On Nov 29, 2013 1:36 AM, "Cecil Westerhof" <<a href="mailto:Cecil.Westerhof@snow.nl">Cecil.Westerhof@snow.nl</a>> wrote: > > Thanks for the speedy reply. > > > On 11/29/2013 12:30 AM, Mantas Mikulėnas wrote: >> >> On Nov 29, 2013 1:24 AM, "Cecil Westerhof" <<a href="mailto:Cecil.Westerhof@snow.nl">Cecil.Westerhof@snow.nl</a> >> <mailto:<a href="mailto:Cecil.Westerhof@snow.nl">Cecil.Westerhof@snow.nl</a>>> wrote: >> > >> > In a trial presentation I used the following service file: >> > [Unit] >> > Description=Virtual Distributed Ethernet >> > After=syslog.target >> > >> > [Service] >> > Type=forking >> > PIDFile=/var/run/vde.pid >> > # Note the -f: don't fail if there is no PID file >> > ExecStartPre=/bin/rm -f /var/run/vde.pid >> > ExecStart=/usr/bin/vde_switch --tap tap0 --mode 0660 \ >> > --dirmode 0750 --group qemu \ >> > --daemon --pidfile /var/run/vde.pid >> > Restart=on-abort >> > >> > [Install] >> > WantedBy=multi-user.target >> > >> > Here the PID file is removed before the service is started. >> > >> > This brought up two questions. >> > - What happens is you start a service that you already started? >> Nothing, or is the service first stopped and then again started? >> >> 'systemctl start' only starts services, therefore it will do nothing if >> the service is already started. >> >> 'systemctl restart' would stop it and start it again. >> >> > - What happens if someone started the service manually? So bypassing >> systemd and running directly /usr/bin/vde_switch. >> >> As far as systemd is concerned, nothing happens - the manually started >> vde_switch is just another process inside your login session. It will >> *not* be automatically pulled into a "service" just because the program >> name or something happens to match... > > > I should learn to ask my questions better. T_T > > What I mend to ask. Someone starts /usr/bin/vde_switch manually and after that uses systemctl to start it. > If the second vde_switch instance is configured to listen on the same sockets, etc., then... Well, it depends on the daemon itself: * most will consider this a fatal error, and exit with non-zero status, causing the systemd .service to fail as well; * but some will think that the existing socket is stale, will remove it, and happily start "on top of" the first instance. (Only happens with Unix sockets, of course; if the daemon uses TCP or tries to grab the same 'tap0' interface or such, then it can only fail.) I don't know how vde behaves. It will probably refuse to start. The best way to find out, of course, is to try systemd yourself.