Ubuntu – Ubuntu 16.04 Core OS snap won’t remove

The snap command is actually made up of two components, server and client. You're interacting with the client. When you cancelled the install operation on the client side that's the only place you cancelled it-- the client. So it stopped showing you that it was installing, but it was still installing (this is a bug). (Update: This bug was fixed in snapd v2.20.1.)

On the server side, all of this stuff is happening in "changes." You can read more about them here, but for your purposes, you want to just abort this specific change. To do that, run:

$ snap changes
<snip>
203  Doing   2016-06-24T12:17:45Z  -  Install "nextcloud" snap

Note the ID, 203, and the fact that it's "Doing" it right now. To abort that operation, you use the change ID:

$ sudo snap abort 203

And the change should stop. However, I must say that the fact that the change froze partway through does not bode well for your ability to abort it. If it doesn't work, perhaps try rebooting. If that still doesn't seem to have fixed it and you're okay losing all your snaps and their data, you can completely reset the snapd state with this script.

resolved the issue at my own.

removed all the existing packages, with this below Note: before doing this, please to close all the tabs and other sheets as we do not know which process is hurdling the resolution.

1st: sudo apt autoremove

then, sudo apt-get clean then, sudo apt-get -f install then, sudo apt-get update then, sudo apt-get upgrade

And you are done with the fix.