How to setup and debug a cronjob in macOS

I was surprised to see that macOS comes with cron pre-installed. A cron job is basically a recurring scheduled task, e.g. a script or command that is run every Tuesday on 2pm. To check if there any existing cron jobs run:

$ crontab -l
crontab: no crontab for alinz - using an empty one
crontab: no changes made to crontab

Let's say I want to commit my Obsidian notes once a day. First I write a small script that contains the commit logic before I setup the cron job.

$ cat <<"EOD">~/.local/bin/ && chmod +x ~/.local/bin/
#!/usr/bin/env bash

set -eu

pushd ~/Documents/Obsidian
git add --all
git commit -m "Obsidian notes from $(date -Idate)"

Note that the script above contains quite a bit of bash magic. It's perfectly fine to write the script file and set the executable flag in two separate commands. Also, if you quote the delimiter in a HEREDOC statement, like "EOD" in the example above, then no evaluation happens in the content. Otherwise the $(date -Idate) would've been evaluated to 2023-04-23 in the script.

Since we have the script our only remaining step is to setup the cron job. Cron's syntax is a bit intricate and I'd recommend to use an online tool like to define the desired cron schedule expression. Running the job every day at 8pm can be expressed as 0 20 * * *.

To define the job run crontab -e and enter 0 20 * * * ~/.local/bin/ But there's something missing which will make the cron job fail. Cron job errors will be reported to your local mail account, yes there's a local mail account for your user account. To read those mail just run mail in a terminal. You'll see the following error:

~/Documents/Obsidian ~
fatal: Unable to read current working directory: Operation not permitted

We need to give /usr/sbin/cron full disk access in order to fix the issue. Please let me know if there's a way to restrict access of cron just to a particular directory. Open system, then Privacy & Security and under Full Disk Access click the + button at the bottom to add /usr/sbin/cron. Note that you can use Cmd+Shift+G to enter a particular location in the file select dialog (this also works in Finder).

Et voila, you now know how to setup and debug a cron job on macOS.

PS: If your git is configured to automatically sign a commit add --no-gpg-sign to the git commit call or otherwise the cron job will fail because it cannot unlock your signing key.