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httpdate - set local date and time from a web server

Posted by Daniel Lange on
Linux

While ntp may be a great protocol, I find it quite bloated and slow for the simple purpose of just setting a local date and time to a reference clock. I do not need 20ms accuracy on a notebook's clock :-). Thus I use(d) rdate for a decade now but the public rdate servers are slowly dying out. So I'm replacing it more and more with htpdate which works quite nicely. It's written in C and a perl alternative is available on the author's site. There is also a forked windows version of it available.

Developing a bit larger bash script (which syncs a few servers), I wondered whether I could realize the time sync part in bash as well.

It's quite possible:

  1. # open a tcp connection to www.google.com
  2. exec 3<>/dev/tcp/www.google.com/80
  3. # say hello HTTP-style
  4. echo -e "GET / HTTP/1.0\n\n">&3
  5. # parse for a Date: line and with a bit of magic throw the date-string at the date command
  6. LC_ALL=C LANG=en date --rfc-2822 --utc -s "$(head <&3 | grep -i "Date: " | sed -e s/Date\:\ //I)"
  7. # close the tcp connection
  8. exec 3<&-

Simple, eh?

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