Alternatively, you can install the new Chrony service that is quicker to synchronize clocks in mobile and virtual systems.<\/p>\n
Install the Chrony service:
\n# yum install -y chrony<\/p>\n
Activate the Chrony service at boot:
\n# systemctl enable chronyd<\/p>\n
Start the Chrony service:
\n# systemctl start chronyd<\/p>\n
[root@apache2 ~]# yum install chrony -y
\nLoaded plugins: fastestmirror
\nLoading mirror speeds from cached hostfile
\n * base: mirror.vodien.com
\n * extras: mirror.vodien.com
\n * updates: mirror.vodien.com
\nPackage chrony-2.1.1-1.el7.centos.x86_64 already installed and latest version
\nNothing to do
\n[root@apache2 ~]# systemctl start crond.service
\n[root@apache2 ~]#
\n[root@apache2 ~]#
\n[root@apache2 ~]#
\n[root@apache2 ~]#
\n[root@apache2 ~]# systemctl status crond.service
\n? crond.service – Command Scheduler
\n Loaded: loaded (\/usr\/lib\/systemd\/system\/crond.service; enabled; vendor preset: enabled)
\n Active: active (running) since Sat 2016-05-14 20:13:14 SGT; 1h 48min ago
\n Main PID: 848 (crond)
\n CGroup: \/system.slice\/crond.service
\n ??848 \/usr\/sbin\/crond -n<\/p>\n
May 14 20:13:14 apache2.rmohan.com systemd[1]: Started Command Scheduler.
\nMay 14 20:13:14 apache2.rmohan.com systemd[1]: Starting Command Scheduler…
\nMay 14 20:13:14 apache2.rmohan.com crond[848]: (CRON) INFO (RANDOM_DELAY will be scaled with factor 57% if used.)
\nMay 14 20:13:14 apache2.rmohan.com crond[848]: (CRON) INFO (running with inotify support)
\nMay 14 22:00:15 apache2.rmohan.com systemd[1]: Started Command Scheduler.
\n[root@apache2 ~]# systemctl enable crond.service
\n[root@apache2 ~]# chr
\nchronyc chronyd chroot chrt
\n[root@apache2 ~]# chronyd
\n[root@apache2 ~]# chrony
\nchronyc chronyd
\n[root@apache2 ~]# chronyc
\nchrony version 2.1.1
\nCopyright (C) 1997-2003, 2007, 2009-2015 Richard P. Curnow and others
\nchrony comes with ABSOLUTELY NO WARRANTY. This is free software, and
\nyou are welcome to redistribute it under certain conditions. See the
\nGNU General Public License version 2 for details.<\/p>\n
chronyc> quit<\/p>\n
The Chrony configuration is in the \/etc\/chrony.conf file:<\/p>\n
[root@apache2 ~]# cat \/etc\/chrony.conf
\n# Use public servers from the pool.ntp.org project.
\n# Please consider joining the pool (http:\/\/www.pool.ntp.org\/join.html).
\nserver 0.centos.pool.ntp.org iburst
\nserver 1.centos.pool.ntp.org iburst
\nserver 2.centos.pool.ntp.org iburst
\nserver 3.centos.pool.ntp.org iburst<\/p>\n
# Ignore stratum in source selection.
\nstratumweight 0<\/p>\n
# Record the rate at which the system clock gains\/losses time.
\ndriftfile \/var\/lib\/chrony\/drift<\/p>\n
# Enable kernel RTC synchronization.
\nrtcsync<\/p>\n
# In first three updates step the system clock instead of slew
\n# if the adjustment is larger than 10 seconds.
\nmakestep 10 3<\/p>\n
# Allow NTP client access from local network.
\n#allow 192.168\/16<\/p>\n
# Listen for commands only on localhost.
\nbindcmdaddress 127.0.0.1
\nbindcmdaddress ::1<\/p>\n
# Serve time even if not synchronized to any NTP server.
\n#local stratum 10<\/p>\n
keyfile \/etc\/chrony.keys<\/p>\n
# Specify the key used as password for chronyc.
\ncommandkey 1<\/p>\n
# Generate command key if missing.
\ngeneratecommandkey<\/p>\n
# Disable logging of client accesses.
\nnoclientlog<\/p>\n
# Send a message to syslog if a clock adjustment is larger than 0.5 seconds.
\nlogchange 0.5<\/p>\n
logdir \/var\/log\/chrony
\n#log measurements statistics tracking
\n[root@apache2 ~]#<\/p>\n
Note: For basic configuration purpose, only the server directives could need a change to point at a different set of master time servers than the defaults specified.<\/p>\n
To get information about the main time reference, type:<\/p>\n
#log measurements statistics tracking
\n[root@apache2 ~]# chronyc tracking
\nReference ID : 202.156.0.34 (time2.maxonline.com.sg)
\nStratum : 2
\nRef time (UTC) : Sat May 14 04:01:50 2016
\nSystem time : 0.001108132 seconds fast of NTP time
\nLast offset : +0.002678378 seconds
\nRMS offset : 0.002678378 seconds
\nFrequency : 37.078 ppm fast
\nResidual freq : +0.000 ppm
\nSkew : 315.347 ppm
\nRoot delay : 0.015427 seconds
\nRoot dispersion : 0.011265 seconds
\nUpdate interval : 64.9 seconds
\nLeap status : Normal
\n[root@apache2 ~]#<\/p>\n
To get equivalent information to the ntpq command, type:
\n[root@apache2 ~]# chronyc sources -v
\n210 Number of sources = 4<\/p>\n
.– Source mode ‘^’ = server, ‘=’ = peer, ‘#’ = local clock.
\n \/ .- Source state ‘*’ = current synced, ‘+’ = combined , ‘-‘ = not combined,
\n| \/ ‘?’ = unreachable, ‘x’ = time may be in error, ‘~’ = time too variable.
\n|| .- xxxx [ yyyy ] +\/- zzzz
\n|| Reachability register (octal) -. | xxxx = adjusted offset,
\n|| Log2(Polling interval) –. | | yyyy = measured offset,
\n|| \\ | | zzzz = estimated error.
\n|| | | \\
\nMS Name\/IP address Stratum Poll Reach LastRx Last sample
\n===============================================================================
\n^- shim.active-apps.net 2 6 37 58 +14ms[ +14ms] +\/- 61ms
\n^- time1.maxonline.com.sg 1 6 77 64 -2046us[-2046us] +\/- 3682us
\n^* time2.maxonline.com.sg 1 6 77 4 -1368us[-6926us] +\/- 4931us
\n^- tor-exit.katzen.me 2 6 77 9 +4244us[+4244us] +\/- 49ms<\/p>\n
Time synchronization can also be forced with the below chronyc commands.<\/p>\n
[root@apache2 ~]# chronyc -a ‘burst 4\/4’
\n200 OK
\n200 OK
\n[root@apache2 ~]# chronyc -a makestep
\n200 OK
\n200 OK
\n[root@apache2 ~]#<\/p>\n
Chronyc can also be used to view detailed NTP specific information as demonstrated below.
\n[root@apache2 ~]# chronyc tracking
\nReference ID : 202.156.0.34 (time2.maxonline.com.sg)
\nStratum : 2
\nRef time (UTC) : Sat May 14 04:08:53 2016
\nSystem time : 0.000000000 seconds slow of NTP time
\nLast offset : -0.000051153 seconds
\nRMS offset : 0.001930560 seconds
\nFrequency : 2.401 ppm slow
\nResidual freq : -0.003 ppm
\nSkew : 2.714 ppm
\nRoot delay : 0.006534 seconds
\nRoot dispersion : 0.000577 seconds
\nUpdate interval : 2.1 seconds
\nLeap status : Normal
\n[root@apache2 ~]# date
\nSat May 14 12:09:54 SGT 2016<\/p>\n
We can also view all NTP servers that chronyc is synchronizing with.
\n[root@apache1 ~]# chronyc sources
\n210 Number of sources = 4
\nMS Name\/IP address Stratum Poll Reach LastRx Last sample
\n===============================================================================
\n^+ 103.224.117.98 4 6 17 26 -5985us[-6099us] +\/- 135ms
\n^+ frontier.innolan.net 2 6 17 26 +2607us[+2478us] +\/- 71ms
\n^* tor-exit.katzen.me 2 6 17 25 -499us[ -644us] +\/- 57ms
\n^- gandhari.thirdeye.it 2 6 17 25 +3135us[+3135us] +\/- 364ms
\n[root@apache1 ~]# chronyc -a ‘burst 4\/4’<\/p>\n
Further information on these sources can then be viewed.
\n[root@centos7 ~]# chronyc sourcestats<\/p>\n
[root@apache2 ~]# chronyc sourcestats
\n210 Number of sources = 4
\nName\/IP Address NP NR Span Frequency Freq Skew Offset Std Dev
\n==============================================================================
\nshim.active-apps.net 18 9 689 +1.049 15.882 +2220us 4358us
\ntime1.maxonline.com.sg 12 6 618 +0.582 4.374 +164us 648us
\ntime2.maxonline.com.sg 16 14 624 -0.487 2.781 -185us 563us
\ntor-exit.katzen.me 12 7 617 -0.846 9.713 +4003us 1389us
\n[root@apache2 ~]#<\/p>\n","protected":false},"excerpt":{"rendered":"
Alternatively, you can install the new Chrony service that is quicker to synchronize clocks in mobile and virtual systems.<\/p>\n
Install the Chrony service: # yum install -y chrony<\/p>\n
Activate the Chrony service at boot: # systemctl enable chronyd<\/p>\n
Start the Chrony service: # systemctl start chronyd<\/p>\n
[root@apache2 ~]# yum install chrony -y Loaded plugins: fastestmirror […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[73],"tags":[],"_links":{"self":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/5932"}],"collection":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5932"}],"version-history":[{"count":2,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/5932\/revisions"}],"predecessor-version":[{"id":5934,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/5932\/revisions\/5934"}],"wp:attachment":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5932"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5932"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5932"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}