Στις 09-08-2010, ημέρα Δευ, και ώρα 09:13 +0200, ο/η Helmut Lichtenberg
έγραψε:
> Alkis Georgopoulos schrieb am 06. Aug 2010 um 15:44:16 CEST:
> > You can put an extra `exec` at the last line of /usr/sbin/nbdrootd so
> > that no nbdrootd processes exist at all:
> > PATH=/usr/bin:/bin:$PATH exec nbd-server 0 $1 -r -C /dev/null $nbd_timeout
> > > /dev/null 2>&1
>
> Can somebody explain, how this funny nbd works?
In a 10.04 default installation:
* the client runs nbd-proxy to connect to the server
* and then nbd-client to connect to nbd-proxy locally
* the server openbsd-inetd receives the connection and runs nbdrootd
* nbdrootd is just a script that loads nbd-server with the appropriate
parameters
- so, after invoking the script, you can just kill it, it doesn't do
anything more. That's exactly what the "exec" thing above does.
It was also pushed upstream recently.
* nbd-server finally serves the image
Now, suppose that the server reboots.
* if a user is logged in, the ssh connection will be broken, and the
client will hang.
* if no user is logged in then nbd-proxy will keep trying to reconnect
until the server is up again. So as far as nbd-client is concerned,
the connection never broke.
* in previous Ubuntu versions, where nbd-proxy was not used, if no
user was logged in, and the client asked for some nbd data (e.g. some
cron command trying to access the disk) then it would hang.
Hope this clears up things a little bit,
Alkis
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