How to detect USB Serial port in Ubuntu

first use lsusb command to find:

Mar 25 09:11:26 joelinux kernel: [ 1803.128054] usb 6-1: USB disconnect, address 3
Mar 25 09:11:26 joelinux kernel: [ 1803.128239] pl2303 ttyUSB0: pl2303 converter now disconnected from ttyUSB0
Mar 25 09:11:26 joelinux kernel: [ 1803.128263] pl2303 6-1:1.0: device disconnected
Mar 25 09:11:30 joelinux kernel: [ 1807.632517] usb 6-1: new full speed USB device using uhci_hcd and address 4
Mar 25 09:11:30 joelinux kernel: [ 1807.794123] pl2303 6-1:1.0: pl2303 converter detected
Mar 25 09:11:30 joelinux kernel: [ 1807.806180] usb 6-1: pl2303 converter now attached to ttyUSB0

so you can be sure that kernel has detected the USB port.

Next, detach and re-attach your USB serial device, and look in syslog

1)by System > Administration > System Log Viewer > syslog

or

2) in terminal

>>tail /var/log/syslog

Mar 25 09:11:26 joelinux kernel: [ 1803.128054] usb 6-1: USB disconnect, address 3
Mar 25 09:11:26 joelinux kernel: [ 1803.128239] pl2303 ttyUSB0: pl2303 converter now disconnected from ttyUSB0
Mar 25 09:11:26 joelinux kernel: [ 1803.128263] pl2303 6-1:1.0: device disconnected
Mar 25 09:11:30 joelinux kernel: [ 1807.632517] usb 6-1: new full speed USB device using uhci_hcd and address 4
Mar 25 09:11:30 joelinux kernel: [ 1807.794123] pl2303 6-1:1.0: pl2303 converter detected
Mar 25 09:11:30 joelinux kernel: [ 1807.806180] usb 6-1: pl2303 converter now attached to ttyUSB0