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We have an Hylafax 5.2.5 CentOS 5 installation hosted inside a Xen virtual machine. It works quite well, but now I'm in the process of upgrading/migrating it to a KVM virtual machine running Ubuntu 10.04 and Hylafax 5.5.1 (compiled from source using )

The problem I'm having is that - while receiving works fine - sending faxes is extremely unreliable, I get lots of "No response to MPS repeated 3 tries", or "Failure to transmit clean ECM image data."

The line, modem and configuration files I'm using are the same as before, so I thought that it could be a KVM scheduling issue, but even setting cpu_shares to 10240 instead of 1024 doesn't change a thing... What else could I try?

Here's an example log file

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How exactly is the "modem" connected (physical RS232, USB, USB that really uses an USB UART, PCI card?) – rackandboneman May 7 '12 at 0:19
@rackandboneman: it's a physical RS232 (the machine is a Dell 110T II) – Joril May 8 '12 at 13:16

I would suggest you first verify your rs232 subsystem is up to spec, eg by sending data through the virtualised serial port out the physical connection to another machine and looking for stalls and/or data errors. Also, try fiddling with the baud rate.

I hate to suggest twice in a week on SE that someone find an oscilloscope, but it can be very revealing with RS232 problems...

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