none, I've disabled cron messages in syslog.
*.*;cron,auth,authpriv.none -/var/log/syslog
All I have is the mail, send by the system (cron job with cat /var/log/pihole_updateGravity.log)
As I initially mentioned, I duplicated the cron job (changed the time) and had cron execute it again, same error message. I did (just now) this again, adding the line
echo "$PATH"
output (in the log file):
/usr/bin:/bin:/usr/local/bin/
which confirms my assumption the script (when executed with cron) doesn't know where to find service (/usr/sbin)
when running pihole -g from the command line, it does know this:
echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/local/games:/usr/games