Check journalctl -fa and if it shows something like below over and over again:

The following packages have unmet dependencies:
 docker-ce : Depends: libseccomp2 (>= 2.3.0) but 2.2.3-3ubuntu3 is to be installed
E: Unable to correct problems, you have held broken packages.

To fix:

apt update

You might have to run the above command a couple of times since it might says it cannot get the lock. Once the update is done, it should update automatically.

This dosen't Works for me.
i can't update from 2.0.1 to 2.1.0

the update process remains at "Downloading and installing new version"
i am using Ubuntu Server 16.04.3 LTS

Please Help

First check if sudo du -hcs /var/tmp has lots of data. Or check if /boot is full using df -h /boot. If /boot is full, you have to manually remove some of the old kernels:

root@my:/boot# uname -nar
Linux my.cloudron 4.4.0-112-generic #135-Ubuntu SMP Fri Jan 19 11:48:36 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
root@my:/boot# rm initrd.img-4.4.0-101-generic initrd.img-4.4.0-103-generic

Now /boot should have some free space:

apt -f install
purge-old-kernels   # this removes old kernels and cleans up /boot
rm -rf /var/tmp/mkinitramfs*
dpkg --configure -a
apt-get install
apt autoremove

Check if unbound is working:

systemctl status unbound

It must say active (running). If not, run the following commands:

sudo unbound-anchor -a /var/lib/unbound/root.key
sudo systemctl restart unbound

• (only multi-domain email setups) If there was an alias in one domain with name say 'foobar' and a mailbox in another domain with the same name 'foobar', then the migration code sometimes imports the mailbox of the second domain incorrectly as an 'alias' instead of a 'mailbox'. If you encounter this issue, please contact us at support@cloudron.io (and enable ssh access). We have to patch up the DB by hand. Note that the mail server itself is running fine and there is no issue sending/receiving email. Just that the db entry is wrong which causes authentication to fail.