Scheduling Time Machine backups from the command line

So I have an old Mac Mini which will just not start a backup to my time machine server. We could go over the reason but that is the subject for another article. The point is running it from the GUI does not work. However, I can go to the terminal window and do

raub@slowmac:~$ tmutil startbackup

all day and it works fine. In fact, I have been doing that manually to have a semblance of a backup:

dalek@strangepork:~$ tmutil latestbackup
/Volumes/Time Machine Backups/Backups.backupdb/strangepork/2018-07-16-234250
dalek@strangepork:~$ tmutil listbackups
[...]
/Volumes/Time Machine Backups/Backups.backupdb/strangepork/2018-05-01-130725
/Volumes/Time Machine Backups/Backups.backupdb/strangepork/2018-05-24-032218
/Volumes/Time Machine Backups/Backups.backupdb/strangepork/2018-06-21-001720
/Volumes/Time Machine Backups/Backups.backupdb/strangepork/2018-07-08-201058
/Volumes/Time Machine Backups/Backups.backupdb/strangepork/2018-07-16-234250
/Volumes/Time Machine Backups/Backups.backupdb/strangepork/2018-08-22-131023
dalek@strangepork:~$ 

But that is a bit of a drag. As you can see I am not manually doing it as often as I should. We need to automate this. Hmmm... recurring job... if this was Linux, Solaris, FreeBSD, or AIX, I would use a cronjob. But this is a Mac... running OSX. What should I do? Look for some App?

Wait a minute. OSX is UNIX with some sprinkles on the top. So, let's cron this out!

I am going to start the task off my normal account since I do not have to run startbackup from root. First let's see cronjobs I have right now:

dalek@strangepork:~$ crontab -l
#
dalek@strangepork:~$

Nothing at all, which is as good place to start as any. Now we need to add the entry. I like to specify the path of the program I am using in case there are old versions. So from

I will be using /usr/bin/tmutil. Now let's edit the crontab, which is done by typing crontab -e. That put me in a vim session (that can be configured); if you do not know it, it is a good time to learn. Here are a few quick pointers:

• When in doubt, press the escape key a lot.
• After you press esc a lot, if you want to save your changes and quit, type :wq, but if you do not want to save, type :q!

I do not know how often timemachine usually runs, so I will guess every two hours and will tell my cronjob to start at 15 minutes past the hour every 2 hours. In cron-lese, that looks like this

15  */2  * * *  /usr/bin/tmutil startbackup

After we save it, let's verify that our little work is committed:

dalek@strangepork:~$ crontab -l
#
15  */2  * * *  /usr/bin/tmutil startbackup
dalek@strangepork:~$

Then, give it a few hours and run tmutil listbackups to see if the backup cron jobs are being run every two hours.