I'm using the script from https://devzone.nordicsemi.com/f/nordic-q-a/53208/updating-nrf9160-modem-firmware-through-the-command-line/215357#215357
Under strace, it never forks any other process and doesn't create the file it's looking for, so I'm really not sure what it's expecting to happen.
Full strace at http://triffid-hunter.no-ip.info/pynrf-flash.strace since this forum thing keeps throwing errors when I try to attach it.
https://devzone.nordicsemi.com/f/nordic-q-a/62397/nrfjprog-bug-gets-stuck-due-to-temporary-directory-permissions seems related however my permissions are fine, and the directory tree in /tmp is recreated identically if I wipe it first.
Since this is apparently the only way to update the NRF91 modem firmware from a terminal, and all the examples seem to be complaining about out-of-date modem firmware, I'm once again stuck.