jaytaylor/._set_system_clock_from_google.md

## ._set_system_clock_from_google.md

      
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              ._set_system_clock_from_google.md
            
          
    set_system_clock_from_google.sh

Sets system time based on what is reported by google.com.  Useful for cases where it is not possible to use the standard ntpdate command.  For eample, if a Linux machine is on a network which is only able to reach the internet through an HTTP proxy.
Inspired by ryenus' answer @ https://superuser.com/a/807326/72342
Installation

# Download latest set_system_clock_from_google.sh script.
curl -sS --remote-name-all $( \
    curl -sS https://api.github.com/gists/60c8a4e22431c4271200cab68186deb7 \
        | jq -r '.files[].raw_url' \
        | grep -v '\/\._' \
)

# Set permissions and move to local sbin.
chmod a+x set_system_clock_from_google.sh
sudo chown root:root set_system_clock_from_google.sh
sudo mv set_system_clock_from_google.sh /usr/local/sbin/
Cronjob Scheduling

Here is a command to install a cronjob which syncs the system clock at the top of every hour:
(sudo crontab -l 2>/dev/null; echo '1 * * * * /usr/local/sbin/set_system_clock_from_google.sh') \
    | sudo crontab -
Verify installation

List all root cronjobs and verify the job has been added:
sudo crontab -l
Example output

1 * * * * /usr/local/sbin/set_system_clock_from_google.sh

Run or test it manually

Verbose output is available when the -v flag is passed.
/usr/local/sbin/set_system_clock_from_google.sh -v

  
## set_system_clock_from_google.sh
#!/usr/bin/env bash

##
# @author Jay Taylor (https://jaytaylor.com)
#
# @date 2018-08-28
#
# @description Sets system time based on what is reported by google.com.  Useful
# for cases when you have a Linux machine on a network which is only able to
# reach the internet through an HTTP proxy.
#
# Inspired by ryenus' answer @ https://superuser.com/a/807326/72342
#

set -o errexit
set -o pipefail
set -o nounset

if [ "${UID:-}" != '0' ]; then
    echo "ERROR: $0 must be run as root" 1>&2
    exit 1
fi

if [ "${1:-}" = '-v' ]; then
    set -o xtrace
    shift
fi

utc_stamp="$( \
    curl --head -sS -H 'Cache-Control: no-cache' 'https://google.com/' \
        | grep '^Date:' \
        | cut -d' ' -f3-6 \
)Z"

if [ "${utc_stamp}" = 'Z' ]; then
    echo 'ERROR: setting system clock aborted due to empty $utc_stamp var value' 1>&2
    exit 1
fi

echo "INFO: setting system clock to: ${utc_stamp}" 1>&2
date -s "${utc_stamp}"
	#!/usr/bin/env bash

	##
	# @author Jay Taylor (https://jaytaylor.com)
	#
	# @date 2018-08-28
	#
	# @description Sets system time based on what is reported by google.com. Useful
	# for cases when you have a Linux machine on a network which is only able to
	# reach the internet through an HTTP proxy.
	#
	# Inspired by ryenus' answer @ https://superuser.com/a/807326/72342
	#

	set -o errexit
	set -o pipefail
	set -o nounset

	if [ "${UID:-}" != '0' ]; then
	echo "ERROR: $0 must be run as root" 1>&2
	exit 1
	fi

	if [ "${1:-}" = '-v' ]; then
	set -o xtrace
	shift
	fi

	utc_stamp="$( \
	curl --head -sS -H 'Cache-Control: no-cache' 'https://google.com/' \
	\| grep '^Date:' \
	\| cut -d' ' -f3-6 \
	)Z"

	if [ "${utc_stamp}" = 'Z' ]; then
	echo 'ERROR: setting system clock aborted due to empty $utc_stamp var value' 1>&2
	exit 1
	fi

	echo "INFO: setting system clock to: ${utc_stamp}" 1>&2
	date -s "${utc_stamp}"