Specify a Remote NTP Server

An XCCDF Rule

Description

Depending on specific functional requirements of a concrete production environment, the Red Hat Enterprise Linux 7 system can be configured to utilize the services of the chronyd NTP daemon (the default), or services of the ntpd NTP daemon. Refer to https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/system_administrators_guide/ch-configuring_ntp_using_the_chrony_suite for more detailed comparison of the features of both of the choices, and for further guidance how to choose between the two NTP daemons.
To specify a remote NTP server for time synchronization, perform the following:

if the system is configured to use the chronyd as the NTP daemon (the default), edit the file /etc/chrony.conf as follows,
if the system is configured to use the ntpd as the NTP daemon, edit the file /etc/ntp.conf as documented below.

Add or correct the following lines, substituting the IP or hostname of a remote NTP server for ntpserver:

server ntpserver

This instructs the NTP software to contact that remote server to obtain time data.

Rationale

Synchronizing with an NTP server makes it possible to collate system logs from multiple sources or correlate computer events with real time events.

ID: xccdf_org.ssgproject.content_rule_chronyd_or_ntpd_specify_remote_server
Severity: Medium
References: 1 14 15 16 3 5 6

APO11.04 BAI03.05 DSS05.04 DSS05.07 MEA02.01

3.3.7

CCI-000160 CCI-001891

4.3.3.3.9 4.3.3.5.8 4.3.4.4.7 4.4.2.1 4.4.2.2 4.4.2.4

SR 2.10 SR 2.11 SR 2.12 SR 2.8 SR 2.9

A.12.4.1 A.12.4.2 A.12.4.3 A.12.4.4 A.12.7.1

AU-12(1) AU-8(1)(a) AU-8(2) CM-6(a)

PR.PT-1

Req-10.4.1 Req-10.4.3

CCE-27278-1

SRG-APP-000116-CTR-000235
Updated: about 1 year ago

# Remediation is applicable only in certain platforms
if [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ] && { ( [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ] && ( rpm --quiet -q chrony || rpm --quiet -q ntp ) ); }; then

var_multiple_time_servers='<xccdf-1.2:sub xmlns:xccdf-1.2="http://checklists.nist.gov/xccdf/1.2" idref="xccdf_org.ssgproject.content_value_var_multiple_time_servers" use="legacy"/>'

config_file="/etc/ntp.conf"
/usr/sbin/pidof ntpd || config_file="/etc/chrony.conf"

if ! grep -q ^server "$config_file" ; then
  if ! grep -q '#[[:space:]]*server' "$config_file" ; then
    for server in $(echo "$var_multiple_time_servers" | tr ',' '\n') ; do
      printf '\nserver %s' "$server" >> "$config_file"
    done
  else
    sed -i 's/#[ \t]*server/server/g' "$config_file"
  fi
fi

else
    >&2 echo 'Remediation is not applicable, nothing was done'
fi

---
apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
spec:
  config:
    ignition:      version: 3.1.0
    storage:
      files:
      - contents:
          source: data:,{{ %23%20Allow%20for%20extra%20configuration%20files.%20This%20is%20useful%0A%23%20for%20admins%20specifying%20their%20own%20NTP%20servers%0Ainclude%20/etc/chrony.d/%2A.conf%0A%0A%23%20Set%20chronyd%20as%20client-only.%0Aport%200%0A%0A%23%20Disable%20chronyc%20from%20the%20network%0Acmdport%200%0A%0A%23%20Record%20the%20rate%20at%20which%20the%20system%20clock%20gains/losses%20time.%0Adriftfile%20/var/lib/chrony/drift%0A%0A%23%20Allow%20the%20system%20clock%20to%20be%20stepped%20in%20the%20first%20three%20updates%0A%23%20if%20its%20offset%20is%20larger%20than%201%20second.%0Amakestep%201.0%203%0A%0A%23%20Enable%20kernel%20synchronization%20of%20the%20real-time%20clock%20%28RTC%29.%0Artcsync%0A%0A%23%20Enable%20hardware%20timestamping%20on%20all%20interfaces%20that%20support%20it.%0A%23hwtimestamp%20%2A%0A%0A%23%20Increase%20the%20minimum%20number%20of%20selectable%20sources%20required%20to%20adjust%0A%23%20the%20system%20clock.%0A%23minsources%202%0A%0A%23%20Allow%20NTP%20client%20access%20from%20local%20network.%0A%23allow%20192.168.0.0/16%0A%0A%23%20Serve%20time%20even%20if%20not%20synchronized%20to%20a%20time%20source.%0A%23local%20stratum%2010%0A%0A%23%20Require%20authentication%20%28nts%20or%20key%20option%29%20for%20all%20NTP%20sources.%0A%23authselectmode%20require%0A%0A%23%20Specify%20file%20containing%20keys%20for%20NTP%20authentication.%0Akeyfile%20/etc/chrony.keys%0A%0A%23%20Insert/delete%20leap%20seconds%20by%20slewing%20instead%20of%20stepping.%0A%23leapsecmode%20slew%0A%0A%23%20Get%20TAI-UTC%20offset%20and%20leap%20seconds%20from%20the%20system%20tz%20database.%0Aleapsectz%20right/UTC%0A%0A%23%20Specify%20directory%20for%20log%20files.%0Alogdir%20/var/log/chrony%0A%0A%23%20Select%20which%20information%20is%20logged.%0A%23log%20measurements%20statistics%20tracking }}
        mode: 420
        overwrite: true
        path: /etc/chrony.conf
      - contents:
          source: data:,
        mode: 420
        overwrite: true
        path: /etc/chrony.d/.mco-keep
      - contents:
          source: data:,{{ %23%0A%23%20This%20file%20controls%20the%20configuration%20of%20the%20ntp%20server%0A%23%20%7B%7B.var_multiple_time_servers%7D%7D%20we%20have%20to%20put%20variable%20array%20name%20here%20for%20mutilines%20remediation%0A%7B%7B%24var_time_service_set_maxpoll%3A%3D.var_time_service_set_maxpoll%7D%7D%0A%7B%7Brange%20%24element%3A%3D.var_multiple_time_servers%7CtoArrayByComma%7D%7Dserver%20%7B%7B%24element%7D%7D%20minpoll%204%20maxpoll%20%7B%7B%24var_time_service_set_maxpoll%7D%7D%0A%7B%7Bend%7D%7D }}
        mode: 420
        overwrite: true
        path: /etc/chrony.d/ntp-server.conf

Specify a Remote NTP Server

Description

Rationale

Remediation - Shell Script

Remediation - Kubernetes Patch