Time Synchronisation: Difference between revisions
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== Default Time Source == |
== Default Time Source == |
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Windows AD domain members use the DC holding the [[Flexible_Single-Master_Operations_(FSMO) |
Windows AD domain members use the DC holding the [[Flexible_Single-Master_Operations_(FSMO)_Roles#PDC_Emulator|PDC emulator FSMO role]] as default time source. For more information about the time synchronisation and hierarchy in an AD, see http://technet.microsoft.com/en-us/library/cc773013%28v=ws.10%29.aspx#w2k3tr_times_how_izcr. |
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Revision as of 13:58, 9 October 2016
Introduction
In an Active Directory (AD) you must have an accurate time synchronisation. For example, Kerberos requires correct time stamps to prevent replay attacks and the AD uses the time to resolve replication conflicts. The default maximum allowed time deviation in an AD is 5 minutes. If a domain member or domain controller (DC) has a higher or lower time difference, the access is denied. As a result, a user cannot access shares or query the directory.
Samba supports the "ntpd" from http://ntp.org. The daemon synchronises the time with external sources and enables clients to retrieve the time from the server running the daemon.
Note that "ntpd" does not support authenticated time synchronisation with Windows 2000 clients.
Configuring Time Synchronisation on a DC
Requirements
- ntpd >= 4.2.6 from http://www.ntp.org, compiled with enabled signed ntp support ("--enable-ntp-signd")
- Verify the socket permissions on your domain controller (DC). The "ntpd" daemon must have read permissions in the "ntp_signed" directory. To list the permissions, enter:
# ls -ld /usr/local/samba/var/lib/ntp_signd/ drwxr-x--- 2 root ntp 4096 1. May 09:30 /usr/local/samba/var/lib/ntp_signd/
- To set the permissions, run:
# chown root:ntp /usr/local/samba/var/lib/ntp_signd/ # chmod 750 /usr/local/samba/var/lib/ntp_signd/
Set up the ntpd.conf File on a DC
Typically, the "ntpd" daemon read its configuration from the /etc/ntpd.conf file.
The following is a minimum "ntpd.conf" file that synchronises the time with three external NTP server and enables clients to query the time using signed NTP requests:
# Local clock. Note that is not the "localhost" address! server 127.127.1.0 fudge 127.127.1.0 stratum 10 # Where to retrieve the time from server 0.pool.ntp.org iburst prefer server 1.pool.ntp.org iburst prefer server 2.pool.ntp.org iburst prefer driftfile /var/lib/ntp/ntp.drift logfile /var/log/ntp ntpsigndsocket /usr/local/samba/var/lib/ntp_signd/ # Access control # Default restriction: Allow clients only to query the time restrict default kod nomodify notrap nopeer mssntp # No restrictions for "localhost" restrict 127.0.0.1 # Enable the time sources to only provide time to this host restrict 0.pool.ntp.org mask 255.255.255.255 nomodify notrap nopeer noquery restrict 1.pool.ntp.org mask 255.255.255.255 nomodify notrap nopeer noquery restrict 2.pool.ntp.org mask 255.255.255.255 nomodify notrap nopeer noquery
For further information about the "ntpd" access control, see http://support.ntp.org/bin/view/Support/AccessRestrictions.
If you have SELinux enabled on your server, see Time Synchronisation - SELinux Labeling and Policy.
Configuring Time Synchronisation on a Linux Domain Member
Requirements
- ntpd from http://www.ntp.org.
Set up the ntpd.conf File on a Linux Domain Member
Typically, the "ntpd" daemon read its configuration from the /etc/ntpd.conf file.
The following is a minimum "ntpd.conf" file that synchronises the time with the Samba Active Directory (AD) domain controllers (DC) "DC1" and "DC2" and does not provide time services for other hosts.
# Local clock. Note that is not the "localhost" address! server 127.127.1.0 fudge 127.127.1.0 stratum 10 # Where to retrieve the time from server DC1.samdom.example.com iburst prefer server DC2.samdom.example.com iburst driftfile /var/lib/ntp/ntp.drift logfile /var/log/ntp # Access control # Default restriction: Disallow everything restrict default ignore # No restrictions for "localhost" restrict 127.0.0.1 # Enable the time sources only to only provide time to this host restrict DC1.samdom.example.com mask 255.255.255.255 nomodify notrap nopeer noquery restrict DC2.samdom.example.com mask 255.255.255.255 nomodify notrap nopeer noquery
For further information about the "ntpd" access control, see http://support.ntp.org/bin/view/Support/AccessRestrictions.
Configuring Time Synchronisation on a Windows Domain Member
Default Time Source
Windows AD domain members use the DC holding the PDC emulator FSMO role as default time source. For more information about the time synchronisation and hierarchy in an AD, see http://technet.microsoft.com/en-us/library/cc773013%28v=ws.10%29.aspx#w2k3tr_times_how_izcr.
Setting User Defined Time Sources and Options
To configure a different time source than the domain controller (DC) holding the PDC emulator FSMO role:
- Open the Group Policy Management Console (GPMC).
- To install, see Installing the Remote Server Administration Tools (RSAT).
- Create a new group policy object (GPO).
- Right-click the GPO and select "Edit".
- In the Group Policy Management Editor (GPME) navigate to "Computer Configuration" / "Administrative Templates" / "System" / "Windows Time Service" / "Time Providers".
- Edit the "Configure Windows NTP Client" policy:
- To set "DC2.samdom.example.com" as the only and primary time source ("0x9") using the NTP protocol:
- For descriptions on the other options in the screen capture, see the GPO help.
- Save the GPO
- Link the GPO to a organizational unit (OU) or to the domain.