hylafax probemodem fails to probe USB modems

On Ubuntu 21.04 I'm unable to get hylafax 6.0.7 to successfully probe two different USB modems: a USRobotics 5637 and a generic "USB 2.0 56K Modem" with Conexant chipset.

I've gotten hylafax-server installed and appended the following to /etc/udev/rules.d/50-myusb.rules so that Ubuntu would allow writes to the modem:

KERNEL=="ttyUSB[0-9]*",MODE="0666"
KERNEL=="ttyACM[0-9]*",MODE="0666"

1. Is this necessary?

I get the following output when cuing both modems [ttyACM0 is USR5637, ttyACM1 is "USB 2.0 56K Modem"]:

figs@thinkpad:~$ cu -l ttyACM0
Connected.
at+fclass=?
0,1,8

OK
~.

Disconnected.
figs@thinkpad:~$ cu -l ttyACM1
Connected.
at+fclass=?
0,1,1.0,2,8

OK
~.

Disconnected.
figs@thinkpad:~$

• Both modems support Fax Class 1 to work with Hylafax.

Here are the permissions of the two modems, mounted at /dev/:

crw-rw-rw-  1 root dialout 166,     0 Jul 22 19:35 ttyACM0
crw-rw-rw-  1 root dialout 166,     1 Jul 22 19:36 ttyACM1

• Both modems have read & write access and are members of dialout.

When I run probemodem, both modems hang:

figs@thinkpad:/dev$ sudo probemodem
Serial port that modem is connected to []? ttyACM0
Hmm, there does not appear to be an fuser command on your machine.
This means that I am unable to ensure that all processes using the
modem have been killed.  I will keep going, but beware that you may
have competition for the modem.

Now we are going to probe the tty port.  This takes a few seconds,
so be patient.  Note that if you do not have the modem cabled to
the port, or the modem is turned off, this may hang (just go and
cable up the modem or turn it on, or whatever).

Probing for best speed to talk to modem: 38400

• ttyACM0 (USR5637) physical data lights blink briefly, and then this hangs for upwards of 1 day before I give up and kill the process.

• ttyACM1 ("USB 2.0 56K Modem") does the same:

figs@thinkpad:/dev$ sudo probemodem
Serial port that modem is connected to []? ttyACM1
Hmm, there does not appear to be an fuser command on your machine.
This means that I am unable to ensure that all processes using the
modem have been killed.  I will keep going, but beware that you may
have competition for the modem.

Now we are going to probe the tty port.  This takes a few seconds,
so be patient.  Note that if you do not have the modem cabled to
the port, or the modem is turned off, this may hang (just go and
cable up the modem or turn it on, or whatever).

Probing for best speed to talk to modem: 38400

• Both modems respond to the query with cu but will not complete probemodem.

• probemodem declares that fuser is not installed, however I issued the fuser command and it is definitely present despite not appearing in the synaptic gui, or giving any output declaring such from apt-get install fuser.

2. How do I get probemodem to successfully probe the modem? Are permissions messed up somewhere? Elsewhere on the internet are reports of successfully using USR5637... do I need to change something somewhere?

Did I miss something or should this work? I'm sort of a noob at more advanced Linux undertakings and I'm at a loss as to how to get hylafax running with a USB modem.

I'm at the same point right now:

Server: Ubuntu 22.04.1 LTS

The modem US Robotics 5637 does not work with Hylafax 6.0.7!

The server hangs with faxaddmodem just like with probemodem. Both behave exactly the same. If you look at the processes with ps aux | grep modem both programs create the same processes. Only under the respective program name.

faxaddmodem hangs exactly when all requested parameters have been entered and the program wants to access and test the modem for the first time.

You can also start faxaddmodem with the -s switch and specify a speed. E.g. faxaddmodem -s 19200. Then faxaddmodem reports in an endless loop that the modem does not respond and that you should please check what is going on. This loop cannot be interrupted!

The modem is automatically detected and mounted under /dev/ttyACM0. It is immediately ready for use, without any further drivers. With the terminal program minicom you can use it immediately. Establish connections. Incoming calls are signaled.

But Hylafax faxaddmodem hangs, as described above. It helps then only to kill processes and to delete /var/lock/LCK..ttyACM0, otherwise the access to the modem remains blocked. Furthermore, temporary files were created below /tmp/.faxaddmodem or /tmp/.probemodem, which can be removed (without rebooting).

I don't know what to do at the moment either.

Update: In the meantime this USB modem works fine! What was the solution?

Quite simple: Plugging it from an USB3.0 port to an USB2.0 port. The modem then immediately worked with Hylafax as well. Unbelievable! Because it worked with minicom also on an USB3.0 port.

Would have saved me many hours to know this before. So here is my update. Maybe it saves someone else a long search.

Conclusion: The USB modem USR5637 works great under Linux with Hylafax and minicom when connected to an USB2.0 port.