在配置hadoop集群时，时间同步是必须要做的，否则会出现各种意想不到的问题。
hadoop102 为 ntp server，hadoop103以及hadoop104 为ntp client（即需要同步时间机器）
1.全部机器都要安装ntp以及ntpdate
sudo apt-get install ntp
sudo apt-get install ntpdate
2.关闭所有的机器的ntp,每个机器执行命令 一下命令
sudo service ntp stop
查看ntp状态
sudo service ntp status
3.修改ntp server即hadoop102的/etc/ntp.conf文件
sudo vim /etc/ntp.conf
相关条文解释，参考https://www.cnblogs.com/xwdreamer/p/3448773.html
# /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help driftfile /var/lib/ntp/ntp.drift # Leap seconds definition provided by tzdata leapfile /usr/share/zoneinfo/leap-seconds.list # Enable this if you want statistics to be logged. #statsdir /var/log/ntpstats/ statistics loopstats peerstats clockstats filegen loopstats file loopstats type day enable filegen peerstats file peerstats type day enable filegen clockstats file clockstats type day enable # Specify one or more NTP servers. # Use servers from the NTP Pool Project. Approved by Ubuntu Technical Board # on 2011-02-08 (LP: #104525). See http://www.pool.ntp.org/join.html for # more information. pool 0.ubuntu.pool.ntp.org iburst pool 1.ubuntu.pool.ntp.org iburst pool 2.ubuntu.pool.ntp.org iburst pool 3.ubuntu.pool.ntp.org iburst # Use Ubuntu‘s ntp server as a fallback. pool ntp.ubuntu.com # Access control configuration; see /usr/share/doc/ntp-doc/html/accopt.html for # details. The web page <http://support.ntp.org/bin/view/Support/AccessRestrictions> # might also be helpful. # # Note that "restrict" applies to both servers and clients, so a configuration # that might be intended to block requests from certain clients could also end # up blocking replies from your own upstream servers. # By default, exchange time with everybody, but don‘t allow configuration. restrict -4 default kod notrap nomodify nopeer noquery limited restrict -6 default kod notrap nomodify nopeer noquery limited # Local users may interrogate the ntp server more closely. restrict 127.0.0.1 restrict ::1 # Needed for adding pool entries restrict source notrap nomodify noquery # Clients from this (example!) subnet have unlimited access, but only if # cryptographically authenticated. #restrict 192.168.123.0 mask 255.255.255.0 notrust # If you want to provide time to your local subnet, change the next line. # (Again, the address is an example only.) #broadcast 192.168.123.255 # If you want to listen to time broadcasts on your local subnet, de-comment the # next lines. Please do this only if you trust everybody on the network! #disable auth #broadcastclient
改为如下后保存：
# /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help
driftfile /var/lib/ntp/ntp.drift
# Leap seconds definition provided by tzdata
leapfile /usr/share/zoneinfo/leap-seconds.list
# Enable this if you want statistics to be logged.
#statsdir /var/log/ntpstats/
statistics loopstats peerstats clockstats
filegen loopstats file loopstats type day enable
filegen peerstats file peerstats type day enable
filegen clockstats file clockstats type day enable
# Use servers from the NTP Pool Project. Approved by Ubuntu Technical Board # on 2011-02-08 (LP: #104525). See http://www.pool.ntp.org/join.html for # more information. #pool 0.ubuntu.pool.ntp.org iburst #pool 1.ubuntu.pool.ntp.org iburst #pool 2.ubuntu.pool.ntp.org iburst #pool 3.ubuntu.pool.ntp.org iburst # Use Ubuntu‘s ntp server as a fallback. #pool ntp.ubuntu.com server 127.127.1.0 fudge 127.127.1.0 stratum 10 # Access control configuration; see /usr/share/doc/ntp-doc/html/accopt.html for # details. The web page <http://support.ntp.org/bin/view/Support/AccessRestrictions> # might also be helpful. # # Note that "restrict" applies to both servers and clients, so a configuration # that might be intended to block requests from certain clients could also end # up blocking replies from your own upstream servers. # By default, exchange time with everybody, but don‘t allow configuration. restrict -4 default kod notrap nomodify nopeer noquery limited restrict -6 default kod notrap nomodify nopeer noquery limited # Local users may interrogate the ntp server more closely. restrict 127.0.0.1 restrict ::1 # Needed for adding pool entries restrict source notrap nomodify noquery # Clients from this (example!) subnet have unlimited access, but only if # cryptographically authenticated. restrict 192.168.123.0 mask 255.255.255.0 nomodify notrap # If you want to provide time to your local subnet, change the next line. # (Again, the address is an example only.) #broadcast 192.168.123.255
4.对ntp server （hadoop102）执行命令，开启服务
sudo service ntp start
5.同步时间(除hadoop102的其他机器都要执行)
sudo ntpdate hadoop102
6 在除hadoop102的其他机器，将同步时间的命令放在crontab中(切换到root用户下操作)
*/10 * * * * /usr/sbin/ntpdate hadoop102
每十分钟更新一次
相关错误：
no server suitable for synchronization found
http://www.blogjava.net/spray/archive/2008/07/10/213964.html
Ubuntu 时间设置
https://www.cnblogs.com/qiumingcheng/p/12210629.html