ntpdate-debian configuration file that screens NetworkManager's latest DHCP leases for NTP servers

ntpdate

# The settings in this file are used by the program ntpdate-debian, but not
# by the upstream program ntpdate.

# Set to "yes" to take the server list from /etc/ntp.conf, from package ntp,
# so you only have to keep it in one place.
NTPDATE_USE_NTP_CONF=yes

# List of NTP servers to use  (Separate multiple servers with spaces.)
# Not used if NTPDATE_USE_NTP_CONF is yes.
NTPSERVERS="ntp.ubuntu.com"

# Additional options to pass to ntpdate
NTPOPTIONS=""

# extract NTP servers from latest DHCP lease (if option was given by server)
get_debug_opts() {
    local opt
    debug_opt=false
    debug_syslog=false
    for opt in "$@" $( xargs -0 < /proc/$$/cmdline ); do
        case "$opt" in
            -d) debug_opt=true ;;
            -s) debug_syslog=true ;;
        esac
    done
    return 0
}

dhcp_ntp_debug_msg() {
    if $debug_opt; then
        echo "$(LC_ALL=C date +'%_d %b %H:%M:%S')" "ntpdate[$$]:" \
             '(DCHP)' "$@"
        if $debug_syslog; then
            logger --tag "ntpdate[$$]" '(DCHP)' "$@"
        fi
    fi
    return 0
}

get_dhcp_ntp_servers() {
    local debug_opt debug_syslog leasefiledir recentleasefile ntpservers

    leasefiledir=/var/lib/NetworkManager

    # check whether we are in debug mode and logging to syslog
    get_debug_opts $NTPOPTIONS

    # get most recent lease file that is not older than 1 minute
    recentleasefile=$( find $leasefiledir ! -type d -iname '*.lease' \
                            ! -mmin +1 -printf '%T@ %p\n' 2>/dev/null \
                         | sort -k 1nr | sed 's/^\S\+ //; 1q' )

    if [ -n "$recentleasefile" ]; then
        dhcp_ntp_debug_msg 'Found a recent lease file:' \
                           $( basename $recentleasefile )
        # extract NTP servers, if any  (check only latest lease in file)
        ntpservers=$( sed '1,/lease\s\+{/d
                           /option ntp-servers/!d
                           s/^.*ntp-servers\s\+\(.\+\);$/\1/; s/,/ /g' \
                        $recentleasefile )
        if [ -n "$ntpservers" ]; then
            dhcp_ntp_debug_msg 'Found NTP server(s) in latest lease:' \
                               $ntpservers
            NTPSERVERS="$ntpservers"
        else
            dhcp_ntp_debug_msg 'Latest lease does not contain any NTP servers.'
        fi
    else
        dhcp_ntp_debug_msg 'There is no recent lease file.'
    fi

    return 0
}

get_dhcp_ntp_servers

unset get_debug_opts dhcp_ntp_debug_msg get_dhcp_ntp_servers