Some distros do not allow users access to USB devices by default. If you think this might be the case for you, run the following:

# Allow access to serial devices
adduser <your username> dialout

# Allow access to other USB devices
adduser <your username> plugdev

# Set SWD debugger to access by plugdev group
echo 'SUBSYSTEM=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="3748", MODE="0660", GROUP="plugdev"' > /etc/udev/rules.d/49-ecsc.rules

# Now log out and log in again, or run `newgrp -` to load groups only in the current shell