On Mon, Sep 03, 2018 at 10:48:27PM +0000, Debian Bug Tracking System wrote:
> Subject: ntpdc times out when the server monlist has over 600 clients
>
> Apparently the people at support.ntp.org have it documented:
>
> http://support.ntp.org/bin/view/Support/MonitoringAndControllingNTP#Who_is_using_my_NTP_server
>
> | Please note that a maximum of 600 entries is supported with current
> | versions of ntpdc. The protocol (or better: the contents of the return
> | packets) used by ntpdc is not standardized, therefore it is recommended
> | to only use ntpdc with a matching ntpd, i.e. both should have the same
> | version number.
> |
> | To get by this 600 entry limitation, many server operators run client
> | statistics scripts [...]
>
> I went to look at the code, and it looks like ntpdc/ntpdc.c is printing the
> contents of the haveseq array, whose size is MAXSEQ+1, which would be 128,
> so that doesn't sound like. At the other end,
> ntpd/ntp_request.c:mon_getlist_0() is sending over all of the mon_data
> structures found in mon_mru_list, and after looking at that, I see the
> culprit in ntpd/ntp_monitor.c:
>
> /*
> * Limits on the number of structures allocated. This limit is picked
> * with the illicit knowlege that we can only return somewhat less
> * than 8K bytes in a mode 7 response packet, and that each structure
> * will require about 20 bytes of space in the response.
> *
> * ... I don't believe the above is true anymore ... jdg
> */
> #ifndef MAXMONMEM
> #define MAXMONMEM 600 /* we allocate up to 600 structures */
> #endif
> [...]
> int
> ntp_monitor(
> [...]
> if (mon_free == NULL && mon_total_mem >= MAXMONMEM) {
> [...]
>
> I can't help but think that there are better ways to handle this in
> both ntpd and ntpdc. :)
I looked this up after getting the closure message, and it looks like it
might have been addressed upstream with:
commit 9407fc0ef596404e620317a0acf39d63ed27c550
Author: <davehart@[...]>
Date: Sat Feb 27 08:47:04 2010 +0000
[...]
Many files:
add MRU sizing knobs:
mru mindepth 600 maxage 64 maxdepth 1024 maxmem 4096
entries beyond 600 which are older than 64s are reclaimed,
with a hard upper limit on the size of maxdepth (indirectly
set by maxmem).
[...]
--
2. That which causes joy or happiness.
