Cron under MacOS

22 July 2020

I’m using plain text to store my information. This plain text is inside a git repo. To back it up I need to commit changes & push them to the remote. I was doing that manually. Yet this is not effective. I decided to use cron for that. Every 30min I want to execute a script that backs up my wiki. How to do that under mac?

Cron under MacOS

You cannot use cron. Instead Apple encourage to use launchctl. How to set up launchctl? At first you need to create plist file:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>com.krzysztofzuraw.wikibackup</string>

  <key>ProgramArguments</key>
  <array>
    <string>/Users/kzuraw/wiki/backup.sh</string>  <!-- script location -->
  </array>

  <key>Nice</key>
  <integer>1</integer>

  <key>StartInterval</key>
  <integer>1800</integer> <!-- 30min -->

  <key>RunAtLoad</key>
  <true/>

  <key>StandardErrorPath</key>
  <string>/tmp/wikibackup.err</string>

  <key>StandardOutPath</key>
  <string>/tmp/wikibackup.out</string>
</dict>
</plist>

Maybe you wonder what is nice key? After a bit of searching, I found out that it is used for scheduling priority. You can read more about it on man page of nice.

Going back to configuration. For launchctl to pick up your configuration plist file has to be placed under ~/Library/LaunchAgents. I prefer to use already existing plist naming convention: com.YOURNAME.CONFIGURATION_NAME.plist I named my plist as com.krzysztofzuraw.wikibackup.plist. If you have this setup execute launchctl load com.krzysztofzuraw.wikibackup.plist. Similarly if you need to unload it you can use launchctl unload com.krzysztofzuraw.wikibackup.plist. To see which launchctl scripts are running try launchctl list.

My lanuchctl script is running but how does backup.sh looks like?

#!/bin/zsh
cd ~/wiki # script still needs to enter folder even if backup script is inside the wiki
git add .
git commit -a -m "updated on `date +'%Y%m%d%H%M'`"
git push origin master

Summary

If you see to set up cron jobs under MacOS - use launchctl. You can read more at Mac crontab: Creating MacOS startup jobs with crontab, er, launchd. Original idea from Using VimWiki.