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Is there any port monitoring tool to watch the packets written on the port? I especially want to check if my program written in Java works so I need some kind of tool to see if my little application is writing the messages to the port. How do I do this?

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20

I found projects called Linux Serial Sniffer, jpnevulator, and Moni. The first two look like they do exactly what you want. The last one calls itself a monitor, but it actually looks like a standard serial communication program.

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    thanks for that !! i will give it a try. by the way i solved the issue from my java side. i was missing a \r, so that prevented my message from writing on to the port. thanks for that anyways!! – Deepak Apr 30 '11 at 18:24
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    The «LInux Serial Sniffer» is buggy, it absolutely takes out incoming data, thus another application which is actually listen to serial see nothing. But, at least, the data that goes outside seems to go without problem. – Hi-Angel Mar 31 '15 at 11:12
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    From the jpnevulator FAQ: "Jpnevulator was never built to sit in between the kernel and your application." – Shelvacu Jun 12 '17 at 2:14
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    The link referring to Moni is dead. – Yaron Dec 12 '18 at 15:24
28

is a tool to connect (nearly) everything to (nearly) everything, and can duplicate streams.
In your usecase you could connect your serial port /dev/ttyS0 to a PTY /tmp/ttyV0, then point your application to the PTY, and have socat tee out Input and Output somewhere for you to observe.

Googling "socat serial port pty tee debug" will point you to several examples, one being:

socat /dev/ttyS0,raw,echo=0 \
SYSTEM:'tee in.txt |socat - "PTY,link=/tmp/ttyV0,raw,echo=0,waitslave" |tee out.txt'

The files in.txt and out.txt will then contain the captured data.

This has been confirmed to work by commenters (@ogurets).

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    Just tried it and have both input and output recorded. Socat version "1.7.2.4+sigfix" from Debian Jessie packages. – ogurets May 17 '17 at 21:41
  • The idea is good, but not even socat can proxy ioctl calls. – peterh Jan 24 at 13:34
15

I don't think the serial driver has any tracing functionality that would allow you to watch packets. You can use strace to observe all the reads and writes from your application:

strace -s9999 -o myapp.strace -eread,write,ioctl ./myapp
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    can is send packets to the port if nothign is connected ? – Deepak Apr 30 '11 at 12:53
  • strace will tell you if it tried to send characters to the port, and what the kernel responded with when it tried. depending on your flow control settings characters may arrive at the disconnected TXD pin or may not. – Jasen Jun 28 '18 at 5:19
3

When I debug interaction of my application with a serial port, I use moserial.

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    What're you talking about, in the docs written it's just a terminal. – Hi-Angel Mar 31 '15 at 10:53
3

Try this:

screen /dev/tty.usbserial-blahblah 9600

works for me.

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    This opens the port and assumes control over it, so nothing else can use it. This does not "monitor" or "sniff" the traffic. – Ian M Jan 23 '15 at 7:12
3

interceptty does that job:

interceptty /dev/ttyACM0 /dev/ttyDUMMY

or, with a nice output format and with configuring the backend device, and with line buffering:

interceptty -s 'ispeed 19200 ospeed 19200' -l /dev/ttyACM0 /dev/ttyDUMMY | interceptty-nicedump

and then connect with your programme to /dev/ttyDUMMY.

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1

Have a look at ttyUSBSpy. It is on alpha stage, but it works.

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    It doesn't. It is written in python, and the code does import some import pcopy, which is even Google gave up to find. – Hi-Angel Mar 31 '15 at 10:43
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    Software/Homepage looks abandoned. Is not in package managers. – Alex Stragies Apr 16 '17 at 16:28
1

minicom is missing from the list of tools to monitor serial ports. Use it as for example to listen to arduino device:

minicom --device /dev/ttyACM0 --baud 9600

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  • OP wrote "monitor", but meant "sniffer" ( = is able to read traffic in transit), while minicom is a serial port "client", and as such is not an answer to this question. The answer below from mike made the same mistake, and the comment there explains the terminology problem as well. – Alex Stragies Mar 17 at 21:03

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