(this might worth a Sticky post option)

Ubuntu 10.04.1 X86_64
smstools 3.1.14 installed from sources
FALCOM TANGO 55 modem (RS-232) through a dual RS-232/USB adapter (serial ports are not that easy to find on today's motherboards)
Relay/opto unit connected to USB port.

Hi all,

Drivers are well loaded and devices are mounted on /dev/ttyUSB0 /dev/ttyUSB1 /dev/ttyUSB2.
dmesg | grep ttyUSB [ 32.170295] usb 7-1: Moschip 2 port adapter converter now attached to ttyUSB1 [ 32.170325] usb 7-1: Moschip 2 port adapter converter now attached to ttyUSB2 [ 32.171798] usb 5-1: FTDI USB Serial Device converter now attached to ttyUSB0

The bad thing is that the mount points (/dev/ttyUSBx) are changing after a reboot, so it isn't possible to declare device = /dev/ttyUSB1 in /etc/smsd.conf

The way is to use udev to declare personal mount points.
Display the devices specifications: (Code between *** *** is used for the udev rules)
sudo udevadm info --query=all --name=ttyUSB0 P: /devices/pci0000:00/0000:00:1a.2/usb5/5-1/5-1:1.0/ttyUSB0/tty/ttyUSB0 N: ttyUSB0 S: char/188:0 S: serial/by-path/pci-0000:00:1a.2-usb-0:1:1.0-port0 S: serial/by-id/usb-FTDI_AUDON_UDIN-44_USB_Relay_Opto_Unit_A4SG9MRO-if00-port0 E: UDEV_LOG=3 E: DEVPATH=/devices/pci0000:00/0000:00:1a.2/usb5/5-1/5-1:1.0/ttyUSB0/tty/ttyUSB0 E: MAJOR=188 E: MINOR=0 E: DEVNAME=/dev/ttyUSB0 E: SUBSYSTEM=tty E: ID_PORT=0 E: ID_PATH=pci-0000:00:1a.2-usb-0:1:1.0 E: ***ID_VENDOR=FTDI*** E: ID_VENDOR_ENC=FTDI E: ID_VENDOR_ID=0403 E: ID_MODEL=AUDON_UDIN-44_USB_Relay_Opto_Unit E: ID_MODEL_ENC=AUDON\x20UDIN-44\x20USB\x20Relay\x2fOpto\x20Unit E: ID_MODEL_ID=6001 E: ID_REVISION=0600 E: ***ID_SERIAL=FTDI_AUDON_UDIN-44_USB_Relay_Opto_Unit_A4SG9MRO*** E: ID_SERIAL_SHORT=A4SG9MRO E: ID_TYPE=generic E: ID_BUS=usb E: ID_USB_INTERFACES=:ffffff: E: ID_USB_INTERFACE_NUM=00 E: ID_USB_DRIVER=ftdi_sio E: ID_IFACE=00 E: ID_VENDOR_FROM_DATABASE=Future Technology Devices International, Ltd E: ID_MODEL_FROM_DATABASE=FT232 USB-Serial (UART) IC E: DEVLINKS=/dev/char/188:0 /dev/serial/by-path/pci-0000:00:1a.2-usb-0:1:1.0-port0 /dev/serial/by-id/usb-FTDI_AUDON_UDIN-44_USB_Relay_Opto_Unit_A4SG9MRO-if00-port0

(Code between *** *** is used for the udev rules)
sudo udevadm info --query=all --name=ttyUSB1 P: /devices/pci0000:00/0000:00:1d.1/usb7/7-1/7-1:1.0/ttyUSB1/tty/ttyUSB1 N: ttyUSB1 S: char/188:1 S: serial/by-path/pci-0000:00:1d.1-usb-0:1:1.0-port0 S: serial/by-id/usb-9710_7720-if00-port0 E: UDEV_LOG=3 E: DEVPATH=/devices/pci0000:00/0000:00:1d.1/usb7/7-1/7-1:1.0/ttyUSB1/tty/ttyUSB1 E: MAJOR=188 E: MINOR=1 E: DEVNAME=/dev/ttyUSB1 E: SUBSYSTEM=tty E: ***ID_PORT=0*** E: ID_PATH=pci-0000:00:1d.1-usb-0:1:1.0 E: ***ID_VENDOR=9710*** E: ID_VENDOR_ENC=9710 E: ID_VENDOR_ID=9710 E: ***ID_MODEL=7720*** E: ID_MODEL_ENC=7720 E: ID_MODEL_ID=7720 E: ID_REVISION=0100 E: ID_SERIAL=9710_7720 E: ID_TYPE=generic E: ID_BUS=usb E: ID_USB_INTERFACES=:ff00ff: E: ID_USB_INTERFACE_NUM=00 E: ID_USB_DRIVER=moschip7720 E: ID_IFACE=00 E: ID_VENDOR_FROM_DATABASE=MosChip Semiconductor E: DEVLINKS=/dev/char/188:1 /dev/serial/by-path/pci-0000:00:1d.1-usb-0:1:1.0-port0 /dev/serial/by-id/usb-9710_7720-if00-port0

(Code between *** *** is used for the udev rules)
sudo udevadm info --query=all --name=ttyUSB2 P: /devices/pci0000:00/0000:00:1d.1/usb7/7-1/7-1:1.0/ttyUSB2/tty/ttyUSB2 N: ttyUSB2 S: char/188:2 S: serial/by-path/pci-0000:00:1d.1-usb-0:1:1.0-port1 S: serial/by-id/usb-9710_7720-if00-port1 E: UDEV_LOG=3 E: DEVPATH=/devices/pci0000:00/0000:00:1d.1/usb7/7-1/7-1:1.0/ttyUSB2/tty/ttyUSB2 E: MAJOR=188 E: MINOR=2 E: DEVNAME=/dev/ttyUSB2 E: SUBSYSTEM=tty E: ***ID_PORT=1*** E: ID_PATH=pci-0000:00:1d.1-usb-0:1:1.0 E: ***ID_VENDOR=9710*** E: ID_VENDOR_ENC=9710 E: ID_VENDOR_ID=9710 E: ***ID_MODEL=7720*** E: ID_MODEL_ENC=7720 E: ID_MODEL_ID=7720 E: ID_REVISION=0100 E: ID_SERIAL=9710_7720 E: ID_TYPE=generic E: ID_BUS=usb E: ID_USB_INTERFACES=:ff00ff: E: ID_USB_INTERFACE_NUM=00 E: ID_USB_DRIVER=moschip7720 E: ID_IFACE=00 E: ID_VENDOR_FROM_DATABASE=MosChip Semiconductor E: DEVLINKS=/dev/char/188:2 /dev/serial/by-path/pci-0000:00:1d.1-usb-0:1:1.0-port1 /dev/serial/by-id/usb-9710_7720-if00-port1

Create the personal mount points from device specifications:
sudo nano /etc/udev/rules.d/usb.rules SUBSYSTEM=="tty", SUBSYSTEMS=="usb", ENV{ID_VENDOR}=="FTDI", ENV{ID_SERIAL}=="FTDI_AUDON_UDIN-44_USB_Relay_Opto_Unit_A4SG9MRO", SYMLINK+="myttyUSB0" SUBSYSTEM=="tty", SUBSYSTEMS=="usb", ENV{ID_VENDOR}=="9710", ENV{ID_MODEL}=="7720", ENV{ID_PORT}=="0", SYMLINK+="myttyUSB1" SUBSYSTEM=="tty", SUBSYSTEMS=="usb", ENV{ID_VENDOR}=="9710", ENV{ID_MODEL}=="7720", ENV{ID_PORT}=="1", SYMLINK+="myttyUSB2"

You need to reboot or unplug/replug USB devices to make changes effective.
Check the mountpoints:
ls -lh /dev/my* lrwxrwxrwx 1 root root 7 2010-11-24 09:56 /dev/myttyUSB0 -> ttyUSB0 lrwxrwxrwx 1 root root 7 2010-11-24 09:56 /dev/myttyUSB1 -> ttyUSB1 lrwxrwxrwx 1 root root 7 2010-11-24 09:56 /dev/myttyUSB2 -> ttyUSB2

Now you just need to use /dev/myttyUSB1 (adjust for your configuration) in /etc/smsd.conf, the modem will be recognized where-ever it is plugged in USB ports.

Hope this will help some