Ubuntu: avrdude: ser_open():: can't open device "-b57600"

I can’t get arduino to flash on Ubuntu.
I have installed 1.8.5 into /usr/local, and downloaded all the firmware, etc.
Running ‘make flash’ fails with

avrdude: ser_open(): can't open device "-b57600": No such file or directory

the keyboard is apparently available on ttyACM0:

  [ 1328.524791] usb 4-1: Manufacturer: Keyboardio
  [ 1328.524793] usb 4-1: SerialNumber: Ckbio01E
  [ 1328.526948] cdc_acm 4-1:1.0: This device cannot do calls on its own. It is not a modem.
  [ 1328.526999] cdc_acm 4-1:1.0: ttyACM0: USB ACM device

It’s a modem problem on Ubuntu. See here: Flashing problem on Ubuntu (SOLVED)

Thank you. For the record, my problem was embarassingly simple - I wasn’t holding down the ‘Prog’ key…

Looking at that error message again, it’s clear that $DEVICE_PORT_BOOTLOADER didn’t get set, and that argument to avrdude was unquoted, so you got a cryptic error message. We can definitely improve the error reporting here.