Operating system name and version: Rocky Linux 8.8
Version of smsd: Smsd v3.1.21
Smsd installed from: smstools3-3.1.21.tar.gz
Name and model of a modem / phone: QUECTEL Mobile Broadband Module
Interface: USB

I've connected this USB-modem to our new nagios-server for sending SMS-alerts.
Same model already works on older nagios-server with CentOS 7.9 and smstools.
But on Rocky 8.8 there are no replies to the AT-commands (same smsd.conf like on older nagios-server).
I've tried with all ttyUSBx in smsd.conf
But I can send and received SMS with mmcli (ModemManager).
So it seems all the drivers are installed.

messages:Sep 14 14:06:12 nagios02 kernel: usb 1-13: GSM modem (1-port) converter now attached to ttyUSB0 messages:Sep 14 14:06:12 nagios02 kernel: usb 1-13: GSM modem (1-port) converter now attached to ttyUSB1 messages:Sep 14 14:06:12 nagios02 kernel: usb 1-13: GSM modem (1-port) converter now attached to ttyUSB2 messages:Sep 14 14:06:12 nagios02 kernel: usb 1-13: GSM modem (1-port) converter now attached to ttyUSB3 messages:Sep 14 14:06:19 nagios02 ModemManager[2024]: <warn> [ttyUSB0/probe] failed to parse QCDM version info command result: -7 smsd.log 2023-09-14 20:44:34,2, smsd: Smsd v3.1.21 started. 2023-09-14 20:44:34,2, smsd: Running as root:root (0:0). 2023-09-14 20:44:34,7, smsd: Running startup_check (shell): /var/spool/sms/incoming/smsd_script.bSxKks /tmp/smsd_data.ahtfRS 2023-09-14 20:44:34,7, smsd: Done: startup_check (shell), execution time 0 sec., status: 0 (0) 2023-09-14 20:44:34,4, smsd: File mode creation mask: 022 (0644, rw-r--r--). 2023-09-14 20:44:34,5, smsd: Outgoing file checker has started. PID: 2502605. 2023-09-14 20:44:34,7, smsd: All PID's: 2502605,2502607 2023-09-14 20:44:34,5, GSM1: Modem handler 0 has started. PID: 2502607. Will only send messages. 2023-09-14 20:44:34,6, GSM1: Checking if modem is ready 2023-09-14 20:44:34,7, GSM1: -> AT 2023-09-14 20:44:34,7, GSM1: Command is sent, waiting for the answer. (5) 2023-09-14 20:44:39,7, GSM1: No answer, put_command expected (OK)|(ERROR)|(0)|(4), timeout occurred. 1. 2023-09-14 20:44:39,7, GSM1: <- 2023-09-14 20:44:39,7, GSM1: -> 2023-09-14 20:44:39,7, GSM1: Command is sent, waiting for the answer. (5) 2023-09-14 20:44:44,7, GSM1: No answer, put_command expected (OK)|(ERROR)|(0)|(4), timeout occurred. 2. 2023-09-14 20:44:44,7, GSM1: <- 2023-09-14 20:44:44,7, GSM1: -> AT 2023-09-14 20:44:44,7, GSM1: Command is sent, waiting for the answer. (5) 2023-09-14 20:44:49,7, GSM1: No answer, put_command expected (OK)|(ERROR)|(0)|(4), timeout occurred. 3. 2023-09-14 20:44:49,7, GSM1: <- 2023-09-14 20:44:49,7, GSM1: -> 2023-09-14 20:44:49,7, GSM1: Command is sent, waiting for the answer. (5) 2023-09-14 20:44:54,7, GSM1: No answer, put_command expected (OK)|(ERROR)|(0)|(4), timeout occurred. 4. 2023-09-14 20:44:54,7, GSM1: <- 2023-09-14 20:44:54,7, GSM1: -> AT

OK, the solution was much easier than I thought.
I had to stop ModemManager, then smsd can communicate with the modem over AT-commands.
So it seems not both should run at the same time...
Thanks.

2023-09-17 08:27:27,2, smsd: Smsd v3.1.21 started. 2023-09-17 08:27:27,2, smsd: Running as root:root (0:0). 2023-09-17 08:27:27,7, smsd: Running startup_check (shell): /var/spool/sms/incoming/smsd_script.pK6ce1 /tmp/smsd_data.3IJbAM 2023-09-17 08:27:27,7, smsd: Done: startup_check (shell), execution time 0 sec., status: 0 (0) 2023-09-17 08:27:27,4, smsd: File mode creation mask: 022 (0644, rw-r--r--). 2023-09-17 08:27:27,5, smsd: Outgoing file checker has started. PID: 571157. 2023-09-17 08:27:27,7, smsd: All PID's: 571157,571158 2023-09-17 08:27:27,5, GSM1: Modem handler 0 has started. PID: 571158. Will only send messages. 2023-09-17 08:27:27,6, GSM1: Checking if modem is ready 2023-09-17 08:27:27,7, GSM1: -> AT 2023-09-17 08:27:27,7, GSM1: Command is sent, waiting for the answer. (5) 2023-09-17 08:27:27,7, GSM1: <- AT OK 2023-09-17 08:27:27,6, GSM1: Pre-initializing modem 2023-09-17 08:27:27,7, GSM1: -> ATE0 2023-09-17 08:27:27,7, GSM1: Command is sent, waiting for the answer. (10) 2023-09-17 08:27:27,7, GSM1: <- ATE0 OK 2023-09-17 08:27:27,7, GSM1: -> AT+CMEE=1;+CREG=2 2023-09-17 08:27:27,7, GSM1: Command is sent, waiting for the answer. (10) 2023-09-17 08:27:27,7, GSM1: <- OK 2023-09-17 08:27:27,6, GSM1: Checking if modem needs PIN 2023-09-17 08:27:28,7, GSM1: -> AT+CPIN? 2023-09-17 08:27:28,7, GSM1: Command is sent, waiting for the answer. (10) 2023-09-17 08:27:28,7, GSM1: <- +CPIN: READY OK 2023-09-17 08:27:28,7, GSM1: -> AT+CSQ 2023-09-17 08:27:28,7, GSM1: Command is sent, waiting for the answer. (10) 2023-09-17 08:27:28,7, GSM1: <- +CSQ: 19,99 OK 2023-09-17 08:27:28,6, GSM1: Signal Strength Indicator: (19,99) -75 dBm (Good), Bit Error Rate: not known or not detectable 2023-09-17 08:27:28,6, GSM1: Checking if Modem is registered to the network 2023-09-17 08:27:28,7, GSM1: -> AT+CREG? 2023-09-17 08:27:28,7, GSM1: Command is sent, waiting for the answer. (10) 2023-09-17 08:27:28,7, GSM1: <- +CREG: 2,1,"4271","02EAC33",2 OK 2023-09-17 08:27:28,6, GSM1: Modem is registered to the network