Can I use cron or launchd to run a bash script without being logged in?

Question

I'd like to have a simple bash script run (regardless of whether anyone is logged in or not) akin to putting it in /etc/cron.daily/ on Linux, but on Mac OS X Mountain Lion 10.8.4. If it's possible, how? All it needs to do is copy (and maybe bzip) a file.

Answer 1

Cron is officially deprecated, so you should use launchd.

There is a tutorial at apple: https://developer.apple.com/library/content/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/CreatingLaunchdJobs.html

A good starting point for explaining where to put the plist file

https://alvinalexander.com/mac-os-x/mac-osx-startup-crontab-launchd-jobs

A bit more details can be found at

http://www.launchd.info

Two things that got/confused me:

1) Pay attention between the difference between Program and ProgramArgments

2) If the job you want to run is a script, it needs to have the #!/bin/sh, otherwise launchd cannot start it, and you will end up with a confusing exit/status-code 78.

Answer 2

Using cron, you can edit the superuser's crontab with for example EDITOR=nano sudo crontab -e. When I tried adding a line like * * * * * say aa, the say command was run even after I logged out to the login window.

Using launchd, save a property list like this as for example /Library/LaunchAgents/test.plist:

<?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>test</string>
  <key>ProgramArguments</key>
  <array>
    <string>say</string>
    <string>bb</string>
  </array>
  <key>StartInterval</key>
  <integer>10</integer>
</dict>
</plist>

Then run sudo chown root /Library/LaunchAgents/test.plist and sudo launchctl load /Library/LaunchAgents/test.plist. The say command scheduled by launchd was also run when I logged out to the login window.