Gfilui

After installing Ubuntu 18.04 I noticed high bandwidth traffic with the process snapd and since I don't use snap apps I decided to remove snap.

I used this command
$ sudo apt purge snapd ubuntu-core-launcher squashfs-tools

and this is the output

Reading package lists... Done
Building dependency tree 
Reading state information... Done
Package 'ubuntu-core-launcher' is not installed, so not removed
The following packages will be REMOVED:
 gnome-software-plugin-snap* snapd* squashfs-tools*
0 upgraded, 0 newly installed, 3 to remove and 0 not upgraded.
After this operation, 57.4 MB disk space will be freed.
Do you want to continue? [Y/n] 
(Reading database ... 317306 files and directories currently installed.)
Removing gnome-software-plugin-snap (3.28.1-0ubuntu4) ...
Removing snapd (2.32.5+18.04) ...
Removing squashfs-tools (1:4.3-6) ...
Processing triggers for man-db (2.8.3-2) ...
(Reading database ... 317244 files and directories currently installed.)
Purging configuration files for snapd (2.32.5+18.04) ...
Stopping snap-communitheme-97.mount
Stopping unit snap-communitheme-97.mount
Waiting until unit snap-communitheme-97.mount is stopped [attempt 1]
snap-communitheme-97.mount is stopped.
Removing snap communitheme and revision 97
Removing snap-communitheme-97.mount
Stopping snap-core-4486.mount
Stopping unit snap-core-4486.mount
Waiting until unit snap-core-4486.mount is stopped [attempt 1]
snap-core-4486.mount is stopped.
Removing snap core and revision 4486
Removing snap-core-4486.mount
Stopping snap-gnomex2d3x2d26x2d1604-59.mount
Stopping unit snap-gnomex2d3x2d26x2d1604-59.mount
Waiting until unit snap-gnomex2d3x2d26x2d1604-59.mount is stopped [attempt 1]
snap-gnomex2d3x2d26x2d1604-59.mount is stopped.
Removing snap gnome-3-26-1604 and revision 59
Removing snap-gnomex2d3x2d26x2d1604-59.mount
Stopping snap-gnomex2dcalculator-154.mount
Stopping unit snap-gnomex2dcalculator-154.mount
Waiting until unit snap-gnomex2dcalculator-154.mount is stopped [attempt 1]
snap-gnomex2dcalculator-154.mount is stopped.
Removing snap gnome-calculator and revision 154
Removing snap-gnomex2dcalculator-154.mount
Stopping snap-gnomex2dcharacters-69.mount
Stopping unit snap-gnomex2dcharacters-69.mount
Waiting until unit snap-gnomex2dcharacters-69.mount is stopped [attempt 1]
snap-gnomex2dcharacters-69.mount is stopped.
Removing snap gnome-characters and revision 69
Removing snap-gnomex2dcharacters-69.mount
Stopping snap-gnomex2dlogs-25.mount
Stopping unit snap-gnomex2dlogs-25.mount
Waiting until unit snap-gnomex2dlogs-25.mount is stopped [attempt 1]
snap-gnomex2dlogs-25.mount is stopped.
Removing snap gnome-logs and revision 25
Removing snap-gnomex2dlogs-25.mount
Stopping snap-gnomex2dsystemx2dmonitor-36.mount
Stopping unit snap-gnomex2dsystemx2dmonitor-36.mount
Waiting until unit snap-gnomex2dsystemx2dmonitor-36.mount is stopped [attempt 1]
snap-gnomex2dsystemx2dmonitor-36.mount is stopped.
Removing snap gnome-system-monitor and revision 36
Removing snap-gnomex2dsystemx2dmonitor-36.mount
Stopping snap-spotify-x1.mount
Stopping unit snap-spotify-x1.mount
Waiting until unit snap-spotify-x1.mount is stopped [attempt 1]
snap-spotify-x1.mount is stopped.
Removing snap spotify and revision x1
Removing snap-spotify-x1.mount
Final directory cleanup
Discarding preserved snap namespaces
umount: /run/snapd/ns/vlc.mnt: not mounted.
Removing extra snap-confine apparmor rules
Removing snapd cache
Removing snapd state

I noticed that it removed core system apps. How can I undo the process again to restore snap and those apps again.

thanks in advance

If you erroneously uninstall core packages on an Ubuntu system it's possible to put the deb packages back simply with one command:-

Note: This presumes you previously installed the stock Ubuntu product, and not one of the other flavours.

sudo apt install ubuntu-desktop^ 

Once snapd is re-installed (which it should be with the above command), you can re-install the snaps which come pre-installed with:-

sudo snap install gnome-calculator
sudo snap install gnome-characters
sudo snap install gnome-logs
sudo snap install gnome-system-monitor

Simply repeat this process, or use the graphical Ubuntu Software for the additional snaps such as communititheme, vlc and others.