network-scripts/network-functions - main - githubmirror/initscripts

network-scripts/network-functions
744 строки20 KB
Rohit Nair
network-functions: Fix a bug in is_nm_handling()
19 сен 2024, 14:02
19 сен 2024, 14:025c61fd7
# -*-Shell-script-*-
#
# This file is not a stand-alone shell script; it provides functions 
# to network scripts that source it.

# Set up a default search path.
PATH="/sbin:/usr/sbin:/bin:/usr/bin"
export PATH

# We need to initialize the $HOSTNAME variable by ourselves now:
# (It was previously done for RHEL-6 branch, but got lost in time.)
HOSTNAME="$(hostname)"

[ -z "$__sed_discard_ignored_files" ] && . /etc/init.d/functions

get_hwaddr ()
{
    if [ -f /sys/class/net/${1}/address ]; then
        tr '[a-z]' '[A-Z]' < /sys/class/net/${1}/address
    elif [ -d "/sys/class/net/${1}" ]; then
        LC_ALL= LANG= ip -o link show ${1} 2>/dev/null | \
            awk '{ print toupper(gensub(/.*link\/[^ ]* ([[:alnum:]:]*).*/,
                                        "\\1", 1)); }'
    fi
}

get_config_by_device ()
{
    LANG=C grep -l "^[[:space:]]*DEVICE=['\"]\?${1}['\"]\?\([[:space:]#]\|$\)" \
        /etc/sysconfig/network-scripts/ifcfg-* \
        | LC_ALL=C sed -e "$__sed_discard_ignored_files"
}

get_config_by_hwaddr ()
{
    LANG=C grep -il "^[[:space:]]*HWADDR=['\"]\?${1}['\"]\?\([[:space:]#]\|$\)" /etc/sysconfig/network-scripts/ifcfg-* \
        | LC_ALL=C sed -e "$__sed_discard_ignored_files"
}

get_config_by_subchannel ()
{
    LANG=C grep -E -i -l \
        "^[[:space:]]*SUBCHANNELS=['\"]?([0-9]\.[0-9]\.[a-f0-9]+,){0,2}${1}(,[0-9]\.[0-9]\.[a-f0-9]+){0,2}['\"]?([[:space:]]+#|[[:space:]]*$)" \
        /etc/sysconfig/network-scripts/ifcfg-* \
        | LC_ALL=C sed -e "$__sed_discard_ignored_files"
}

get_config_by_name ()
{
    LANG=C grep -E -i -l "^[[:space:]]*NAME=\"(Auto |System )?${1}\"" \
        /etc/sysconfig/network-scripts/ifcfg-* \
        | LC_ALL=C sed -e "$__sed_discard_ignored_files"
}

get_device_by_hwaddr ()
{
    LANG=C ip -o link | awk -F ': ' -vIGNORECASE=1 '!/link\/ieee802\.11/ && /'"$1"'/ { print $2 }'
}

get_uuid_by_config ()
{
    dbus-send --system --print-reply --dest=com.redhat.ifcfgrh1 /com/redhat/ifcfgrh1 com.redhat.ifcfgrh1.GetIfcfgDetails string:"/etc/sysconfig/network-scripts/$1" 2>/dev/null | awk -F '"' '/string / { print $2 }'
}

generate_lease_file_name ()
{
    local ver=$1
    LEASEFILE="/var/lib/dhclient/dhclient$ver-${DEVICE}.leases"
    if [ -f $LEASEFILE ]; then
         return
    fi
    LEASEFILE="/var/lib/dhclient/dhclient$ver-${UUID}-${DEVICE}.lease"
}

generate_config_file_name ()
{
    local ver=$1
    if [ -s /etc/dhcp/dhclient$ver-${DEVICE}.conf ]; then
        DHCLIENTCONF="-cf /etc/dhcp/dhclient$ver-${DEVICE}.conf";
    elif [ -s /etc/dhclient$ver-${DEVICE}.conf ]; then
        DHCLIENTCONF="-cf /etc/dhclient$ver-${DEVICE}.conf";
    else
        DHCLIENTCONF='';
    fi
}

need_config ()
{
    local nconfig

    CONFIG="ifcfg-${1}"
    [ -f "${CONFIG}" ] && return
    CONFIG="${1##*/}"
    [ -f "${CONFIG}" ] && return
    nconfig=$(get_config_by_name "${1}")
    if [ -n "$nconfig" ] && [ -f "$nconfig" ]; then
        CONFIG=${nconfig##*/}
        return
    fi
    local addr=$(get_hwaddr ${1})
    if [ -n "$addr" ]; then
        nconfig=$(get_config_by_hwaddr ${addr})
        if [ -n "$nconfig" ] ; then
            CONFIG=${nconfig##*/}
            [ -f "${CONFIG}" ] && return
        fi
    fi
    nconfig=$(get_config_by_device ${1})
    if [ -n "$nconfig" ] && [ -f "$nconfig" ]; then
        CONFIG=${nconfig##*/}
        return
    fi
}

source_config ()
{
    CONFIG=${CONFIG##*/}
    DEVNAME=${CONFIG##ifcfg-}
    . /etc/sysconfig/network-scripts/$CONFIG
    [ -r "keys-$DEVNAME" ] && . /etc/sysconfig/network-scripts/keys-$DEVNAME
    case "$TYPE" in
    Ethernet)
        DEVICETYPE="eth"
        ;;
    CIPE)
        DEVICETYPE="cipcb"
        ;;
    IPSEC)
        DEVICETYPE="ipsec"
        ;;
    Modem)
        DEVICETYPE="ppp"
        ;;
    xDSL)
        DEVICETYPE="ppp"
        ;;
    ISDN)
        DEVICETYPE="ippp"
        ;;
    Wireless)
        DEVICETYPE="eth"
        ;;
    "Token Ring")
        DEVICETYPE="eth"
        ;;
    CTC)
        DEVICETYPE="ctc"
        ;;
    GRE | GRE6 | IPIP | IPIP6)
        DEVICETYPE="tunnel"
        ;;
    SIT | sit)
        DEVICETYPE="sit"
        ;;
    InfiniBand | infiniband)
        DEVICETYPE="ib"
        ;;
    OVS*)
        DEVICETYPE="ovs"
        ;;
    Bridge)
        DEVICETYPE="eth"
        ;;
    esac
    if [ -n "$HWADDR" ]; then
        HWADDR=$(echo "$HWADDR" | tr '[a-z]' '[A-Z]')
    fi
    if [ -n "$MACADDR" ]; then
        MACADDR=$(echo "$MACADDR" | tr '[a-z]' '[A-Z]')
    fi
    [ -z "$DEVICE" -a -n "$HWADDR" ] && DEVICE=$(get_device_by_hwaddr $HWADDR)
    [ -z "$DEVICETYPE" ] && DEVICETYPE=$(echo ${DEVICE} | sed "s/[0-9]*$//")
    [ -z "$REALDEVICE" -a -n "$PARENTDEVICE" ] && REALDEVICE=$PARENTDEVICE
    [ -z "$REALDEVICE" ] && REALDEVICE=${DEVICE%%:*}
    [ -z "$SYSCTLDEVICE" ] && SYSCTLDEVICE=${REALDEVICE/.//}
    if [ "${DEVICE}" != "${REALDEVICE}" ]; then
        ISALIAS=yes
    else
        ISALIAS=no
    fi
    if is_nm_running && [ "$REALDEVICE" != "lo" ] ; then
        nm_con_load "$CONFIG"
        if ! is_false $NM_CONTROLLED; then
            UUID=$(get_uuid_by_config $CONFIG)
            [ -n "$UUID" ] && _use_nm=true
        fi
    fi
}

nm_con_load () {
    dbus-send --system --print-reply \
        --dest=org.freedesktop.NetworkManager \
        /org/freedesktop/NetworkManager/Settings \
        org.freedesktop.NetworkManager.Settings.LoadConnections \
        array:string:"/etc/sysconfig/network-scripts/${1}" >/dev/null 2>&1
}

ethtool_set ()
{
    if [ -n "${ETHTOOL_OPTS}" ] && [ ! -x /sbin/ethtool ] ; then
        net_log "ethtool does not exist or is not executable." warning
    else
        oldifs=$IFS;
        IFS=';';
        if [ -n "${ETHTOOL_DELAY}" ] ; then
            # Convert microseconds to seconds:
            local ETHTOOL_DELAY_SEC=$(convert2sec ${ETHTOOL_DELAY} micro)
            sleep ${ETHTOOL_DELAY_SEC}
        fi
        for opts in $ETHTOOL_OPTS ; do
            IFS=$oldifs;
            if [[ "${opts}" =~ [[:space:]]*- ]] ; then
                /sbin/ethtool $opts
            else
                /sbin/ethtool -s ${REALDEVICE} $opts
            fi
            IFS=';';
        done
        IFS=$oldifs;
    fi
}

expand_config ()
{
    local i=0 val
    for idx in '' {0..255} ; do
        ipaddr[$i]=$(eval echo '$'IPADDR$idx)
        if [ -z "${ipaddr[$i]}" ]; then
            [ "$idx" ] && [ $idx -ge 2 ] && break
            continue
        fi
        prefix[$i]=$(eval echo '$'PREFIX$idx)
        netmask[$i]=$(eval echo '$'NETMASK$idx)
        broadcast[$i]=$(eval echo '$'BROADCAST$idx)
        arpcheck[$i]=$(eval echo '$'ARPCHECK$idx)
        arpupdate[$i]=$(eval echo '$'ARPUPDATE$idx)

        if [ "${prefix[$i]}x" != "x" ]; then
            val=$(/bin/ipcalc --netmask "${ipaddr[$i]}/${prefix[$i]}")
            netmask[$i]=${val##NETMASK=}
        fi

        if [ "${netmask[$i]}x" = "x" ]; then
            val=$(/bin/ipcalc --netmask "${ipaddr[$i]}")
            netmask[$i]=${val##NETMASK=}
        fi

        if [ "${prefix[$i]}x" = "x" ]; then
            val=$(/bin/ipcalc --prefix ${ipaddr[$i]} ${netmask[$i]})
            prefix[$i]=${val##PREFIX=}
        fi

        if [ "${broadcast[$i]}x" = "x" ]; then
            val=$(/bin/ipcalc --broadcast ${ipaddr[$i]} ${netmask[$i]})
            broadcast[$i]=${val##BROADCAST=}
        fi

        if [ "${arpcheck[$i]}x" != "x" ]; then
            arpcheck[$i]=${arpcheck[$i]##ARPCHECK=}
            arpcheck[$i]=${arpcheck[$i],,*}
        fi

        if [ "${arpupdate[$i]}x" != "x" ]; then
            arpupdate[$i]=${arpupdate[$i]##ARPUPDATE=}
            arpupdate[$i]=${arpupdate[$i],,*}
        fi

        i=$((i+1))
    done

    [ -n "$DHCP_HOSTNAME" ] && DHCP_HOSTNAME=${DHCP_HOSTNAME%%.*}

    if [ -z "${NETWORK}" ]; then
        eval $(/bin/ipcalc --network ${ipaddr[0]} ${netmask[0]})
    fi
}

toggle_value ()
{
    if is_true "$2"; then
        echo "$1 on"
    elif is_false "$2"; then
        echo "$1 off"
    else
        echo ''
    fi
}

is_nm_running ()
{
    dbus-send --system --print-reply \
        --dest=org.freedesktop.DBus \
        /org/freedesktop/DBus \
        org.freedesktop.DBus.GetNameOwner \
        string:"org.freedesktop.NetworkManager" >/dev/null 2>&1
}

is_nm_active ()
{
    LANG=C nmcli -t --fields device,state dev status 2>/dev/null | grep -q "^${1}:connected$"
}

is_nm_handling ()
{
    LANG=C nmcli -t --fields device,state dev status 2>/dev/null | grep -q "^\(${1}:connected\|${1}:connecting.*\)$"
}

is_nm_device_unmanaged ()
{
    LANG=C nmcli -t --fields GENERAL dev show "${1}" 2>/dev/null | awk -F ':' '/GENERAL.STATE/ { if ($2 == "unmanaged") exit 0 ; else exit 1; }'
}

# Sets $alias to the device module if $? != 0
is_available ()
{
    [ -z "$1" ] && return 1

    [ -d "/sys/class/net/$1" ] && return 0

    [ -n "$BONDING_OPTS" ] && install_bonding_driver $1

    alias=$(modprobe -c | awk \
        'BEGIN { alias = ""; }
        $1 == "alias" && $2 == "'"$1"'" { alias = $3; }
        $1 == "install" { install[$2] = $3; }
        END {
            cmd = install[alias];
            print alias;
            if (alias == "" || alias == "off" || cmd == "/bin/true" || cmd == ":")
                exit 1;
            exit 0;
        }
    ')
    [ $? -eq 0 ] || return 2

    modprobe $1 > /dev/null 2>&1 || {
        return 1
    }
    if [ -n "$HWADDR" ]; then
        local curdev=$(get_device_by_hwaddr "$HWADDR")
        if [ -z "$curdev" ]; then
            return 1
        fi
    fi

    if [ ${alias} = "bonding" ]; then
        install_bonding_driver $1
    fi

    [ -d "/sys/class/net/$1" ] && return 0 || return 1
}

is_available_wait ()
{
    [ -z "$1" ] && return 1

    local retry=${2##*[!0-9]*}

    is_available $1 && return 0
    ret=$?

    while [ 0"$retry" -gt 0 ]; do
        sleep 1
        [ -d "/sys/class/net/$1" ] && return 0
        retry=$(($retry -1))
    done

    return $ret
}

is_hostname_set ()
{
    case "${HOSTNAME}" in
        '(none)' | 'localhost' | 'localhost.localdomain')
            # Hostname NOT set:
            return 1
            ;;
        *)
            # Hostname IS set:
            return 0
            ;;
    esac
}

need_hostname ()
{
    # Should we avoid obtaining hostname from DHCP? (user override)
    is_true "${NO_DHCP_HOSTNAME}" && return 1

    if is_hostname_set; then
        # Hostname is already set, we do not need to acquire it:
        return 1
    else
        # Hostname is NOT set, we need to acquire it:
        return 0
    fi
}

set_hostname_options ()
{
    # User explicitly requires to *not* send DHCP_HOSTNAME, DHCP_FQDN or HOSTNAME:
    is_false "${DHCP_SEND_HOSTNAME}" && return

    if [[ -n "${DHCP_HOSTNAME}" && -n "${DHCP_FQDN}" ]]; then
        net_log $"Both 'DHCP_HOSTNAME=${DHCP_HOSTNAME}' and 'DHCP_FQDN=${DHCP_FQDN}' are configured... Using DHCP_FQDN." warning
    fi

    local hostname_options=''

    # DHCP_FQDN takes precedence before DHCP_HOSTNAME -- as it does in NetworkManager,
    # and DHCP_HOSTNAME takes precedence before HOSTNAME:
    if [[ -n "${DHCP_FQDN}" ]]; then
        hostname_options="-F ${DHCP_FQDN}"
    elif [[ -n "${DHCP_HOSTNAME}" ]]; then
        hostname_options="-H ${DHCP_HOSTNAME}"
    elif is_hostname_set; then
        # We need to truncate the hostname in case it is the FQDN:
        hostname_options="-H ${HOSTNAME%%.*}"
    else
        # Nothing to send to the DHCP server:
        # ['(none)', 'localhost' or 'localhost.localdomain' are not valid]
        return
    fi

    # Append the hostname options to the content of passed variable name:
    eval "$1='${!1} ${hostname_options}'"

    return
}

set_hostname ()
{
    hostname $1
    if ! grep search /etc/resolv.conf >/dev/null 2>&1; then
        domain=$(echo $1 | sed 's/^[^\.]*\.//')
        if [ -n "$domain" ]; then
            rsctmp=$(mktemp /tmp/XXXXXX);
            cat /etc/resolv.conf > $rsctmp
            echo "search $domain" >> $rsctmp

            # Backup resolv.conf only if it doesn't exist already:
            ! [ -f /etc/resolv.conf.save ] && cp -af /etc/resolv.conf /etc/resolv.conf.save

            change_resolv_conf $rsctmp
            /bin/rm -f $rsctmp
        fi    
    fi
}

check_device_down ()
{
    [ ! -d /sys/class/net/$1 ] && return 0
    if LC_ALL=C ip -o link show dev $1 2>/dev/null | grep -q ",UP" ; then
        return 1
    else
        return 0
    fi
}

set_link_up ()
{
    if [ "$LINKSTATUS" != down ]; then
        ip link set dev $1 up >/dev/null 2>&1
    fi
}

check_link_down ()
{
    if ! LC_ALL=C ip link show dev $1 2>/dev/null| grep -q ",UP" ; then
        set_link_up $1
    fi

    timeout=0
    delay=10
    [ -n "$LINKDELAY" ] && delay=$(($LINKDELAY * 2))
    while [ $timeout -le $delay ]; do
        [ "$(cat /sys/class/net/$REALDEVICE/carrier 2>/dev/null)" != "0" ] && return 1
        sleep 0.5
        timeout=$((timeout+1))
    done
    return 0
}

check_default_route ()
{
    LC_ALL=C ip route list match 0.0.0.0/0 | grep -q default
}

find_gateway_dev ()
{
    . /etc/sysconfig/network
    if [ -n "${GATEWAY}" -a "${GATEWAY}" != "none" ] ; then
        dev=$(LC_ALL=C /sbin/ip route get to "${GATEWAY}" 2>/dev/null | \
        sed -n 's/.* dev \([[:alnum:]]*\) .*/\1/p')
        if [ -n "$dev" ]; then
            GATEWAYDEV="$dev"
        fi
    fi
}

# After the device $1 goes away, restore the standard default route; typically
# used for ppp with DEFROUTE temporarily replacing the "standard" default
# route.
# FIXME: This function doesn't support some newer features (GATEWAY in ifcfg,
# $WINDOW, $METRIC)
add_default_route ()
{
    . /etc/sysconfig/network
    check_default_route && return 0
    find_gateway_dev
    if [ "$GATEWAYDEV" != "" -a -n "${GATEWAY}" -a \
             "${GATEWAY}" != "none" ]; then
        if ! check_device_down $1; then
            if [ "$GATEWAY" = "0.0.0.0" ]; then
                /sbin/ip route add default dev ${GATEWAYDEV}
            else
                /sbin/ip route add default via ${GATEWAY}
            fi
        fi
    elif [ -f /etc/default-routes ]; then
        while read spec; do
            /sbin/ip route add $spec
        done < /etc/default-routes
        rm -f /etc/default-routes
    fi
}

is_wireless_device ()
{
    [ -x /usr/sbin/iw ] || return 1
    LC_ALL=C /usr/sbin/iw dev $1 info > /dev/null 2>&1 && return 0
    return 1
}

phy_wireless_device ()
{
    cat /sys/class/net/$1/phy80211/name
}

bond_master_exists ()
{
    local bond_name
    [ -z "${1}" ] && return 1
    [ ! -f /sys/class/net/bonding_masters ] && return 1

    for bond_name in $(< /sys/class/net/bonding_masters); do
        [ "${bond_name}" == "${1}" ] && return 0
    done
    return 1
}

install_bonding_driver ()
{
    local fn="install_bonding_driver"

    if ! bond_master_exists ${1}; then
        modprobe bonding || return 1
        echo "+$1" > /sys/class/net/bonding_masters 2>/dev/null
    fi
    (
        # Set config here
        need_config "$1"
        source_config
        if [ -f /sys/class/net/${DEVICE}/bonding/slaves ] && [ $(wc -l < /sys/class/net/${DEVICE}/bonding/slaves) -eq 0 ]; then
            /sbin/ip link set dev ${DEVICE} down

            # parse options and put them to arrays
            for arg in $BONDING_OPTS ; do
                bopts_keys[${#bopts_keys[*]}]=${arg%%=*}
                bopts_vals[${#bopts_vals[*]}]=${arg##*=}
            done

            # add the bits to setup driver parameters here
            # first set mode, miimon
            for idx in $(seq 0 $(( ${#bopts_keys[*]} - 1 ))) ; do
                key=${bopts_keys[$idx]}
                value=${bopts_vals[$idx]}

                if [ "${key}" = "mode" ] ; then
                    echo "${value}" > /sys/class/net/${DEVICE}/bonding/$key || {
                        net_log $"Failed to set value '$value' [mode] to ${DEVICE} bonding device" err $fn
                    }
                    bopts_keys[$idx]=""
                fi
                if [ "${key}" = "miimon" ] ; then
                    echo "${value}" > /sys/class/net/${DEVICE}/bonding/$key || {
                        net_log $"Failed to set value '$value' [miimon] to ${DEVICE} bonding device" err $fn
                    }
                    bopts_keys[$idx]=""
                fi
            done

            # set all other remaining options
            for idx in $(seq 0 $(( ${#bopts_keys[*]} - 1 ))) ; do
                key=${bopts_keys[$idx]}
                value=${bopts_vals[$idx]}

                # option already set; take next
                [[ -z "$key" ]] && continue

                if [ "${key}" = "arp_ip_target" -a "${value:0:1}" != "+" ]; then
                    OLDIFS=$IFS;
                    IFS=',';
                    for arp_ip in $value; do
                        if ! grep -q $arp_ip /sys/class/net/${DEVICE}/bonding/$key; then
                            echo +$arp_ip > /sys/class/net/${DEVICE}/bonding/$key || {
                                net_log $"Failed to set '$arp_ip' value [arp_ip_target] to ${DEVICE} bonding device" err $fn
                            }
                        fi
                    done
                    IFS=$OLDIFS;
                elif [ "${key}" = "arp_ip_target" ]; then
                    if ! grep -q ${value#+} /sys/class/net/${DEVICE}/bonding/$key; then
                        echo "$value" > /sys/class/net/${DEVICE}/bonding/$key || {
                            net_log $"Failed to set '$value' value [arp_ip_target] to ${DEVICE} bonding device" err $fn
                        }
                    fi
                elif [ "${key}" != "primary" ]; then
                    echo $value > /sys/class/net/${DEVICE}/bonding/$key || {
                        net_log $"Failed to set '$value' value [$key] to ${DEVICE} bonding device" err $fn
                    }
                fi
            done
        fi
    )
    return 0
}

is_bonding_device ()
{
    [ -f "/sys/class/net/$1/bonding/slaves" ]
}

# Invoke this when /etc/resolv.conf has changed:
change_resolv_conf ()
{
    oldumask=$(umask)
    umask 022
    s=$(/bin/grep '^[\ \       ]*option' /etc/resolv.conf 2>/dev/null)
    if [ $# -gt 1 ]; then
        if [ "x$s" != "x" ]; then
            s="$s"$'\n'
        fi
        n_args=$#
        while [ $n_args -gt 0 ]; do 
            case "$s" in
            *$1*)
                shift
                n_args=$(($n_args-1))
                continue
                ;;
            esac
            s="$s$1"
            shift
            if [ $# -gt 0 ]; then
                s="$s"$'\n'
            fi
            n_args=$(($n_args-1))
        done             
    elif [ $# -eq 1 ]; then
        if [ "x$s" != "x" ]; then
            s="$s"$'\n'$(/bin/grep -vF "$s" $1)
        else
            s=$(cat $1)
        fi
    fi
    (echo "$s" > /etc/resolv.conf) >/dev/null 2>&1;
    r=$?
    if [ $r -eq 0 ]; then
        [ -x /sbin/restorecon ] && /sbin/restorecon /etc/resolv.conf >/dev/null 2>&1 # reset the correct context
        /usr/bin/logger -p local7.notice -t "NET" -i "$0 : updated /etc/resolv.conf"
        [ -e /run/nscd/socket ] && /usr/sbin/nscd -i hosts # invalidate cache
    fi
    umask "$oldumask"
    return $r
}

# Logging function
#
# Usage: net_log <message> <err|warning|info> <optional file/function name>
#
# Default level is 'err'.

net_log()
{
    local message="$1"
    local level="$2"
    local name="$3"

    [ -z "$message" ] && return 1
    [ -z "$level" ] && level=err
    [ -z "$name" ] && name=$0

    case $level in
    'debug')
        local txt_level=$"DEBUG     "
        ;;
    'err')
        local txt_level=$"ERROR     "
        ;;
    'warning')
        local txt_level=$"WARN      "
        ;;
    'info')
        local txt_level=$"INFO      "
        ;;
    esac

    echo "$txt_level: [$name] $message"

    if [ -x /usr/bin/logger ]; then
        /usr/bin/logger -p daemon.$level -t "$name" "$message"
    fi
    return 0
}

update_DNS_entries()
{
    # Remove duplicate values from DNS options if any:
    if [ -n "${DNS3}" ] && [[ "${DNS3}" == "${DNS2}" || "${DNS3}" == "${DNS1}" ]]; then
        unset DNS3
    fi

    if [ -n "${DNS2}" ] && [[ "${DNS2}" == "${DNS1}" ]]; then
        unset DNS2
    fi

    # Shift the DNS options if necessary:
    if [ -z "${DNS1}" ] && [ -n "${DNS2}" ]; then
        DNS1="${DNS2}"
        unset DNS2
    fi

    if [ -z "${DNS2}" ] && [ -n "${DNS3}" ]; then
        DNS2="${DNS3}"
        unset DNS3
    fi

    # We need to check DNS1 again in case only DNS3 was set at all:
    if [ -z "${DNS1}" ] && [ -n "${DNS2}" ]; then
        DNS1="${DNS2}"
        unset DNS2
    fi
}