Set local date to remote host's date by means of ssh

ghetto-ntp

#!/bin/sh

set -eu

usage() {
  local basename
  basename="$(basename "$0")"

  cat<<USAGE
Usage:
  $basename [USER@]REMOTEHOST [SSH_OPTIONS]...

Sets the date on this host to the date on REMOTEHOST.

Getting the remote date requires opening an ssh connection to a remote sshd,
and setting it requires root privilege.

Ensure the timezone on both hosts is correct.

USAGE
  exit 127
}

[ $# -lt 1 ] && usage
ssh_args=$*

echo "Getting the remote date..."
# -u specifies UTC and %s formats in epoch seconds
theirs="$(ssh $ssh_args date -u +%s)"
ours="$(date -u +%s)"

echo "Setting local date..."
newdate="$(date -u -s "@$theirs")"

printf '%s\t%s\n' "Old date:" "$(date -d "@$ours")"
printf '%s\t%s\n' "New date:" "$newdate"
printf '%s %d %s\n\n' "Clock adjusted by" "$((theirs - ours))" "sec."