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[http://www.ietf.org/rfc/rfc868.txt rdate] is an antiquated method of time and date synchronization between Unix machines.  The service is a daemon listening on port 37, which when you connect to it, returns 4 bytes: the Unix timestamp (number of seconds since Jan 1 1970).  The client program (rdate) doesn't try to account for network delays, nor continuously correct the clock, like the more modern ntpd (network time protocol daemon): it's just a one-shot synchronization.  However it can be useful on embedded systems because [http://busybox.net/downloads/BusyBox.html busybox] conveniently provides the rdate client.
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[http://www.ietf.org/rfc/rfc868.txt rdate] is an antiquated method of time and date synchronization between Unix machines.  The service is a daemon listening on port 37, which when you connect to it, returns 4 bytes: the Unix timestamp (number of seconds since Jan 1 1970) and then drops the connection.  The client program (rdate) doesn't try to account for network delays, nor continuously correct the clock, like the more modern ntpd (network time protocol daemon): it's just a one-shot synchronization.  However it can be useful on embedded systems because [http://busybox.net/downloads/BusyBox.html busybox] conveniently provides the rdate client.
  
 
So how do you set up an rdate server?  [http://argray.com/unixfaq/timesync.shtml#rdate_server This page] says "don't bother," but I didn't find that a very acceptable answer.
 
So how do you set up an rdate server?  [http://argray.com/unixfaq/timesync.shtml#rdate_server This page] says "don't bother," but I didn't find that a very acceptable answer.
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  #      only_from      = localhost
 
  #      only_from      = localhost
  
Security wonks have been spoiling a lot of the fun on the Internet for a while now, so useful little gems like this tend to be disabled by default lest they be exploitable.  Somehow I doubt this one poses much risk.
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Security wonks have been spoiling a lot of the fun on the Internet for a while now, so useful little gems like this tend to be disabled by default lest they be exploitable.  Somehow I doubt this one poses much risk, since it's a one-way conversation.  Hopefully xinetd's implementation doesn't have buffer-overflow bugs.

Revision as of 16:55, 9 January 2008

rdate is an antiquated method of time and date synchronization between Unix machines. The service is a daemon listening on port 37, which when you connect to it, returns 4 bytes: the Unix timestamp (number of seconds since Jan 1 1970) and then drops the connection. The client program (rdate) doesn't try to account for network delays, nor continuously correct the clock, like the more modern ntpd (network time protocol daemon): it's just a one-shot synchronization. However it can be useful on embedded systems because busybox conveniently provides the rdate client.

So how do you set up an rdate server? This page says "don't bother," but I didn't find that a very acceptable answer.

xinetd

xinetd has rdate support built-in. The conf file /etc/xinetd.d/time-stream describes how it is to be offered. The default configuration is OK except that you need to change the line

disable = yes

to disable = no. And also comment out this line in /etc/xinetd.conf:

#       only_from       = localhost

Security wonks have been spoiling a lot of the fun on the Internet for a while now, so useful little gems like this tend to be disabled by default lest they be exploitable. Somehow I doubt this one poses much risk, since it's a one-way conversation. Hopefully xinetd's implementation doesn't have buffer-overflow bugs.