How to fix slow shutdown / restart of Ubuntu 18.04

Sometimes, Ubuntu 18.04 system hangs or takes very long time to shutdown.

We can fix this by editing the system.conf file.

For example,

$ sudo gedit /etc/systemd/system.conf

Change the DefaultTimeoutStopSec section to around 4 or 5 seconds.

#DefaultTimeoutStopSec=90s
DefaultTimeoutStopSec=4s

Save the file, and reboot. :)