<!DOCTYPE html> <html class="no-js" lang="en-us" prefix="og: http://ogp.me/ns# fb: http://ogp.me/ns/fb#"> <head> <meta charset="utf-8"> <base href="https://beckmeyer.us/"> <meta name="viewport" content="width=device-width"> <title>Hello doas – Joel Beckmeyer's Blog</title> <link rel="stylesheet" href="/css/styles.css"> <link id="theme_css" rel="stylesheet" href="/css/themes/light.css"> </head> <body> <input class="show-hide-menu-input" style="display:none;" autocomplete="off" type="checkbox" id="toggle-1"> <div class="main"> <div class="header"> <div class="header-content"> <div class="title"> <a href="https://beckmeyer.us/">Joel Beckmeyer's Blog</a> </div> <div> <div class="header-right"> <label id="show-hide-menu-label" class="clickable-header-label" for="toggle-1"> <img class="color-adapting-image" width="30" src="/images/hamburger.svg" alt="menu button"> </label> </div> <label class="overlay" for="toggle-1"></label> <div class="dont-show"> Links: </div> <ul class="links"> <li><a href="/">Home</a></li> <li><a href="/contact/">Contact</a></li> <li><a href="/posts/">Posts</a></li> </ul> </div> </div> </div> <div class="body"> <div class="body-content"> <div class="title-header"> <h1>Hello doas</h1> <div class="title-header-date"> <time>Saturday, January 30, 2021</time> </div> </div> <p>Today, I switched my workstation from <code>sudo</code> to <code>doas</code>. I’m running Void Linux, and the process was fairly easy.</p> <p>First, I needed to figure out how to remove <code>sudo</code> (yes, I realize I could have installed <code>doas</code> first, then removed <code>sudo</code>, but I decided to do it the hard way.) As it turns out, the <a href="https://docs.voidlinux.org/xbps/advanced-usage.html#ignoring-packages">advanced usage section of the XBPS manual</a> details how to use the <code>ignorepkg</code> entry in xbps.d with nothing other than this exact use case! I created the file <code>/etc/xbps.d/20-ignorepkg-sudo.conf</code> with contents</p> <pre tabindex="0"><code>ignorepkg=sudo </code></pre><p>and then ran <code>sudo xbps-remove sudo</code> (an ironic command).</p> <p>After that, because I was stupid and removed <code>sudo</code> before I had set up <code>doas</code>, I had to use plain-old <code>su</code> to change to the root user and run <code>xi opendoas</code>. I also configured <code>doas</code> in <code>/etc/doas.conf</code> with the following:</p> <pre tabindex="0"><code># see doas.conf(5) for configuration details permit nopass keepenv :admin </code></pre><p>I ran <code>groupadd admin</code>, <code>usermod -aG admin joel</code>, and then logged out so that my user account would see the new group perms.</p> <p>And just like that, I can now run <code>doas xbps-install ...</code> and all of my other commands, just substituting <code>doas</code> for <code>sudo</code>.</p> <p>The one thing I immediately missed was <code>sudoedit</code>. Before I accidentally tried to use <code>sudo</code> for the first time, I had already accidentally tried to run <code>sudoedit</code> <em>at least</em> 5 times. I had to fix this. I saw a discussion on Reddit where <a href="https://www.reddit.com/r/linux/comments/l6y7nv/is_doas_a_good_alternative_to_sudo/gl4hs42?utm_source=share&utm_medium=web2x&context=3">one user suggested</a> writing a script to replace the <code>sudoedit</code> functionality. I quickly starting hacking together something like that. I started with:</p> <pre tabindex="0"><code>#!/bin/sh mkdir -p /tmp/doasedit doas cp $1 /tmp/doasedit/tmp_file $EDITOR /tmp/doasedit/tmp_file </code></pre><p>And quickly ran into my first road-block. The script is going to have to change the permissions of that file before the user can edit it. But if the script changes the permissions, how can I restore it to the original location with the right permissions? <code>cp /tmp/doasedit/tmp_file $1</code> won’t work. I thought about just using cat to overwrite the file contents in-place (<code>cat /tmp/doasedit/tmp_file > $1</code>). That <em>could</em> create some issues if a program has the file open. Instead, a better option is to create two copies of the file–one for editing, and one for preserving file attributes:</p> <pre tabindex="0"><code>#!/bin/sh mkdir -p /tmp/doasedit doas cp $1 /tmp/doasedit/edit doas chown -R $USER:$USER /tmp/doasedit/edit doas cp $1 /tmp/doasedit/file $EDITOR /tmp/doasedit/edit cat /tmp/doasedit/edit | doas tee /tmp/doasedit/file 1>/dev/null doas mv -f /tmp/doasedit/file $1 rm -rf /tmp/doasedit </code></pre><p>Of course, the issue with this is that it only works with absolute paths. I want to make it work for relative paths as well. I’m going to take advantage of <code>realpath</code>, which is part of the <code>coreutils</code> package from Void. As a bonus, this will also take care of the edge case where the given file is a symlink (IIRC, <code>sudoedit</code> didn’t follow symlinks, so I may be diverging here):</p> <pre tabindex="0"><code>#!/bin/sh mkdir -p /tmp/doasedit srcfile="$(realpath $1)" doas cp $srcfile /tmp/doasedit/edit doas chown -R $USER:$USER /tmp/doasedit/edit doas cp $srcfile /tmp/doasedit/file $EDITOR /tmp/doasedit/edit cat /tmp/doasedit/edit | doas tee /tmp/doasedit/file 1>/dev/null doas mv -f /tmp/doasedit/file $srcfile rm -rf /tmp/doasedit </code></pre><p>At this point, it works…okay-ish. It can only be used in one instance currently since I hard-coded <code>/tmp/doasedit/file</code> and <code>/tmp/doasedit/edit</code>, but that’s easily fixed:</p> <pre tabindex="0"><code>#!/bin/sh destfile_pfx="$(cat /dev/urandom | tr -cd 'a-f0-9' | head -c 32)" while [ -d "/tmp/doasedit/$destfile_pfx" ]; do destfile_pfx="$(cat /dev/urandom | tr -cd 'a-f0-9' | head -c 32)" done mkdir -p /tmp/doasedit/$destfile_pfx srcfile="$(realpath $1)" doas cp $srcfile /tmp/doasedit/$destfile_pfx/edit doas chown -R $USER:$USER /tmp/doasedit/$destfile_pfx/edit doas cp $srcfile /tmp/doasedit/$destfile_pfx/file $EDITOR /tmp/doasedit/$destfile_pfx/edit cat /tmp/doasedit/$destfile_pfx/edit | doas tee /tmp/doasedit/$destfile_pfx/file 1>/dev/null doas mv -f /tmp/doasedit/$destfile_pfx/file $srcfile rm -rf /tmp/doasedit/$destfile_pfx </code></pre><p>At this point, the only thing missing is the check to see if the file was actually edited:</p> <pre tabindex="0"><code>... cat /tmp/doasedit/$destfile_pfx/edit | doas tee /tmp/doasedit/$destfile_pfx/file 1>/dev/null if cmp -s "/tmp/doasedit/$destfile_pfx/file" "$srcfile"; then echo "Skipping write; no changes." else doas mv -f /tmp/doasedit/$destfile_pfx/file $srcfile fi ... </code></pre><p>I put this in a <a href="https://github.com/AluminumTank/doasedit">repo on GitHub</a> if anyone is interested. I know that a major weakness of this script is the number of times it calls <code>doas</code>, which could break flows where password is required every time <code>doas</code> is run.</p> </div> </div> </div> <hr class="dont-show"> <div class="footer"> <p>Have any questions? Let me know on <a href="https://matrix.to/#/@joel:thebeckmeyers.xyz">Matrix</a>, or start a discussion on <a href="https://social.beckmeyer.us/TinfoilSubmarine">Fediverse</a>!</p> </div> </body> </html>