How to use ntpdate behind a proxy?

Question

Is it possible to use ntpdate behind an HTTP proxy with authentication? In case it is not possible, are there any good alternatives?

Solution 1

This seems like a clear case for tlsdate.

 tlsdate: secure parasitic rdate replacement

  tlsdate sets the local clock by securely connecting with TLS to remote
  servers and extracting the remote time out of the secure handshake. Unlike
  ntpdate, tlsdate uses TCP, for instance connecting to a remote HTTPS or TLS
  enabled service, and provides some protection against adversaries that try
  to feed you malicious time information.

I do not think i have ever seen so many recommendations to use unsanitized data from internet as an argument to a sudo invocation.

Github: https://github.com/ioerror/tlsdate

Solution 2

Expanding on the answer by carveone:

sudo date -s "$(wget -S  "http://www.google.com/" 2>&1 | grep -E '^[[:space:]]*[dD]ate:' | sed 's/^[[:space:]]*[dD]ate:[[:space:]]*//' | head -1l | awk '{print $1, $3, $2,  $5 ,"GMT", $4 }' | sed 's/,//')"

Solution 3

One Liner

Assuming environment variable http_proxy is already set:

sudo date -s "$(curl -H'Cache-Control:no-cache' -sI google.com | grep '^Date:' | cut -d' ' -f3-6)Z"

we can verify the retrieved date/time first:

# local  date/time
date -d "$(curl -HCache-Control:no-cache -sI google.com | grep '^Date:' | cut -d' ' -f3-6)Z"

# or UTC date/time
date -ud "$(curl -HCache-Control:no-cache -sI google.com | grep '^Date:' | cut -d' ' -f3-6)"    

Notes

Just in case, certain options might be needed for curl:

• curl -x $proxy

  to explicitly set the proxy server to use, when the http_proxy environment variable is not set, default to protocol http and port 1080 (manual).

• curl -H 'Cache-Control: no-cache'

  to explicitly disable caching, especially when used in a cron job and/or behind a proxy server.

Alternate form tested with RHEL 6 that uses the '-u' option to date instead of appending the "Z" to the output:

sudo date -u --set="$(curl -H 'Cache-Control: no-cache' -sD - http://google.com |grep '^Date:' |cut -d' ' -f3-6)"

BTW, google.com is preferred over www.google.com, because the former results in a 301 redirect response, which is much smaller (569 vs 20k+ characters) but still good to use.

Solution 4

NTP service is using UDP protocol to sync the time. So HTTP/TCP proxy may not work for it. Alternative to accepted answer, there is a good htpdate tool to sync time behind proxy.

A cron job example:

* 3 * * * /usr/bin/htpdate -s -P <PROXY_HOST>:<PROXY__PORT> www.linux.org www.freebsd.org

Solution 5

If it is purely an HTTP proxy, it is using port 80, so the basic answer is no to that specifically. NTP uses UDP port 123. If it is a more generic proxy server, serving all ports, then maybe.

There are some programs out there that do NTP over HTTP. I do not use Linux, but this one might do it:

http://www.rkeene.org/oss/htp/ (still not sure if this will do authentication either).

I could not find one for Windows, but I will post back if I do.

View more solutions

Comments

[hicklypups]

Again for Linux, so I cannot add much other than a link: mina86.com/2010/01/16/ntp-over-http There might also be something that one of these publishes: nist.gov/pml/div688/grp40/softwarelist.cfm

[Ton van den Heuvel]

The NTP over HTTP link is inspiring, thanks for that!

[ryenus]

Caveat, this would create file 'index.html*' in the current directory.

[Hansi]

Note that the short version should use www.google.com since google.com is redirecting to it via 301 now with the date "stuck"

[SK23]

Thanks for the tip, I got it even easier: sudo date -s "$(curl -s http://www.timeapi.org/utc/now)" You don't need to pay attention to the timezone if your OS is set correctly. Linux recognizes the timezone provided in the string and sets the system time appropriately.

[Hansi]

When I made the comment the response for that command returned a day four days out of date.

[pabouk - Ukraine stay strong]

You should explain what is different in your solution in comparison to the answer by fiford_g.

[huzeyfe]

@ryenus This is a great answer. It works perfectly fine. However I have a problem when I put this command in a crontab job. Date's time part is made 00:00:00 whenever this job run. I tried to run in a shell script. Same result.

[ryenus]

@huzeyfe, would you please check if passing proxy to curl works?

[ryenus]

sudo date -s "$(wget -qSO- --max-redirect=0 google.com 2>&1 | grep Date: | cut -d' ' -f5-8)Z"

[ryenus]

^ above is the wget version, though I personally prefer using curl.

[dfc]

Passing unsanitized data from internet as a variable to a sudo invocation? Is it 1999?

[dfc]

yes, it works with proxies. I read the question too.

[user3655103]

zsh doesn't like the grep pattern without quotes around it; it results in (23) Failed writing body error. So when using zsh, use sudo date -s "$(curl -sD - google.com | grep '^Date:' | cut -d' ' -f3-6)Z" instead. There is probably a ZSH configuration modifier that changes this behavior, but I don't know what it is. Also, since we're talking about behind a proxy use, google.com seems to be cached by some proxies (being a 301 redirect) while www.google.com, being the live page, gets reloaded every time (and so its timestamp is accurate).

[Pi Delport]

This answer should really be at the top.

[Hi-Angel]

I didn't manage to get it work — with every combination it prints errors about false tickers. wget answer below does work.

[Alfabravo]

Have been working it out on a Centos6.9 machine but no joy. This seems more healthy than other recommendations but it is not trivial to get it working...

[Jay Taylor]

For a fully-working pre-baked implementation, see set_system_clock_from_google.sh.

[artificerpi]

Check my answer above.

[wisbucky]

tlsdate worked really well behind a proxy. But for Ubuntu, the only available package is for Xenial 16.04. It seems to be a dead project since the last commit was in 2015. As an alternative, try htpdate superuser.com/questions/307158/…

[Skippy le Grand Gourou]

It also has a -D (daemon) option.