Here's the 3rd installment of my series of posts highlighting key new features of the upcoming v256 release of systemd.
You might have heard of the sd_notify() protocol that services running on systemd can use to notify the service manager about status changes, in particular about service readiness. systemd uses that to synchronize start, reload and stop operations between daemon code and service manager (as well as a multitude of other things).
But did you know that the service manager itself also sends out sd_notify() messages to let whatever started it know about its own status changes?
How is that useful you wonder? When systemd runs in a container, a container manager can use this to determine when precisely the container is ready and connectible. When systemd is running in the per-user instance, then the per-system instance can know this way when it fully started up. Finally, since v253 the interface supports AF_VSOCK…
@pid_eins thoughts on supporting inet sockets? So that this mechanism can be extended to clusters, instead of just vms?
@hsaliak unlike af_unix and af_vsock, af_inet is unreliable, needs encryption/authentication and so on, comes available only during late boot, typically after dhcp and so on, and hence is a very very different beast.
@pid_eins I expected that to be the reason. Thanks for clarifying