I posted a thread on the raspberry pi forums, but I believe my problem is too obscure to be helped there. Info below:
I absolutely an unable to get my raspberry pi to open a serial connection to a usb to serial adapter (/dev/ttyusb0) I have even have attempted to use a TTL level shifter and use the GPIO pins (/dev/ttyAMA0)
No matter what, Putty, Minicom, Picocom, are unable to open a serial port connection to the adapter, and subsequently, the terminal node controller (TNC) it is attached to.
I've tried messing with the config file for serial connections.
I have tried PL2303 Prolific chip, FTDI FT232, and an RT Systems usb to DB25 adapter.
I refuse to believe the Pi is not capable of a simple dumb terminal connection. Even IT Dept at work can't figure it out!
Help from a friend:
Not all USB<>Serial adapters are linux compatible. The best ones have the Prolific PL2303 chipset... very plug n play with a Pi or Linux bort ontinue without paging ext Message Continue...c (which is what the Pi runs). The dumb terminal program you probably want to use is called Minicom. There's no com1/com2/etc. You'll need to run at a prompt "ls /dev/ttyU*" and see what USB interface it's grabbed, and then set minicom to use that with full path.
I'm using raspberry Pi 3 B running NOOBS
Pi sees the adapter "bus 004" i@raspberrypi:~ $ lsusb Bus 001 Device 006: ID 04f2:0939 Chicony Electronics Co., Ltd Bus 001 Device 005: ID 04f2:0833 Chicony Electronics Co., Ltd Bus 001 Device 004: ID 0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp. SMSC9512/9514 Fast Ethernet Adapter Bus 001 Device 002: ID 0424:9514 Standard Microsystems Corp. Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub dmesg kernal entries [ 5.153584] usbcore: registered new interface driver usbserial [ 5.153711] usbcore: registered new interface driver usbserial_generic [ 5.153856] usbserial: USB Serial support registered for generic [ 5.167512] usbcore: registered new interface driver ftdi_sio [ 5.167656] usbserial: USB Serial support registered for FTDI USB Serial Device [ 5.167963] ftdi_sio 1-1.2:1.0: FTDI USB Serial Device converter detected [ 5.168202] usb 1-1.2: Detected FT232RL [ 5.172224] usb 1-1.2: FTDI USB Serial Device converter now attached to ttyUSB0
google searching yields little help, I've tried a few coding tricks such as trying to assign a symbolic link to the usb0 and serial port. I've also tried modifying the boot entry to register the usb cable product and vendor ID but I get permission denied. Not sure if those solutions would help.
The system recognizes the ftdi_sio driver and device, which is puzzling. I use PuTTy using default recommended settings, which work on my laptop. I've also used minicom with the same type of failure.
The cables and modem work fine on my Win10 Laptop.