Epics@GSI Webhome

Tips Linux Dhclient Force Time Update

Introduction

Using dhclient exit hooks scripts allows to force an update of the system date using ntp/ntpd.

Similar to %FOREACH{"mytopic" in="TipsLinuxDhclientDynamicHostname"}% $mytopic %NEXT{"mytopic"}%

dhclient and its scripting capabilities on enter and exit hooks allows to react on dynamic network environments.

Provided you have root privileges this can be achieved by creating a script file ntp_force_update created in /etc/dhcp/dhclient-exit-hooks.d/ (on Debian), which is sourced by dhclient after having updated/received its DHCP informations.

#!/bin/sh
   # Filename:     /etc/dhcp/dhclient-exit-hooks.d/ntp_force_update
   # Purpose:      Used by dhclient-script to set the time of the system
   #
       
   # Do not update hostname for virtual machine IP assignments
   if [ "$interface" != "eth0" ] && [ "$interface" != "eth1" ] && [ "$interface" != "wlan0" ]
   then
           return
   fi
       
   if [ "$reason" != BOUND ] && [ "$reason" != RENEW ] && [ "$reason" != REBIND ] && [ "$reason" != REBOOT ]
   then
      return
   fi
     
   service ntp status >/dev/null 2>&1 && 
   (
     sleep 5 && 
     service ntp stop && 
     ntpd -qg ; 
     service ntp start; 
     touch /tmp/force_update
   ) &
   
    systemctl status systemd-timesyncd.service >/dev/null 2>&1 && 
   (
     sleep 5 && 
     systemctl status systemd-timesyncd.service stop && 
     timedatectl ; 
     systemctl status systemd-timesyncd.service start; 
     touch /tmp/force_update
   ) &
Applying those code lines: %FOREACH{"file" in="/etc/dhcp/dhclient-exit-hooks.d/ntp_force_update"}%
curl -s https://wiki.gsi.de/pub/Epics/TipsLinuxDhclientForceTimeUpdate/_etc_dhcp_dhclient-exit-hooks.d_ntp_force_update -o $file && 
   dos2unix $file && 
   chmod a+r $file
%NEXT{"file"}%

Local testing at the prompt:
dhclient


-- PeterZumbruch - 2018-05-02
-- PeterZumbruch - 2018-05-02

Topic attachments
I Attachment Action Size Date Who Comment
_etc_dhcp_dhclient-exit-hooks.d_ntp_force_updated_ntp_force_update _etc_dhcp_dhclient-exit-hooks.d_ntp_force_update manage 930 bytes 2018-05-02 - 16:31 PeterZumbruch /etc/dhcp/dhclient-exit-hooks.d/ntp_force_update
Topic revision: r3 - 2018-05-02, PeterZumbruch - This page was cached on 2021-10-19 - 22:30.

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