ntp(network time protocol) 서버 구축

설치환경

$ cat /etc/redhat-release
CentOS Linux release 7.9.2009 (Core)

설치

$ yum -y install ntp
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirror.kakao.com
 * extras: mirror.kakao.com
 * updates: mirror.navercorp.com
Resolving Dependencies
--> Running transaction check
---> Package ntp.x86_64 0:4.2.6p5-29.el7.centos.2 will be installed
--> Processing Dependency: ntpdate = 4.2.6p5-29.el7.centos.2 for package: ntp-4.                                                                                                            2.6p5-29.el7.centos.2.x86_64
--> Processing Dependency: libopts.so.25()(64bit) for package: ntp-4.2.6p5-29.el                                                                                                            7.centos.2.x86_64
--> Running transaction check
---> Package autogen-libopts.x86_64 0:5.18-5.el7 will be installed
---> Package ntpdate.x86_64 0:4.2.6p5-29.el7.centos.2 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

================================================================================
 Package              Arch        Version                       Repository
                                                                           Size
================================================================================
Installing:
 ntp                  x86_64      4.2.6p5-29.el7.centos.2       base      549 k
Installing for dependencies:
 autogen-libopts      x86_64      5.18-5.el7                    base       66 k
 ntpdate              x86_64      4.2.6p5-29.el7.centos.2       base       87 k

Transaction Summary
================================================================================
Install  1 Package (+2 Dependent packages)

Total download size: 701 k
Installed size: 1.6 M
Downloading packages:
(1/3): ntpdate-4.2.6p5-29.el7.centos.2.x86_64.rpm          |  87 kB   00:00
(2/3): ntp-4.2.6p5-29.el7.centos.2.x86_64.rpm              | 549 kB   00:00
(3/3): autogen-libopts-5.18-5.el7.x86_64.rpm               |  66 kB   00:00
--------------------------------------------------------------------------------
Total                                              2.1 MB/s | 701 kB  00:00
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : autogen-libopts-5.18-5.el7.x86_64                            1/3
  Installing : ntpdate-4.2.6p5-29.el7.centos.2.x86_64                       2/3
  Installing : ntp-4.2.6p5-29.el7.centos.2.x86_64                           3/3
  Verifying  : ntpdate-4.2.6p5-29.el7.centos.2.x86_64                       1/3
  Verifying  : ntp-4.2.6p5-29.el7.centos.2.x86_64                           2/3
  Verifying  : autogen-libopts-5.18-5.el7.x86_64                            3/3

Installed:
  ntp.x86_64 0:4.2.6p5-29.el7.centos.2

Dependency Installed:
  autogen-libopts.x86_64 0:5.18-5.el7  ntpdate.x86_64 0:4.2.6p5-29.el7.centos.2

Complete!

ntp상태확인

$ systemctl status ntpd
● ntpd.service - Network Time Service
   Loaded: loaded (/usr/lib/systemd/system/ntpd.service; disabled; vendor preset: disabled)
   Active: inactive (dead)

ntp설정

$ vi /etc/ntp.conf
# For more information about this file, see the man pages
# ntp.conf(5), ntp_acc(5), ntp_auth(5), ntp_clock(5), ntp_misc(5), ntp_mon(5).

driftfile /var/lib/ntp/drift

# Permit time synchronization with our time source, but do not
# permit the source to query or modify the service on this system.
restrict default nomodify notrap nopeer noquery

# Permit all access over the loopback interface.  This could
# be tightened as well, but to do so would effect some of
# the administrative functions.
restrict 127.0.0.1
restrict ::1

# Hosts on local network are less restricted.
#restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap

# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
server 0.centos.pool.ntp.org iburst
server 1.centos.pool.ntp.org iburst
server 2.centos.pool.ntp.org iburst
server 3.centos.pool.ntp.org iburst

• restric 설정은 peer 들이 본 서버로 sync 하는 것에 대한 제한을 한다.
• restrict default nomodify notrap noquery 설정은 기본으로 모든 권한을 주지 않음을 의미한다.
• restrict 127.0.0.1 설정은 127.0.0.1 즉, 서버 자신에서는 모든 권한을 가진다.

동기화설정

server time.bora.net iburst
server kr.pool.ntp.org iburst

iburst옵션은 5분 이상 차이날 경우 동기화진행


ntp 기동

$ systemctl start ntpd

$ systemctl status ntpd
● ntpd.service - Network Time Service
   Loaded: loaded (/usr/lib/systemd/system/ntpd.service; disabled; vendor preset: disabled)
   Active: active (running) since 일 2022-05-22 13:14:41 KST; 1s ago
  Process: 1577 ExecStart=/usr/sbin/ntpd -u ntp:ntp $OPTIONS (code=exited, status=0/SUCCESS)
 Main PID: 1578 (ntpd)
   CGroup: /system.slice/ntpd.service
           ├─1578 /usr/sbin/ntpd -u ntp:ntp -g
           └─1579 /usr/sbin/ntpd -u ntp:ntp -g

 5월 22 13:14:41 darksharavim ntpd[1578]: Listen normally on 2 lo 127.0.0.1 UDP 123
 5월 22 13:14:41 darksharavim ntpd[1578]: Listen normally on 3 ens33 192.168.245.129 UDP 123
 5월 22 13:14:41 darksharavim ntpd[1578]: Listen normally on 4 lo ::1 UDP 123
 5월 22 13:14:41 darksharavim ntpd[1578]: Listen normally on 5 ens33 fe80::202a:e792:dcad:bbe UDP 123
 5월 22 13:14:41 darksharavim ntpd[1578]: Listening on routing socket on fd #22 for interface updates
 5월 22 13:14:41 darksharavim ntpd[1578]: Deferring DNS for time.bora.org 1
 5월 22 13:14:41 darksharavim ntpd[1578]: 0.0.0.0 c016 06 restart
 5월 22 13:14:41 darksharavim ntpd[1578]: 0.0.0.0 c012 02 freq_set kernel 0.000 PPM
 5월 22 13:14:41 darksharavim ntpd[1578]: 0.0.0.0 c011 01 freq_not_set
 5월 22 13:14:41 darksharavim ntpd[1579]: signal_no_reset: signal 17 had flags 4000000

동기화확인

$ ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*time.bora.net   90.1.14.51       2 u   44   64  365    3.260  -11.376   9.337

* remote : sync 하고 있는 ntp server
ntp.conf 파일에 등록된 server ip가 출력되며 /etc/hosts파일에 매핑되는 hosts가 존재하면 해당 hostname으로 출력.
또한 현재 동기화 중인 NTP서버는 [ * ], secondary NTP서버는 [ + ] 로 표시됩니다.
ntp 프로세스가 기동된지 얼마 되지 않았거나, 네트워크 상의 문제로 NTP서버와 sync 되지 않을 시 [ *, +] 기호 없이 출력됩니다.

* refid : remote의 reference 주소 라는데 설명하자면 ntpserver1 이 바라보는 주소
> 현재 ntp 서버로 sycn 중인 서버가 sync중인 NTP 주소, 내부 sync면 GPS로 표시됨

* st : remote stratum (GPS = stratum 0)

* t : 시간을 받아보는 방식 (uniquest, multicast, broadcast)

* when : NTP 서버로 부터 데이터를 수신한 후 경과 시간, 초 단위 이며 수신받으면 0으로 초기화

* poll : NTP 서버에 sync 요청 주기, 초 단위

* reach : 최근 8번 poll 요청에 대한 응답 여부 - 1, 3, 7, 17, 37, 77 ,177, 377 값으로 표시될 경우 정상

* delay : Network 지연시간이며, millisecond 단위

* offset : NTP서버와 로컬(자신) 의 시간 차이, millisecond 단위

* disp : offset 에 대한 분산 (jitter)