Lots of Emails about failures when using cron to schedule a large batch job

I am using the cron functionality to run a backup of 5 of my virtual machines to another local disk. This is done using the backup command’s documented ability to take in more than one VM at a time.

The issue I’m having is, doing it this way, every minute I got an email with the lines:

2018-12-09 18:09:01.736433 INFO PROGRAM_VERSION Vertical Backup 1.2.2

2018-12-09 18:09:02.240558 INFO LICENSE_INFO Trial license expires on 2018-12-29

2018-12-09 18:09:02.243212 ERROR BACKUP_BUSY Another backup job is in progress

I get dozens of these 3 line emails. I’d rather not parallelize the jobs because I’d like one job to finish before the next one starts. Is there a way to get this not to send me 40+ emails but still have serial jobs?

Can you post here the relevant line in /var/spool/cron/crontabs/root?

Sure thing!

* */6 * * * /vmfs/volumes/5bfaecf1-b15c32a8-fa58-d4ae52863fb1/verticalbackup/vertical backup "HTTP Server" "EM - Win2012 AD" "Mail" "Minecraft" "Legacy Mail" --email --subject "Backup Job Completed"

To mitigate it for now, I swapped over to a shell script that executes each VM backup individually. This gets me the serial nature I’m looking for (my backup destination disk is a single large SATA drive, so it gets overwhelmed easily for I/O from the VMs which are hosted off SSDs), but I feel like the vertical backup command shouldn’t try to run all 5 at once.

Does backing up all vms take more than 6 hours? I wonder why you could get those emails every minute.