Does anyone know, or is there documentation describing Windows timeout values for Read and Write via SMB?

Christopher R. Hertel crh at
Sun Dec 2 16:04:31 MST 2012

On 12/02/2012 03:45 PM, Richard Sharpe wrote:
>>From MS-CIFS:
> <189> Section Windows NT and Windows 98 CIFS clients
> periodically scan for any commands that have not completed.  The
> default scanning period is 30 seconds.  If there are outstanding
> commands that have exceeded the Client.SessionTimeoutValue, an
> SMB_COM_ECHO (section is sent to determine whether or
> not the connection has been lost. The client closes the
> connection only if there is no response to the echo request.
> ------------------------
> Other documentation claims that the number is 32 seconds. I have seen
> 48 second, I think, on the wire. Will have to check that last number.

That does indeed sound like my writing.  :)

The note you've copied above talks about the conditions under which
the connection is closed.  If the SMB_COM_ECHO returns successfully, then
we know that the connection is still good but the operation has timed out.
There should be a description explaining what the client does in this case.
 Somewhere.  If it's not there, then you've got a very good question for the
Microsoft folks.

Also not that if the Client.SessionTimeoutValue is exceeded just *after* a
scan occurs, then the timeout won't be caught until the scan occurs, so
there is a good deal of variability in the actual amount of time after which
the expired command will be caught and acted upon.

Client.SessionTimeOutValue < actual timeout < Client.SessionTimeOutValue + n

...where n is the scan period, which could vary a lot as well if it is not a
particularly accurate timer.

Chris -)-----
PS.  If I wrote 30 seconds, that's probably what's in the source code.

"Implementing CIFS - the Common Internet FileSystem" ISBN: 013047116X
Samba Team --     -)-----   Christopher R. Hertel
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