How to open up serial terminal for my USB device converter (or, how to enable VCP in linux)?
please check the permissions of the /dev node

$ls -la /dev/ttyUSB0


There is a high chance it shall resemble

crw-rw----. 1 root dialout 188, 0 Jul 18 13:27 /dev/ttyUSB0


A character device with RW permissions for ROOT and RW permissions for dialout group.

If this is the case check the group membership of the user attempting to access

$ groups


if the user is not part of the dialout group, add them 

$ sudo usermod -a -G dialout $username


The user then needs to logout and log back into reload the group permissions