As previously mentioned, I still think that we should also make maxage, and friends, unsigned int.

LGTM

Just a couple of things:

• printf formats:
  

  nut/server/upsd.c

  Lines 699 to 702 in 3d79006

  	fatalx(EXIT_FAILURE,
  	"Your system limits the maximum number of connections to %d\n"
  	"but you requested %d. The server won't start until this\n"
  	"problem is resolved.\n", ret, maxconn);

• shouldn't the following be if (certrequest < NETSSL_CERTREQ_NO || certrequest > NETSSL_CERTREQ_REQUIRE) (or, given that now certrequest is unsigned and NETSSL_CERTREQ_NO is zero, just if (certrequest > NETSSL_CERTREQ_REQUIRE)) ?
  (i.e. || instead of &&, and NETSSL_CERTREQ_REQUIRE, which is 2, instead of NETSSL_CERTREQ_REQUEST, which is 1)
  

  nut/server/netssl.c

  Lines 481 to 485 in 3d79006

  	if (certrequest < NETSSL_CERTREQ_NO &&
  	certrequest > NETSSL_CERTREQ_REQUEST) {
  	upslogx(LOG_ERR, "Invalid certificate requirement");
  	return;
  	}

• how unlikely is that sysconf(_SC_OPEN_MAX) returns a) -1 or b) a value that (as long) exceeds what can be stored in an unsigned int?
  here:
  

  nut/server/upsd.c

  Line 696 in 3d79006

  ret = sysconf(_SC_OPEN_MAX);

  
  and here:
  

  nut/server/upsd.c

  Line 1251 in 3d79006

  maxconn = sysconf(_SC_OPEN_MAX);

In light of @zykh's comments, I think the change to unsigned is hasty. As pointed out, the sysconf() call shouldn't return a negative number, but a check is not expensive.