroll whoever tries to desert this system, even root.</span>
<span class="c"># To achieve this, set the appropriate aliases even in /etc/profile and similars.</span>
<span class="c"># Video played when rickrolling</span>
<span class="nv">ROLLVIDEO</span><span class="o">=</span>/opt/anti-rm/serious-video.mkv <span class="c"># it's just Never Gonna Give You Up on my system, but be free to customize this!</span>
rickroll<span class="o">(){</span>
<span class="nb">echo</span> <span class="s2">"Never gonna desert this system..."</span>
xdg-open <span class="nv">$ROLLVIDEO</span> 2&gt;&amp;1 &amp;
<span class="nb">exit </span>0
<span class="o">}</span>
<span class="k">while </span><span class="nb">getopts</span> <span class="s2">":rf-"</span> opt; <span class="k">do</span>
<span class="c"># Prevent '--force' to be detected as -r and -f</span>
<span class="k">if</span> <span class="o">[</span> <span class="s2">"</span><span class="nv">$opt</span><span class="s2">"</span> <span class="o">=</span> <span class="s2">"-"</span> <span class="o">]</span>; <span class="k">then
</span><span class="nv">OPTIND</span><span class="o">=</span><span class="nv">$OPTIND</span>+1
<span class="k">continue
fi
if</span> <span class="o">[</span> <span class="s2">"</span><span class="nv">$opt</span><span class="s2">"</span> <span class="o">=</span> <span class="s2">"r"</span> <span class="o">]</span> <span class="o">||</span> <span class="o">[</span> <span class="s2">"</span><span class="nv">$opt</span><span class="s2">"</span> <span class="o">=</span> <span class="s2">"f"</span> <span class="o">]</span>; <span class="k">then
if</span> <span class="o">[</span> <span class="s2">"</span><span class="nv">$tmp</span><span class="s2">"</span> <span class="o">=</span> <span class="s2">""</span> <span class="o">]</span>; <span class="k">then
</span><span class="nv">tmp</span><span class="o">=</span><span class="nv">$opt</span>
<span class="k">continue
elif</span> <span class="o">[</span> <span class="s2">"</span><span class="nv">$tmp</span><span class="s2">"</span> !<span class="o">=</span> <span class="s2">"</span><span class="nv">$opt</span><span class="s2">"</span> <span class="o">]</span>; <span class="k">then
</span>rickroll
<span class="k">fi
fi
done
for </span>var <span class="k">in</span> <span class="s2">"</span><span class="nv">$@</span><span class="s2">"</span>
<span class="k">do
if</span> <span class="o">[[</span> <span class="s2">"</span><span class="nv">$var</span><span class="s2">"</span> <span class="o">=</span> <span class="s2">"--force"</span> <span class="o">&amp;&amp;</span> <span class="s2">"</span><span class="nv">$tmp</span><span class="s2">"</span> <span class="o">=</span> <span class="s2">"r"</span> <span class="o">]]</span>; <span class="k">then
</span>rickroll
<span class="k">fi
done</span>
<span class="c"># If it's safe, just run rm</span>
/bin/rm <span class="s2">"</span><span class="nv">$@</span><span class="s2">"</span>
<span class="nb">exit</span> <span class="nv">$?</span></code></pre></figure>
<p>It may look messy to a UNIX guy more experienced than me, but it works. The <code class="highlighter-rouge">getopts</code> built-in sees if both the <code class="highlighter-rouge">-r</code> and the <code class="highlighter-rouge">-f</code> flags are used and, if so, it starts <code class="highlighter-rouge">rickroll()</code>, which opens with <code class="highlighter-rouge">xdg-open</code> that amazing clip from RickAstleyVEVO. From line 30 and below, the script checks if the <code class="highlighter-rouge">--force</code> flag is used instead of <code class="highlighter-rouge">-f</code>.</p>
<p>Give execute permissions to the script we’ve just created:</p>
<figure class="highlight"><pre><code class="language-bash" data-lang="bash"><span class="c"># chmod +x /bin/rmAlias</span></code></pre></figure>
<p>Restart your shell, and enjoy. If you want to test safely, I suggest trying to run <code class="highlighter-rouge">rm -rf</code> with no folders or one nonexistant, since this script stop even these commands.</p>
<p>If you want even more security, you can rename this script to <code class="highlighter-rouge">/bin/rm</code> and move the original one in some other place, getting rid of all the aliases. I prefer the solution above because it’s tidier: you haven’t to move anything. In fact, this could be just an AUR package…</p>
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