I did a further check on the wiper script by changing the "percent_keep" from 85.0 to 75.0, and running the script in "dry_run" mode again. The script then output to console the names of all the files it would delete in order to free up the required amount of space (but didn't actually delete any files as it was a dry run). Seemed to be sensible.

To set up the cron job, I did the following on FB1:

• crontab -e opened up the crontab
• Copied over a script called "wiper.cron" from /opt/rtcds/caltech/c1/target/fb to /opt/rtcds/caltech/c1/target/daqd. This essentially contains a bunch of instructions to run the wiper script with the --delete flag, and write the console output to a log file.
• Added the following line: 33 3 * * * /opt/rtcds/caltech/c1/target/daqd/wiper.cron. So the cron job should be executed at 3:33AM everyday.
• The cron daemon seems to be running - sudo systemctl status cron.service yields the following output:
  controls@fb1:~ 0$ sudo systemctl status cron.service
● cron.service - Regular background program processing daemon
   Loaded: loaded (/lib/systemd/system/cron.service; enabled)
   Active: active (running) since Mon 2017-09-18 18:16:58 PDT; 27min ago
     Docs: man:cron(8)
 Main PID: 30183 (cron)
   CGroup: /system.slice/cron.service
           └─30183 /usr/sbin/cron -f
  Sep 18 18:16:58 fb1 cron[30183]: (CRON) INFO (Skipping @reboot jobs -- not system startup)
Sep 18 18:17:01 fb1 CRON[30205]: pam_unix(cron:session): session opened for user root by (uid=0)
Sep 18 18:17:01 fb1 CRON[30206]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Sep 18 18:17:01 fb1 CRON[30205]: pam_unix(cron:session): session closed for user root
Sep 18 18:25:01 fb1 CRON[30820]: pam_unix(cron:session): session opened for user root by (uid=0)
Sep 18 18:25:01 fb1 CRON[30821]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Sep 18 18:25:01 fb1 CRON[30820]: pam_unix(cron:session): session closed for user root
Sep 18 18:35:01 fb1 CRON[31515]: pam_unix(cron:session): session opened for user root by (uid=0)
Sep 18 18:35:01 fb1 CRON[31516]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Sep 18 18:35:01 fb1 CRON[31515]: pam_unix(cron:session): session closed for user root

   

• crontab -l on FB1 now shows the following:
  controls@fb1:~ 0$ crontab -l
# Edit this file to introduce tasks to be run by cron.
#
# Each task to run has to be defined through a single line
# indicating with different fields when the task will be run
# and what command to run for the task
#
# To define the time you can provide concrete values for
# minute (m), hour (h), day of month (dom), month (mon),
# and day of week (dow) or use '*' in these fields (for 'any').#
# Notice that tasks will be started based on the cron's system
# daemon's notion of time and timezones.
#
# Output of the crontab jobs (including errors) is sent through
# email to the user the crontab file belongs to (unless redirected).
#
# For example, you can run a backup of all your user accounts
# at 5 a.m every week with:
# 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/
#
# For more information see the manual pages of crontab(5) and cron(8)
#
# m h  dom mon dow   command
33 3 * * * /opt/rtcds/caltech/c1/target/daqd/wiper.cron

Let's see if this works.