Linux – How to get a cron job to run every 30 minutes

You would have to run this as root, but:

for user in $(cut -f1 -d: /etc/passwd); do crontab -u $user -l; done

will loop over each user name listing out their crontab. The crontabs are owned by the respective users so you won't be able to see another user's crontab w/o being them or root.

Edit if you want to know which user a crontab belongs to, use echo $user

for user in $(cut -f1 -d: /etc/passwd); do echo $user; crontab -u $user -l; done

ok well here's a solution:

    <key>StartCalendarInterval</key>
<array>
    <dict>
        <key>Minute</key>
        <integer>0</integer>
    </dict>
    <dict>
        <key>Minute</key>
        <integer>55</integer>
    </dict>
</array>

So it seems you need to set up a dict for each repeated job.