Instrumentation for metrics

Craig Miskell cmiskell at
Wed Jan 22 09:10:18 AEDT 2020

On 21/01/20 8:44 pm, Damien Miller wrote:
 > On Tue, 21 Jan 2020, Philipp Marek wrote:
 >>> This makes me think that the syslog approach is probably the way to go
 >> Yeah, right.
 >> Another idea is to mirror the current preauth load via setproctitle()...
 >> That makes that data accessible even without a syscall (at least the
 >> writing of the data - quering needs syscalls, right), so that can be
 >> kept up-to-date and allows a high monitoring frequency as well.
 >> Multiple instances of SSHd (on different ports) are easily distinguished
 >> as well.
 > That's a really, really good idea. Patch below.

That would certainly cover my use case.  I wonder if there's a case to 
be made to add options.max_startups_begin to the title status (per the 
amended patch below).  It's more informative, but also a bit more 
confusing e.g. when we're above max_startups_begin and beginning to drop 
we get a title like:

sshd: [listener] 12/10/100 startups

But my primary goal here is getting that first number exposed and we 
could reasonably make max_startups_begin and max_startups the same; for 
us, once we start dropping any we may as well be dropping them all, 
because it happening at all is a thing to be avoided, and we want 
to/should have been alerted before it happens.  So the original patch 
would certainly be sufficient.

Just an aside: I notice that the original patch got included in commit 
f8c11461aa6db168fc5e7eeae448b4cbbf59642a in the portable git repo, along 
with another change that matches the commit message.  Was that intentional?

-- Craig Miskell Site Reliability Engineer | GitLab | Dunedin, New Zealand

diff --git a/sshd.c b/sshd.c
index 6129b0a..debbdcb 100644
--- a/sshd.c
+++ b/sshd.c
@@ -1005,7 +1005,7 @@ server_accept_loop(int *sock_in, int *sock_out, 
int *newsock, int *config_s)
  	fd_set *fdset;
  	int i, j, ret, maxfd;
-	int startups = 0, listening = 0, lameduck = 0;
+	int ostartups = -1, startups = 0, listening = 0, lameduck = 0;
  	int startup_p[2] = { -1 , -1 };
  	char c = 0;
  	struct sockaddr_storage from;
@@ -1029,6 +1029,11 @@ server_accept_loop(int *sock_in, int *sock_out, 
int *newsock, int *config_s)
  	 * the daemon is killed with a signal.
  	for (;;) {
+		if (ostartups != startups) {
+			setproctitle("[listener] %d/%d/%d startups",
+			    startups, options.max_startups_begin, options.max_startups);
+			ostartups = startups;
+		}
  		if (received_sighup) {
  			if (!lameduck) {
  				debug("Received SIGHUP; waiting for children");

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