Please note that using
/etc/fstab is still the preferred approach with systemd!
See the man page for systemd.mount which states:
In general, configuring mount points through /etc/fstab is the preferred approach.
systemd ships systemd-fstab-generator which converts those to mount units.
If you really want to turn that mount into a mount unit, my recommendation is to check its current exact configuration, with the following command:
$ systemctl cat tmp.mount
$ systemctl cat /tmp
Which will show you the dynamic unit created by systemd-fstab-generator, and should look similar to:
# Automatically generated by systemd-fstab-generator
You could save these contents into
/etc/systemd/system/tmp.mount and run
systemctl enable tmp.mount to activate it. (You will need to add an
[Install] section and a
WantedBy=local-fs.target to be able to successfully enable it.)
(Another option is to use the tmp.mount from the systemd sources. Some other distributions, like Fedora, are shipping and enabling that one.)
Don't forget to remove the one from
/etc/fstab, otherwise they might conflict. (I believe the one in fstab would prevail, as I'd expect
/run to have priority over
But, as said before, managing through
/etc/fstab is still the preferred solution... So I'd probably recommend you still stick with that one.