====== NTP: ======

==== Config file: ====
/etc/ntp.conf

==== timedatectl: ====
Gives information on time, date and timezone:
<code>
timedatectl
Local time: Sun 2021-11-21 11:57:23 CET
           Universal time: Sun 2021-11-21 10:57:23 UTC
                 RTC time: Sun 2021-11-21 10:57:23
                Time zone: Europe/Amsterdam (CET, +0100)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no
</code>

<code>
timedatectl --help

status                   Show current time settings
show                     Show properties of systemd-timedated
set-time TIME            Set system time
set-timezone ZONE        Set system time zone
list-timezones           Show known time zones
set-local-rtc BOOL       Control whether RTC is in local time
set-ntp BOOL             Enable or disable network time synchronization

systemd-timesyncd Commands:
timesync-status          Show status of systemd-timesyncd
show-timesync            Show properties of systemd-timesyncd
</code>


==== Voorbeeld van ntp.conf: ====

<code>
## Use 'server' for a real NTP server and use 'pool' for
## a pool of servers if the ntp version supports it,
## otherwise define multiple server lines (See: www.pool.ntp.org/en/use.html)
## Added 'iburst' to speed up the initial synchronization.
server          172.17.9.58 iburst
## Multiple server configuration is possible:
server          ntp-time.for.mydomain
server          otherntp.server.org
server          ntp.research.gov 	

driftfile       /var/lib/ntp/drift/ntp.drift
logfile         /var/log/ntp

## Key file containing the keys and key identifiers used when operating
## with symmetric key cryptography - disabled
#keys           /etc/ntp.keys

## Specify the key identifiers which are trusted.
trustedkey      1

## Specify the key identifier to use with the ntpdc utility.
requestkey      1

## mitigate CVE-2013-5211 in case we are running a version before 4.2.7p26
## N/A for SLES12SP3 GA
#disable                monitor

## Permit time synchronization with our time source, but do not
## permit the source to query or modify the service on this system.
restrict        default         kod limited nomodify notrap nopeer noquery
restrict -6     default         kod limited 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 -6     ::1
</code>

==== Om handmatig een sync te doen: ====

<code>
ntpdate -u 10.126.33.101

output: 29 Jun 09:45:03 ntpdate[1649]: step time server 10.126.33.101 offset 126.149871 sec
</code>

==== Apply changes: ====
<code>
service ntpd start 

or

systemctl start ntpd
</code>