primary device changing from boot to boot

[Tim Harvey]

On Tue, Sep 5, 2017 at 9:56 AM, Pičugins Arsenijs <crimier at yandex.ru> wrote:
> I don't know if it's going to help you with this issue, but if you can hardcode a path to the serial port somewhere, take a look in the "/dev/serial/by-id" directory - it has symlinks to /dev/tty* entries that correspond to hardware serial ports currently connected. Names of the symlinks are generated from some kind of hardware IDs, so should be the same, no matter the order of enumeration (unless your hardware doesn't expose an unique ID that udev, or whatever makes those symlinks, could use)
>

It is true that the symlinks in /dev/serial/by-id are constant but I
don't know how to get nm to use them as nmcli is particularlly finiky
about what is allowed for the 'ifname' param.

root at ventana:~# ls /dev/serial/by-id/
usb-Sierra_Wireless_Inc._HL7xxx_014284000070452-if00
usb-Sierra_Wireless_Inc._HL7xxx_014284000070452-if02
usb-Sierra_Wireless_Inc._HL7xxx_014284000070452-if04

root at ventana: ~# nmcli connection add type gsm ifname
"usb-Sierra_Wireless_Inc._HL7xxx_014284000070452-if00" con-name
mymodem apn vzwinternet
Error: 'ifname':
'usb-Sierra_Wireless_Inc._HL7xxx_014284000070452-if00' is not a valid
interface nor '*'.

root at ventana: ~# nmcli connection add type gsm ifname
"/dev/serial/by-id/usb-Sierra_Wireless_Inc._HL7xxx_014284000070452-if00"
con-name mymodem apn vzwinternet
Error: 'ifname':
'usb-Sierra_Wireless_Inc._HL7xxx_014284000070452-if00' is not a valid
interface nor '*'.

I'm not sure what the rules are for ifname for type gsm... seems to
accept 'foo', but apparently not just anything.

Tim