PySerial could not open port COM4: [Error 5] Access is denied - please help

[Adam]

"Paul" <nospam at needed.com> wrote in message 
news:jseu9c$sp3$1 at dont-email.me...
> Adam wrote:
>> "John Nagle" <nagle at animats.com> wrote in message 
>> news:jse604$1cq$1 at dont-email.me...
>>> On 6/26/2012 9:12 PM, Adam wrote:
>>>> Host OS:    Ubuntu 10.04 LTS
>>>> Guest OS:    Windows XP Pro SP3
>>>>
>>>>
>>>> I am able to open port COM4 with Terminal emulator.
>>>>
>>>> So, what can cause PySerial to generate the following error ...
>>>>
>>>> C:\Wattcher>python wattcher.py
>>>> Traceback (most recent call last):
>>>>    File "wattcher.py", line 56, in <module>
>>>>      ser.open()
>>>>    File "C:\Python25\Lib\site-packages\serial\serialwin32.py", line 56, 
>>>> in
>>>> open
>>>>      raise SerialException("could not open port %s: %s" % 
>>>> (self.portstr,
>>>> ctypes.WinError()))
>>>> serial.serialutil.SerialException: could not open port COM4: [Error 5]
>>>> Access is denied.
>>>     Are you trying to access serial ports from a virtual machine?
>>> Which virtual machine environment?  Xen?  VMware? QEmu?  VirtualBox?
>>> I wouldn't expect that to work in most of those.
>>>
>>>     What is "COM4", anyway?   Few machines today actually have four
>>> serial ports.  Is some device emulating a serial port?
>>>
>>> John Nagle
>>>
>>
>> Thanks, and yes, I am using VirtualBox.  My laptop does not have a serial 
>> port so
>> I use a USB-to-serial converter, which is assigned COM4.
>>
>
> Doesn't VirtualBox allow "remapping" serial ports ? I thought you
> could have COM 4 in the host OS, and make it COM 1 or COM 2 in
> the guest. Something like that.
>
> http://virtuatopia.com/images/6/60/Virtualbox_serial_port_settings.jpg
>
> Also, Windows (as a host), is notorious for stealing control of
> COM ports. Even Windows software, when you run it, would report
> "COM 4 is busy". Then, you have to track down *why* it's busy.
> Is it that FAX software you installed ? The GPS software
> that talks to your GPS serial interface ?
>
> In theory, the "Handle" program is supposed to identify what
> is keeping a COM port busy, but I don't get the desired
> results from it very often. You need to know the naming
> convention for virtual COM ports (COM4 via USB to serial, is
> more virtual than physical). That's what makes it harder
> to track down.
>
> These are some names for COM ports, in Windows. The last two entries,
> are my USB to serial adapters. VCP1 functions as COM3.
> VCP0 functions as COM4. The VCP part is what would be
> listed in "Handle" from Sysinternals. The \device\serial
> format, is more likely to be used with true "native"
> motherboard serial ports.
>
>    \device\serial
>
>    ups.exe pid: 1072 NT AUTHORITY\SYSTEM
>       98: File  (---)   \Device\VCP0
>    hypertrm.exe pid: 3404 ComputerName\UserID     (claims to use COM3)
>       E0: File  (---)   \Device\VCP1
>
> You can download "Handle" and play with it here.
>
> http://technet.microsoft.com/en-us/sysinternals/bb896655
>
> Note that, in my Handle results, at the time I was running
> the Windows provided ups.exe to talk to my external UPS
> (uninterruptible power supply). So that's what that
> reference is. The "hypertrm" one, is me using the
> built-in Windows terminal software, to talk to COM3,
> to keep the port artificially busy for the purposes
> of testing.
>
> If things were working well in your case, you *might*
> see something of this form. If not, you'd instead
> see the name of the process that has "stolen" the
> com port.
>
>    virtualbox.exe pid: 1234 ComputerName\UserID
>       E0: File  (---)  \Device\VCP0
>
> HTH,
>    Paul


Thanks (Guru Paul), I've been using the USB-to-serial converter successfully 
without
enabling/remapping via VBox Settings=>Serial Ports (which are both "not" 
enabled).
I can see the serial port COM4 under Device Manager though.  So, maybe 
enabling is
necessary when the host has "native" serial ports, which my laptop does not 
have.

>From the output generated by Handle.exe, here's the section for TeraTerm ...
------------------------------------------------------------------------------
ttermpro.exe pid: 596 VBOX_WINXPPRO\adam        (claims to use COM4)
    C: File  (RW-)   D:\downloads\Tera Term Pro\ttpro313
   2C: Section       \BaseNamedObjects\ttset_memfilemap
   44: File  (RW-) 
C:\WINDOWS.0\WinSxS\x86_Microsoft.Windows.Common-Controls_6595b64144ccf1df_6.0.2600.6028_x-ww_61e65202
   54: File  (RW-) 
C:\WINDOWS.0\WinSxS\x86_Microsoft.VC80.CRT_1fc8b3b9a1e18e3b_8.0.50727.6195_x-ww_44262b86
   70: Section 
\BaseNamedObjects\_ISWINTERNAL_EPT32_SHEX_K32_0_1c9aa25ea688500_7c80_S-1-5-21-1801674531-1078145449-1957994488-1004
   78: File  (RWD)   C:\DOCUME~1\adam\LOCALS~1\Temp\IswTmp\Logs\ISWSHEX.swl
   AC: Section 
\BaseNamedObjects\_ISWINTERNAL_EPT32_SHEX_A32_0_1c98aa70f70ec00_77dd_S-1-5-21-1801674531-1078145449-1957994488-1004
  100: Section 
\BaseNamedObjects\CiceroSharedMemDefaultS-1-5-21-1801674531-1078145449-1957994488-1004
  108: File  (RW-)   D:\downloads\Tera Term Pro\ttpro313\httplog.log
  120: Section 
\BaseNamedObjects\CTF.TimListCache.FMPDefaultS-1-5-21-1801674531-1078145449-1957994488-1004SFM.DefaultS-1-5-21-1801674531-1078145449-1957994488-1004
  128: Section       \BaseNamedObjects\ShimSharedMemory
  138: Section       \BaseNamedObjects\MSCTF.Shared.SFM.IAB
------------------------------------------------------------------------------