How to use ntpdate behind a proxy?
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", $4 }' | sed 's/,//')"
This seems like a clear case for tlsdate.
tlsdate: secure parasitic rdate replacement
tlsdate sets the local clock by securely connecting with TLS to remote
servers and extracting the remote time out of the secure handshake. Unlike
ntpdate, tlsdate uses TCP, for instance connecting to a remote HTTPS or TLS
enabled service, and provides some protection against adversaries that try
to feed you malicious time information.
I do not think i have ever seen so many recommendations to use unsanitized data from internet as an argument to a sudo invocation.
Github: https://github.com/ioerror/tlsdate
One Liner
Assuming environment variable http_proxy
is already set:
sudo date -s "$(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 $proxy
to explicitly set the proxy server to use, when the
http_proxy
environment variable is not set, default to protocolhttp
and port1080
(manual).curl -H 'Cache-Control: no-cache'
to explicitly disable caching, especially when used in a cron job and/or behind a proxy server.
Alternate form tested with RHEL 6 that uses the '-u' option to date instead of appending the "Z" to the output:
sudo date -u --set="$(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.