[systemd-devel] systemd-notify --ready is not reliable

[pradip K]

Eelco Dolstra <eelco.dolstra <at> logicblox.com> writes:



> 
> Hi all,
> 
> I've noticed that the command "systemd-notify --ready" does not work
reliably to
> signal that a service is ready. It works sometimes, but most of the time
you get
> a message like:
> 
>   systemd[1]: Cannot find unit for notify message of PID 3137.
> 
> in the journal, and the service stays in the "activating" state.
> 
> The reason is that systemd-notify sends its message asynchronously and exits
> immediately. So by the time systemd processes the message, systemd-notify has
> probably already exited, and so systemd cannot gets cgroup. (Note that this
> affects other systemd-notify messages as well, but for --ready it's
particularly
> bad because it causes services to "hang" in the "activating" state.)
> 
> Any suggestions what to do about this? I can see a few solutions:
> 
> * Have sd_notify() include its own unit name in the notification message. This
> would be insecure (though probably fine if the sender is root). However, it
> could be made secure by having systemd pass some random cookie to services via
> an environment variable, which sd_notify() could then include in its
> notification messages to authenticate itself.
> 
> * Make systemd-notify synchronous, i.e., have it wait for a message back from
> systemd after it has determined the client's unit. Not entirely trivial given
> that sd_notify() uses SOCK_DGRAM.
> 
> * Give each service its own notification socket, rather than using the global
> /run/systemd/notify. That is, in the service, set $NOTIFY_SOCKET to something
> like /run/systemd/notify-foo.service, and have systemd listen on that
socket. By
> making the socket private to the service's mount namespace, you would know for
> sure that any message arriving on the socket comes from the service.
> 
> * Document that you shouldn't use systemd-notify. Not an ideal solution 
> 
> What do you think?
> 

Hi Eelco,

Ref: http://permalink.gmane.org/gmane.comp.sysutils.systemd.devel/18649

I am trying implement watchdog feature using sd_notify, could you pls give
us more details on setting $NOTIFY_SOCKET.
Like how to create socket and assign to environment NOTIFY_SOCKET for this 


[Unit]
After=snmpd.service
Before=exxxl.service nxx.service ixx.service lac

[Service]
Type=notify
ExecStart=/data/ABC -d
ExecStop=/data/pkill ABC
TimeoutStopSec=5
Environment=NOTIFY_SOCKET=
WatchdogSec=30s
NotifyAccess=all
FailureAction==reboot-force

[Install]
WantedBy=multi-user.target 

Best regards,
Pradip.