[Technology] systemd timers and service files in place of cron

I keep a daily journal in an Emacs org-mode file.  Sometimes due to clumsy keypresses in Emacs, I have temporarily deleted (!) lines or sections (!).  I think I have always caught these mistakes, but to be safe, I decided to create a git repository for it and do a daily commit.

In the past, I'd have used a cron job, but in recent years I've tried to make more and more use of systemd and timers.  Is one better than the other?  I'm going to ignore that question and proceed. :D

For this task, which I'm calling "log_git_committer" (very uninspired), I have four files:

• log_git_committer.sh - a Bash script that handles actually committing changes
• log_git_committer.service - a systemd service file that references the .sh file
• log_git_committer.timer - a systemd timer file that implicitly references .service unit and describes the interval
• Makefile - a simple make file to install and uninstall my files as I work on it

Below are some of the more interesting notes from working on it, and the systemd files. 

Notes

Some notable pieces that came up:

• .service:
  
• Type=oneshot: since I'm running this from a timer, I just want this service unit to be a "oneshot", as it's not actually a service that would keep running in the background.
  
• ExecStart= and %h: I'm installing the shell script locall in my ~/.local/bin directory.  ExecStart in a .service won't accept ~/ or $HOME/ in a path, preferring absolute paths.  However, systemd has some specifiers like %h that will substitute in a user's path when a service unit is run with --user. 
• .timer:
• OnCalendar=: it has a lot of options that are similar to cron.  Neat. 
• retroactively running missed timers?  Yes, if I set a timer to run at 3AM but I put my computer to sleep at 1AM and turn it back on at 8AM, the timer will then execute.  If I end up in Narnia and my computer is asleep for 3 days while I'm away (a lifetime there), it will then run the service just once to catch up.  Nice.
  
• Makefile:
  
• unit file syntax checking: systemd provides a command that lets you analyze your unit files to check for correctness. E.g.
  
  systemd-analyze verify log_git_committer.timer
  systemd-analyze verify log_git_committer.service
  
  so I added that to a target.
  
• systemd install directory: for non-root user services and timers, the install directory is ~/.config/systemd/user/
  Some other locations on my Fedora 38 system for systemd unit files include:
• /usr/lib/systemd/user/
• /usr/lib/systemd/service/
• /etc/systemd/user/
• /etc/systemd/system/
  
• systemd and reloading updated .service files: if I make a change to a .service file, systemd would like me to reload the new one from disk.  So, in my Makefile, after I copy .service and .timer files into their install directory, I call:
  
  systemctl --user daemon-reload

log_git_committer.sh

If there's interest, I can share this, but it's pretty simple and straight forward.

log_git_committer.service

[Unit]
Description=Commit changes to a log file

[Service]
Type=oneshot
ExecStart=%h/.local/bin/log_git_committer.sh

[Install]
WantedBy=multi-user.target

 log_git_committer.timer

[Unit]
Description=Do a daily commit of the log file.

[Timer]
OnCalendar=3:00:00
Persistent=true

[Install]
WantedBy=timers.target

 Resources

• https://www.freedesktop.org/software/systemd/man/systemd.service.html
• https://wiki.archlinux.org/title/systemd
• https://wiki.archlinux.org/title/systemd/Timers
• https://wiki.archlinux.org/title/Systemd/User#Basic_setup
• https://documentation.suse.com/smart/systems-management/html/systemd-working-with-timers/index.html

 

[Technology] web development: TypeScript!

I used to be a snob about various technologies.  Two decades ago, I hated doing web development with JavaScript, dealing with browser quirks and what felt like deficiencies in the base standard and browser client libraries.  It felt like you couldn't write simple, safe and predictable code, especially without relying on a third party framework or library.

However, much has changed and I genuinely enjoy it now.  I still often prefer to write code without third-party libraries or frameworks if I can afford to, but I have increasingly come to rely on TypeScript.  I value type checking a lot, especially as projects grow and APIs evolve.  Managing types explicitly entails more work earlier on, but it also helps spare me from silly bugs and saves me time during refactoring or when revisiting code I wrote a while ago.  

TypeScript works by transcompiling TypeScript (in .ts files) into pure JavaScript.  Some of my favourite features include:

• getting to set language standard targets in configuration.  E.g. setting your target to "es2016" will mean the generated JavaScript will down-compile newer syntax into syntax that exists in ECMAScript 2016.  (Note: this doesn't polyfill API functionality!)
• easily defining interface types for simple objects with fixed property names
  

There's some effort to promote a native static type system in future ECMAScript, like this proposal: https://github.com/tc39/proposal-type-annotations.  I hope for this friendlier future.

[Technology] firejail: sandboxing with Linux namespaces

I am generally fairly wary of the amount of access software has on my computer.  Consequently, I like to use firejail on Linux to sandbox a lot of applications.  E.g. am I playing a single-player game from itch.io?  It doesn't need access to my mount points, my home directory (beyond the game's own directory for the program, game files and save data) or to the network.  Sometimes I am stunned by how much trust I put into random software back in 1998

It uses Linux namespace and seccomp-bfp.

An example command of what I might use would be:

$ firejail --net=none --disable-mnt --whitelist=/home/myuser/files/games/game_title/ ./game.sh

Some common programs have pre-existing profiles defined by firejail, like firefox, and those can be found in /etc/firejail.  In the case of firefox, one notable change is access to your home directory: it gets restricted to just your downloads folder!

[Technology] Blogger template: add back the edit button

Like poor Blogger user User 7100044714607836407, I have missed the quick edit button on newer Blogger templates. So I wrote a little snippet of JavaScript to bring it back.

Differences:

• Appears in the title instead of at the bottom.
• Does not appear until you press ctrl-e.
• In theory will show even when readers press ctrl-e, but of course they would still need to log in as you to actually get to the edit page.
• Just uses the blog and post IDs already viewable on the page.

Code

  window.addEventListener ("keydown", function (ev) {
    if (ev.code == "KeyE" && ev.ctrlKey == true) {
      let posts = document.querySelectorAll ("DIV.post-outer:not(.edit_link_added)") ?? [];
      for (let post of posts) {
        const blog_id = post.querySelector("meta[itemprop='blogId']").getAttribute ("content");
        const post_id = post.querySelector("meta[itemprop='postId']").getAttribute ("content");
        const post_title_h3 = post.querySelector (".post-title");

        let edit_a = document.createElement ("A");
        edit_a.href = `https://www.blogger.com/post-edit.g?blogID=${blog_id}&postID=${post_id}&from=pencil`;
        edit_a.target = "_blank";
        edit_a.innerText = "[✏]";
        post_title_h3.appendChild (edit_a);

        post.classList.add ("edit_link_added");
      }
    }
  });

[Technology] Memento: estate possession distribution

gitlab.com/aquarichy/kosmomemento

A while ago, I lost a dear family member.  It was a very challenging time, and a very important and heavy activity was helping box up their life, room by room.  There were a lot of memories tied to the physical possessions, and it was hard to make decisions for them at the time, so off they went to storage.

It's been long enough that the beneficiaries need to make collective decisions as to the disposal and distribution of the possessions (storage isn't cheap!)   So, as a fun personal project and an exercise in simple web development, I wrote Memento, which generates tables from a catalogue of photos to allow a group of people to vote on actions for each item.  

 As an example, imagine the beneficiaries are the characters from Scott Pilgrim vs. the World and the possessions are heirloom doughnuts that had been scattered across a couple cities (rather than rooms):

 

If you find this and find it useful, or are interesting in using it and need some help setting it up, let me know.