I am working with GSM modem and using
Device is having proper rights:
$ ls -alh /dev/ttyUSB2 crw-rw---- 1 root dialout 188, 2 May 25 19:44 /dev/ttyUSB2
I am in
dialout group and I can send AT command to this modem only once. After sending “ATD” command (
echo -e -n "ATD ...;r" > /dev/ttyUSB2), according to
lsof /dev/ttyUSB2 process
ModemManager opens this very file and if I send another AT command I get message:
bash: /dev/ttyUSB2: Device or resource busy
OK, so for some reason ModemManager is holding this file busy, but when this happens I can still send commands the same way, but from
I’ve got two questions:
- Why root user can override this “Device or resource busy” lock?
- What rights / other settings regular user should have to bypass it like root user.