Unbound frequent restarts

DL6ER · May 29, 2021, 6:20am

I quickly checked the dhcpcd source code. dhcpcd simply reloads its configuration on receipt of SIGHUP:

NetworkConfiguration/dhcpcd/blob/01748b315d7093f458b9379bc77f19762c721314/src/dhcpcd.c#L1446-L1453

    
      
          	case SIGHUP:
          		loginfox(sigmsg, "SIGHUP", "rebinding");
          		reload_config(ctx);
          		/* Preserve any options passed on the commandline
          		 * when we were started. */
          		reconf_reboot(ctx, 1, ctx->argc, ctx->argv,
          		    ctx->argc - ctx->ifc);
          		return;

It does not send any signals to any non-dhcpcd processes so it is a "victim" of the same underlying issue.

Summary:
The cause seems to be a network device update (address change). The process causing it does not exist when manually calling ps so it is either short-lived or exited already. It may be (a) a terminating network process that fires this signal or (b) an intermediate process only existing for a few moments or (c) it is the new network process but the SIGHUP is fired before the process changed its PID by forking, etc.

To address

(a): Try setting up a small job that stores the content of ps every few minutes. This will be your memory for later checking if this PID every existed (for long enough time).
(b): I don't think this can be addressed easily.
(c): Try to find a process whose PID is the PID you are looking for +1 and +2 (look for 124 and 125 when the PID of the SIGHUP-sender is 123). This process may be unrelated but if it is always the same one, we should take a closer look here.