A tool to synchronize system time from web servers, for linux, windows and macos.

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README.md

htpdate

A tool to synchronize system time from web servers, for linux, windows and macos. Download

Examples

Synchronize time from multiple URLs

htpdate -s www.pool.ntp.org www.openssl.org nodejs.org

Query time from multiple URLs

htpdate www.pool.ntp.org www.openssl.org nodejs.org

Change default protocol to 'http'

htpdate -s -p http www.pool.ntp.org

Mix http and https URLs

htpdate -s http://www.pool.ntp.org https://www.openssl.org

Access through a http proxy

export http_proxy=http://127.0.0.1:8118
htpdate -s www.pool.ntp.org

Usage

htpdate [options...] URLs...

Options

 -c, --count            The number of requests for each URL
                        Default: 4

 -C, --command          Command to adjust system time, in https://day.js.org/ UTC format
                        Default(Linux/Mac): '[date --utc -set=]YYYY-MM-DDTHH:mm:ss.SSS'
                        Default(Windows): '[wmic OS Set localdatetime=]YYYYMMDDmmss.SSS[000][+000]'

 -h, --help             This help text
                        Default: false

     --http2            Try to choose either HTTP/1.1 or HTTP/2 depending on the ALPN protocol
                        Default: false

 -i, --interval         The minimum milliseconds between requests
                        Default: 500

 -k, --insecure         Allow insecure server connections when using https
                        Default: false

 -m, --method           HTTP method
                        Default: 'HEAD'

 -p, --protocol         Use this protocol when no protocol is specified in the URL
                        Default: 'https'

 -r, --retry
                        Default: 0

 -R, --redirect         If redirect responses should be followed
                        Default: false

 -s, --set              Adjust system time if necessary
                        Default: false

 -t, --threshold        At least how many milliseconds are considered to adjust system time
                        Default: 1500

 -T, --timeout
                        Default: 6000

 -u, --user-agent
                        Type: string

 -V, --version          display the version of htpdate and exit
                        Default: false

 -v, --verbose          Make the operation more talkative
                        Default: false

Install Precompiled package

Download the precompiled binary package from Releases page, uncompress it, and run it independently as an executable.

Compile

git clone https://github.com/bobwen-dev/htpdate
cd htpdate
npm install
npm run build

The principle

Website returns a header Date in each response, like this:

HTTP/2 200
Content-Type: text/html; charset=utf-8
Date: Wed, 03 Nov 2021 11:46:19 GMT
...

This Date: Wed, 03 Nov 2021 11:46:19 GMT is the moment the website was processing the request, which is between the time we sent the request and the time we received the response. Simply assuming that the period to send request and receive is equal, we can calculate that the difference between local time and website time:

duration = received_at - sent_at
delta = server_time - received_at - duration / 2

There is one more thing: the precision of Date. Imagine you get a Date end with :23 GMT, which could be 23.000 seconds, or 23.999 seconds. So we give +0.5s as a compensation.

License

Licensed under the GNU Affero General Public License v3.0 or later.