Changes between Version 4 and Version 5 of ntp

Timestamp:

06/16/2017 07:36:10 PM (8 years ago)

Author:

ken@…

Comment:

Rework how to fix ntpd failing to sync - problem now attributed to suspend to RAM.

ntp

@@ -45 +45 @@
 }}}
 
-== Fixes if synchronisation fails ==
+== Fixes if synchronisation fails following frequent suspend to RAM ==
 
-For a long time the default kernel clocksource has been tsc, but it used to be acpi_pm. On one of my machines, in one kernel release, I lost synchronisation and the log showed:
+On one of my machines, ntp had lost synchronisation. I initially blamed the tsc clocksource in a particular kernel version, and recommended changing it back to acpi_pm.
+
+=== From the initial version of this section: ===
+
+On one of my machines, in one kernel release, I lost synchronisation and the log showed:
 {{{
 frequency error 1726 PPM exceeds tolerance 500 PPM
@@ -66 +70 @@
 to the bootargs in grub.
 
+=== A better fix (sysvinit) ===
+
+I forgot about the problem, until one day when I discovered that my desktop clock was 5 minutes slow. In the end, this appears to be related to frequent suspend to RAM, sometimes for a few days. In early versions of pm-utils (which is what I use for s2ram) there was a script to fix up ntpd - but that was removed long ago, in the belief that the clock would only drift for a maximum of 64 seconds realtime (not drift *by* 64 seconds!) and then ntpd would start to sync it. For systemd the preferred methods are apparently different. Anyway,I've now added the following script as  /usr/lib/pm-utils/sleep.d/48ntpd (mode 755) and things seem to work - using 'ntpq -p' I can sometimes see offsets of several hundred milliseconds (and increasing!) even when the box has sync'd to my local server, but it seems to stay accurate to within a second, and eventually syncs to a few milliseconds.
+
+
+{{{
+#!/bin/sh
+# stop ntpd on suspend, fix and start fresh on wakeup
+
+. "${PM_FUNCTIONS}"
+
+case $1 in
+    suspend)
+        /etc/rc.d/init.d/ntpd stop
+        ;;
+    resume)
+        /usr/sbin/ntpd -gq
+        /etc/rc.d/init.d/ntpd start
+    *) exit 0 ;;
+esac
+exit 0
+}}}
+
+
 == When the clock is too far away from the correct time ==
 
-If ntpd bails out because the clock is too far from the correct time, try stopping ntpd, using
+If ntpd bails out because the clock is too far from the correct time, try stopping ntpd, then use
 {{{
 ntpd -gq
 }}}
-to let it sync, and then restarting ntpd. According to the man page, -g can be used multiple times if the clock is far adrift.
+to let it sync, and then restart ntpd. According to the man page, -g can be used multiple times if the clock is far adrift.