Re: Resetting USB modems and USB to serial converters increases ttyUSBXX counter

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Dan Williams <dcbw@xxxxxxxxxx> writes:
> On Thu, 2015-10-22 at 10:39 +0200, Erwin Van de Velde wrote:
>> Hi all,
>> 
>> Thank you for your helpful answers! I have investigated it further,
>> stopping potential culprits in userspace and I have found the issue:
>> it is modemmanager that seems to keep the devices open somewhere and
>> thus causes the ttyUSB numbers to go up. So now I will redirect the
>> issue to their developers :-)
>
> There was a bug between ModemManager 1.2 and 1.4.2 that could have
> triggered this, which was fixed in commit
> 009af02f6d06d5020e397455354b9ccc56557b02.  So make sure you have 1.4.2
> (released on 13-Jan-2015) or later.

Yes, unfortunately that includes the current Debian stable version:

nemi:/home/bjorn# apt-cache policy modemmanager
modemmanager:
  Installed: 1.4.0-1
  Candidate: 1.4.0-1
  Version table:
     1.4.12-1 0
        600 http://ftp.no.debian.org/debian/ sid/main amd64 Packages
 *** 1.4.0-1 0
        700 http://ftp.no.debian.org/debian/ jessie/main amd64 Packages
        100 /var/lib/dpkg/status


nemi:/home/bjorn# lsof -p8191|grep /dev
ModemMana 8191 root    0u      CHR             136,14      0t0       17 /dev/pts/14
ModemMana 8191 root    1u      CHR             136,14      0t0       17 /dev/pts/14
ModemMana 8191 root    2u      CHR             136,14      0t0       17 /dev/pts/14
ModemMana 8191 root    9u      CHR              180,0      0t0  1091872 /dev/cdc-wdm0
ModemMana 8191 root   10u      CHR              166,0      0t0     9804 /dev/ttyACM0 (deleted)
ModemMana 8191 root   11u      CHR              166,1      0t0   397155 /dev/ttyACM1 (deleted)
ModemMana 8191 root   12u      CHR              166,2      0t0   448536 /dev/ttyACM2 (deleted)
ModemMana 8191 root   13u      CHR              166,3      0t0   507569 /dev/ttyACM3 (deleted)
ModemMana 8191 root   14u      CHR              166,4      0t0   673258 /dev/ttyACM4 (deleted)
ModemMana 8191 root   15u      CHR              166,5      0t0   922024 /dev/ttyACM5 (deleted)


I must admit that I have known about this, but have been too lazy to
report it against the Debian package.  It doesn't cause any real
problems for me, even if I sometimes do large numbers of modem
plug/unplug cycles. I just restart ModemManager if I find the device
numbers too high :)



Bjørn
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