smbd as a daemon

[Andreas Schneider]

On Monday 24 March 2014 09:02:44 you wrote:
> On Mon, Mar 24, 2014 at 05:00:10PM +0100, Andreas Schneider wrote:
> > Hello,
> > 
> > we have an issue with systemd and smbd (maybe also winbind and nmbd).
> > systemd assumes that if the daemon starts up and returns with the exit
> > code SUCCESS that it is ready and working. In a systemd service file
> > normally you specify the PID file which is used to check if a service is
> > running:
> > 
> > systemctl status smb.service
> > 
> > 
> > The problem is that when smbd starts we check if we want to become a
> > daemon. If yes, then we fork and the parent exits with 0. Then we create
> > some directories and create the pid file. So between the exit and the
> > creation of the pid file we have a race condition.
> > 
> > The correct thing would be to wait in the parent util the child is done
> > with the init and then send a signal it can successfully exit.
> > 
> > 
> > The questions what is suggested way to do this inside of smbd?
> > 
> > 
> > Please help!
> 
> Hmmmm. Isn't this breakage inside systemd ? It's common
> for a daemon to start up, fork and then exit to ensure
> you've lost your controlling terminal - make you safe
> to run from the command line as well as from inetd.
> 
> Doesn't this break on many other daemons as well ?

But how do you then tell the process which started you, that the startup was 
successful? We will not remove this, we just wait a bit longer until we 
created the pid file and then exit the parent.

What we have now:

1. You start smbd
2. smbd does exit(0) (hey we started successfully)
3. You check if it is running by checking the pid in /run/smb.pid
4. No pid file has been created yet.
5. We consider smbd isn't running.


What systemd expects:

1. You start smbd
1a. smbd child creates pidfile
1b. smbd child tells parent to exit
2. smbd does exit(0)
3. Checking the pidfile tells us smbd is running.


	-- andreas


-- 
Andreas Schneider                   GPG-ID: CC014E3D
Samba Team                             asn at samba.org
www.samba.org