Linux Configuration files
restrict default notrap restrict 127.0.0.1 server 10.165.112.1 server 127.127.1.0 # local clock fudge 127.127.1.0 stratum 10 driftfile /var/lib/ntp/drift broadcastdelay 0.008 keys /etc/ntp/keys
# Drop root to id 'ntp:ntp' by default. OPTIONS="-x -u ntp:ntp -p /var/run/ntpd.pid" # Set to 'yes' to sync hw clock after successful ntpdate SYNC_HWCLOCK=yes
For RAC implement NTP with slewing option ( -x )
Applicable to platforms: All Linux and Unix Platforms.
Why?: Without the slew option NTP will shift the system clock forwards or backwards when the time discrepancy exceeds a specific (platform dependent) threshold. Large backward time shifts can result in the Clusterware thinking that checkins have been missed resulting in node evictions. For this reason it is highly recommended that NTP be configured to slew time (speed up or slow down) the clock to synchronize the time to prevent such evictions. For more information on how to implement NTP time slewing on your platform please refer to the Platform Specific RAC and Oracle Clusterware Best Practice and Starter Kit Notes (see below).
Start and stop NTP service
On CentOS/RHEL/Fedora: $ service ntpd start $ chkconfig ntpd on $ service ntpd stop # /etc/init.d/ntpd stop Shutting down ntpd: [ OK ] # /etc/init.d/ntpd start Starting ntpd: [ OK ]
Synchronize time with a known ntp server using ntpdate
# ntpdate -u 10.165.112.1 27 May 12:46:52 ntpdate: adjust time server 10.165.112.1 offset 0.420523 sec
Query all NTP servers defined in /etc/ntp.conf
# ntpq -p remote refid st t when poll reach delay offset jitter =============== ============================================================== nurnberg-rtr-1- 22.214.171.124 3 u 7 64 1 1.204 506.456 0.031 LOCAL(0) .LOCL. 10 l 4 64 1 0.000 0.000 0.031
Doing An Initial Synchronization
The ntpdate command runs three times to synchronize clock, but it must be run while the ntpd
process is stopped. So you’ll have to stop ntpd, run ntpdate and then start ntpd again.
Initial settings: # ntpq -p remote refid st t when poll reach delay offset jitter ============================================================================== nurnberg-rtr-1- 126.96.36.199 3 u 87 128 377 0.964 -198.53 8951.67 *LOCAL(0) .LOCL. 10 l 20 64 377 0.000 0.000 0.000 Stop NTPD service: # service ntpd stop Shutting down ntpd: [ OK ] Run ntpdate: # ntpdate -u 10.165.112.1 1 Jun 17:24:04 ntpdate: adjust time server 10.165.112.1 offset -0.244832 sec Restart NTPD service: # service ntpd start Starting ntpd: [ OK ] Confirm time sycronization: # ntpq -p remote refid st t when poll reach delay offset jitter ============================================================================== nurnberg-rtr-1- 188.8.131.52 3 u 4 64 1 1.000 -240.43 5.110 LOCAL(0) .LOCL. 10 l 3 64 1 0.000 0.000 0.000 --> Times server is polled every 64 seconds - last polled issued 4 seconds ago the current time difference is 240 ms - the difference between last 2 runs is 5.11 ms Parameters: remote: The remote peer or server being synced to. “LOCAL” is this local host (included in case there are no remote peers or servers available); refid: Where or what the remote peer or server is itself synchronised to; st : The remote peer or server Stratum t: Type (u: unicast or manycast client, b: broadcast or multicast client, l: local reference clock, s: symmetric peer, A: manycast server, B: broadcast server, M: multicast server, see “Automatic Server Discovery“); when: number of seconds passed since last response poll: polling interval, in seconds, for source reach: indicates success/failure to reach source, 377 all attempts successful delay: indicates the roundtrip time, in milliseconds, to receive a reply offset: indicates the time difference, in milliseconds, between the client server and source disp/jitter: indicates the difference, in milliseconds, between two samples
Add the following lines to rc.local to syncronize date on every VirtualBox reboot
# # stop service to all ntpdate to work # service ntpd stop ntpdate -u 10.165.112.1 service ntpd start