Samba client behaviour during a fault condition?

[Luke Kenneth Casson Leighton]

hi richard,

there are probably better people to answer your questions here than i, 
but i'll have a go anyway.  if anyone else knows the answers to these, 
can you also reply?  ta!

On Mon, 13 Oct 1997, Richard Roberto wrote:

> Hi, I'm using Samba 1.9.17p1 on Solaris 2.5.1 and connecting with
> both NT and '95 clients.  I'm looking for info on fault conditions.
> I read as many docs as I could and skimmed the rest, but it would be
> a lot easier if someone could give me a pointer to the right place.
> The questions I need to answer are:
> 
> What happens if the samba server crashes (and reboots) during a
> client write (i.e. what state is the client left in?, can it recover
> the session and complete the write?, if so, what's the timeout value
> before this is no linger the case?)

it's up to the client, and it's also dependent on the state of the server 
when it crashes and reboots.


SMB is supposed to be resilient.  twin machines, with dual RAID access 
have been known to crash: the backup take over, and no disruption (other 
than a "access error: abort, retry, cancel" dialog box) occurred.  the 
original poster reported this about... eighteen months ago, and also 
described in detail the architecture of their twin server: have a look 
on the digest archives.  the disruption to file transfer occurred while 
the user was installing NT :-)

the CIFS spec states that the server can drop the connection at any time,
and the client should re-connect.  this turns out to be a bit idealistic. 
while the client is in the middle of _certain_ operations, the connection 
can be dropped.

it really depends on the client, therefore.  clients actually have to be 
more complex than servers, although smbfs is only 2,500 lines of code.


regarding the server, if the server is in a bad way when it crashed, then 
getting samba running again on it is going to be the least of your worries.


> What state is the server left in if the client gags during a write
> (or a read for that matter)?  Essentially, if a PC (or net
> connection) dies and doesn't gracefully terminate its net
> connections, how does the sabma server behave?

it's a TCP connection.  therefore, it depends on the server OS.  sunos
4.1.3 waits for a couple of minutes before realising that the TCP
connection has died.

once the TCP connection goes, the smbd process _specific_ to that 
client should also go.

> One more thing, if one of our clients connects to the service using
> "\\servername\service" syntax, then the connection never reconnects
> after a samba server reboot.

?

>  It does so with no problems if we use
> "\\serverip\service".  We use DNS for name resolution.  The error we
> get is the infamous error 53 "network path not found".  This I
> haven't fully researched, I admit, but since I'm posting anyway ...

ok.  what clients are you using?  i take it that you are using "dns proxy 
= yes", which is the default for 1.9.17, as you can't use DNS resolution 
for w95.

you'd be advised to do read the DIAGNOSIS.txt, to do a tcpdump, and also
you'll need to get some further info on this.  for example: 

- are you using WINS on all your clients?
- are you configuring samba as a WINS server, or using other WINS servers?
- is your network subdivided into broadcast-isolated subnets?
- are you using broadcast-forwarding?
- are you using protocols other than tcp/ip?
- are you using NT SP3?
- are you using w95 OSR/2?

etc.

send your smb.conf file to the list if you don't resolve this soon.  
remember to change any names and remove any ip addresses (put x.x.x.1 
instead).


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i like your .signature.  how much did it cost nat west in lawyer's fees?

:-)


<a href="mailto:lkcl at switchboard.net"  > Luke Kenneth Casson Leighton </a>
<a href="http://mailhost.cb1.com/~lkcl"> Lynx2.7-friendly Home Page   </a>
<br><b>  "Apply the Laws of Nature to your environment before your
          environment applies the Laws of Nature to you"              </b>