Yes. BUT there are a couple of tasks active on our systems and those will stop too.
Is cron a necessary service for a ubuntu desktop or can I completely remove this from my system?
I would suggest it is necessary but as always with Linux ... your choice to decide :) Might I suggest another method: why not flag changes to /etc/cron*/, /etc/crontab and /var/spool/cron/crontabs//? That might be a lot less trouble as you get to keep the normal cron jobs active. Just need to create a watchdog and set it loose on those directories.
A run down on cron from my system (yours might have more, the same or less actions) ...
$ ls /etc/cron.daily/
0anacron cracklib-runtime man-db samba
apport dpkg mlocate update-notifier-common
apt-compat google-chrome passwd
bsdmainutils logrotate popularity-contest
$ ls /etc/cron.weekly/
0anacron man-db update-notifier-common
$ ls /etc/cron.monthly/
So generally I would investigate any of these (like popularity-contest is all fine and dandy but I could live without it). mlocate might be an issue: that one updates the locate command so could be useful. And so on. EACH of these you could run manually.
Each of the files will have an explanation:
rinzwind@schijfwereld:~$ more /etc/cron.monthly/0anacron
# anacron's cron script
# This script updates anacron time stamps. It is called through run-parts
# either by anacron itself or by cron.
# The script is called "0anacron" to assure that it will be executed
# _before_ all other scripts.
test -x /usr/sbin/anacron || exit 0
anacron -u cron.monthly
anacron has its own service:
$ systemctl list-unit-files | grep cron
Now for the command (stop and start):
sudo systemctl stop crond.service
sudo systemctl start crond.service
sudo systemctl stop anacron.service
sudo systemctl start anacron.service
sudo systemctl stop anacron.timer
sudo systemctl start anacron.timer
(I did not test each of them ;) )
Plus there is more than that: a user cron is also active; you can disable those with ...
sudo touch /var/spool/cron/crontabs/$USER
sudo chmod 0 /var/spool/cron/crontabs/$USER
for every user on your system (make copies of the files please so you can restore them if you want to restore them) (oddly I have not found a systemd service for user crons and I doubt it is dealt with from cron.service).