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

Wed Jun 27 12:04:14 EDT 2012

Adam wrote:
> "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
> ------------------------------------------------------------------------------

For Handle to give a positive result, the TeraTerm program would need to
currently have the serial port open. If you haven't started a terminal session,
it might not be listed.

Handle has some kind of filter function, and you can try searching for the name
of the port that way.

I don't see anything in that snipping, which looks like a serial port.

    Paul