Add new guide, and 2024 guide section
Nathan Steel
1 year ago
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="utf-8">
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<meta name="viewport" content="width=device-width, initial-scale=1">
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<meta name="description" content="A guide to adding a free SSL certificate to your website(s) using cerbot, and automatically renewing them">
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<meta name="keywords" content="Blog, articles, guide, certbot, SSL, secure certificate, website">
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<meta name="author" content="Nathan (Aney) Steel">
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<meta name="theme-color" content="white">
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<meta name="theme-color" content="black">
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<link rel="stylesheet" type="text/css" href="/main.css">
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<link rel="icon" type="image/png" href="/images/favicon.svg">
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<title>Linux File Permissions</title>
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</head>
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<body>
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<header>
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<a href="#main" class="vh">Jump directly to main content</a>
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<h1>Linux File Permissions</h1>
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<input id="burger-toggle" type="checkbox"/>
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<label class="burger-container" for="burger-toggle"><div class="burger"></div><span class="sr">Burger menu</span></label>
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<hr/>
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<nav>
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<a href="/">home</a>
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<a href="/about.html">about</a>
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<a href="/projects.html">projects</a>
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<a href="/blog/">blog</a>
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<a href="/sitemap.html">misc</a>
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<a href="/support.html">support</a>
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</nav>
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<hr/>
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</header>
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<main id="main">
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<section>
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<p>Having multiple users and groups with access to the same linux PC/server is great, but not everyone should have access to everything, eh.</p>
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<p>For this, we'll use an example file, and switch ownership between root, and our user. So run the following snippet if your're using this as a tutorial, otherwise just read on.</p>
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<pre><code>mkdir ~/permsExample && cd ~/permsExample && sudo touch FILENAME</code></pre>
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<h2>Basic File Permisssion Breakdown</h2>
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<p>For certain things, such as computers with only a few users/groups this works splendid.</p>
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<p>If we run a <code>ls -l FILENAME</code>, we'll see something along the lines of the below.</p>
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<pre><code>-rw-r--r-- 1 root root 0 Sep 14 13:02 FILENAME</code></pre>
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<p><code>-rw-r--r--</code> being the permissions for User, Group, and Others which can be rwx for read, write, and executable permissions. Set in groups of 3s for User/Group/Others respectively.</p>
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<p><code>root root</code> refers to the owner user and owner group.</p>
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<h2>Set User/Group Ownership</h2>
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<p>Each file, and directory within UNIX has an owner user, and owner group.<br>
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By default when you create a file your user will be the owner, and your usergroup will be the owner group.</p>
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<p>This can be changed with a simple command (that may need to be run with sudo).</p>
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<pre><code>chown USER FILENAME
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chown :GROUP FILENAME
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chown USER:GROUP FILENAME</code></pre>
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<p>The above snippet has the <code>chown</code> command run three different times with different purposes.
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The first is to change just the owner user, second to change just the owner group,
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and third to change both at the same time.</p>
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<p>So to change the owner user for FILENAME to our own user, we'd run <code>sudo chown $USER FILENAME</code>, then verify the change by running <code>ls -l FILENAME</code>.</code></p>
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<h2>Set Permissions for User/Group/Others</h2>
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<p>Now we'll take a look at the file permissions that will affect the owners, and all other users.</p>
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<p>If we look back at the <code>ls -l FILENAME</code> mentioned earlier you'll recall the brief <code>-rw-r--r--</code> mention.</p>
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<h3>Intro to the rw-r--r-- meaning</h3>
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<p>There are 10 dashes (-) that can be set, ignoring the first for now leaves us with 9, seperated by 3s.</p>
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<p>The first group of three <code>rw-</code> in this example shows that the owner user has read/write permissons, but no executable permissions.
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<br>The second group <code>r--</code>, shows the owner group only has read permissions, not write/executable permissions.
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<br>And the third group <code>r--</code>, shows that other users have read permissions, but cannot write/execute the files.</p>
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<h3>Set permissions</h3>
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<p>The below commands will set read, write, and execute permissions for the user, and group and give all other users read permissions for filename.file.</p>
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<pre><code>chmod ug+rwx FILENAME
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chmod o+r FILENAME</code></pre>
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<p>First thing after the <code>chmod</code> command (and a space) can be any combination of <code>ugoa</code>. Referring to user, group, other, and all.</p>
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<p>Second, immediately after the letters can be one of <code>+,-,=</code> which are used to add, remove, or set (exact) permissions.</p>
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<p>Third, any combination of <code>rwx</code> for read, write, executable permissions.</p>
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<p>Follow this up with a space and the file/directory name and poof, permissions are set. If you'd like to set permissions for all files within a directory (and not just new ones created), also add a <code> -R</code> at the end of the command.</code></p>
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<h4>Set permissions by number</h4>
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<p>Many guides, examples, snippets, and such do not give their demonstration of setting permissions in the same manner as above, instead they'll use numbers, such as the below.</p>
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<pre><code>chmod 755 FILENAME</code></pre>
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<p>This chmod command will give rwx permissions to the owner user, and rx to the owner group, and other.</p>
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<p>The numbers are much simpler to understand than you'd think:
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<br>4 = Read
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<br>2 = Write
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<br>1 = Execute/executable
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</p>
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<p>These numbers get added up and grant those permissions to the users. So 7 = rwx, 6 = rw, 5 = rx, 3 = wx, 0 = no permissions, etc.</p>
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<p>You'll also spot that there are 3 numbers, 7,5,5. These are for user, group, and other respectively. So each rwx number up to 7 sets the permissions for different users.</p>
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<h3>Chmod directories</h3>
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<p>The <code>chmod</code> command can also be used on directories. The following example will give all permissions to all users for that directory, and all its child files/directories.</p>
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<pre><code>chmod a=rwx directoryName -R</code></pre>
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</section>
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</main>
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<footer>
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<hr/>
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<p>Written by <a href="https://aney.co.uk" target="_blank" rel="noopener">@aney</a> with <a href="https://danluu.com/web-bloat/" target="_blank" rel="noopener">web bloat</a> in mind | <a href="https://github.com/Aney/website" target="_blank" rel="noopener">Source Code</a></p>
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</footer>
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</body>
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</html>
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