[ID 10 T error SOLVED] root crontab deleted after reboot

[Daddyfix]

Hello All,

I have been racking my brain on a problem with my cron. Any insight will be appreciated

Senario Pi user
1. Create a cron entry with nano

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crontab -e

2. Get this Permission Error

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no crontab for pi - using an empty one
/tmp/crontab.B8LA9a: Permission denied
Creation of temporary crontab file failed - aborting

3. Directory permissions (there is so such file on my other RPi's)

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drwxr-xr-x 3 root     root 4.0K Oct 11 14:07 cron

and cron has crontabs with a sticky bit 'T'

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drwx-wx--T 2 root crontab 4.0K Oct 11 14:07 crontabs

also crontabs directory is empty

Senario root user
1. Create a cron entry with nano

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crontab -e

2. Get this General message

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# 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

3. Add a simple task to the end of the crontab file

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# HELLO WORLD
@reboot echo "Hello World" > /var/log/reboot.txt 2>&1

4. Save file and exit

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no crontab for root - using an empty one
crontab: installing new crontab

5. Returning to edit shows the file is intact
6. cat /var/spool/cron/crontabs/root shows the file is intact
7. Reboot RPi3
8. /var/spool/cron/crontabs/root IS GONE!. There is no cron file for root
9. list the root user crontab

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crontab -l
no crontab for root

Problem
cron file for root (/var/spool/cron/crontabs/root) gets deleted sometime before or after rebooting

Searching for Solutions
There is nothing in /var/log/ when I

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cat /var/log/syslog | grep cron
cat /var/log/boot.log | grep cron

It clearly gets deleted after rebooting... but why? How do I get more informatio here?
systemctl status cron.service

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● cron.service - Regular background program processing daemon
   Loaded: loaded (/lib/systemd/system/cron.service; enabled)
   Active: active (running) since Tue 2016-10-11 14:49:44 EDT; 3min 21s ago
     Docs: man:cron(8)
 Main PID: 322 (cron)
   CGroup: /system.slice/cron.service
           └─322 /usr/sbin/cron -f

Oct 11 14:49:44  systemd[1]: Starting Regular background program processing daemon...
Oct 11 14:49:44  systemd[1]: Started Regular background program processing daemon.
Oct 11 14:49:44  cron[322]: (CRON) INFO (pidfile fd = 3)
Oct 11 14:49:44  cron[322]: /var/spool/cron: No such file or directory
Oct 11 14:49:44  cron[322]: /var/spool/cron: created
Oct 11 14:49:44  cron[322]: crontabs: No such file or directory
Oct 11 14:49:44  cron[322]: crontabs: created
Oct 11 14:49:44  cron[322]: crontabs: chowned
Oct 11 14:49:44  cron[322]: (CRON) INFO (Running @reboot jobs)

cat /etc/default/cron

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# Cron configuration options

# Whether to read the system's default environment files (if present)
# If set to "yes", cron will set a proper mail charset from the
# locale information. If set to something other than 'yes', the default
# charset 'C' (canonical name: ANSI_X3.4-1968) will be used.
#
# This has no effect on tasks running under cron; their environment can
# only be changed via PAM or from within the crontab; see crontab(5).
READ_ENV="yes"

# Extra options for cron, see cron(8)
#
# For example, to enable LSB name support in /etc/cron.d/, use
# EXTRA_OPTS='-l'  
#
# Or, to log standard messages, plus jobs with exit status != 0:
# EXTRA_OPTS='-L 5'
#
# For quick reference, the currently available log levels are:
#   0   no logging (errors are logged regardless)
#   1   log start of jobs
#   2   log end of jobs
#   4   log jobs with exit status != 0
#   8   log the process identifier of child process (in all logs)
#
#EXTRA_OPTS=""

What I tried
1. Tried uninstalling and reinstalling (not fixed)

Possible solution
1. Edit the /etc/crontab. It doesn't seem to get deleted

Please help.

[Daddyfix]

ARGGGGGGG!

SOLVED
In my attempt to make the RPI3 more robust. I had set the rootfs to boot from USB.
In that process I had set the /var/spool as a symbolic link that pointed to /tmp, which is a tmpfs in memory

Its an ID 10 T Error!