/usr/share/lxc/hooks/dhclient-script is in liblxc-common 3.0.1-0ubuntu1~18.04.2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
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# dhclient-script for Linux. Dan Halbert, March, 1997.
# Updated for Linux 2.[12] by Brian J. Murrell, January 1999.
# No guarantees about this. I'm a novice at the details of Linux
# networking.
# Notes:
# 0. This script is based on the netbsd script supplied with dhcp-970306.
# 1. ifconfig down apparently deletes all relevant routes and flushes
# the arp cache, so this doesn't need to be done explicitly.
# 2. The alias address handling here has not been tested AT ALL.
# I'm just going by the doc of modern Linux ip aliasing, which uses
# notations like eth0:0, eth0:1, for each alias.
# 3. I have to calculate the network address, and calculate the broadcast
# address if it is not supplied. This might be much more easily done
# by the dhclient C code, and passed on.
# 4. TIMEOUT not tested. ping has a flag I don't know, and I'm suspicious
# of the $1 in its args.
# 5. Script refresh in 2017. The aliasing code was too convoluted and needs
# to go away. Migrated DHCPv4 script to ip command from iproute2 suite.
# This is based on Debian script with some tweaks. ifconfig is no longer
# used. Everything is done using ip tool from ip-route2.
# 6. LXC Fork
# Remove hooks and dependency on ifconfig.
# Resolve every paths against the $ROOTFS environment variable.
# 'ip' just looks too weird. Also, we now have unit-tests! Those unit-tests
# overwirte this line to use a fake ip-echo tool. It's also convenient
# if your system holds ip tool in a non-standard location.
ip=/sbin/ip
# update /etc/resolv.conf based on received values
# This updated version mostly follows Debian script by Andrew Pollock et al.
make_resolv_conf() {
local resolv_conf="${ROOTFS}/etc/resolv.conf"
local new_resolv_conf="${ROOTFS}/etc/resolv.conf.dhclient-new"
# DHCPv4
if [ -n "$new_domain_search" ] || [ -n "$new_domain_name" ] ||
[ -n "$new_domain_name_servers" ]; then
rm -f $new_resolv_conf
if [ -n "$new_domain_name" ]; then
echo domain ${new_domain_name%% *} >>$new_resolv_conf
fi
if [ -n "$new_domain_search" ]; then
if [ -n "$new_domain_name" ]; then
domain_in_search_list=""
for domain in $new_domain_search; do
if [ "$domain" = "${new_domain_name}" ] ||
[ "$domain" = "${new_domain_name}." ]; then
domain_in_search_list="Yes"
fi
done
if [ -z "$domain_in_search_list" ]; then
new_domain_search="$new_domain_name $new_domain_search"
fi
fi
echo "search ${new_domain_search}" >> $new_resolv_conf
elif [ -n "$new_domain_name" ]; then
echo "search ${new_domain_name}" >> $new_resolv_conf
fi
if [ -n "$new_domain_name_servers" ]; then
for nameserver in $new_domain_name_servers; do
echo nameserver $nameserver >>$new_resolv_conf
done
else # keep 'old' nameservers
sed -n /^\w*[Nn][Aa][Mm][Ee][Ss][Ee][Rr][Vv][Ee][Rr]/p $resolv_conf >>$new_resolv_conf
fi
if [ -f "$resolv_conf" ]; then
chown --reference=$resolv_conf $new_resolv_conf
chmod --reference=$resolv_conf $new_resolv_conf
fi
mv -f $new_resolv_conf $resolv_conf
# DHCPv6
elif [ -n "$new_dhcp6_domain_search" ] || [ -n "$new_dhcp6_name_servers" ]; then
rm -f $new_resolv_conf
if [ -n "$new_dhcp6_domain_search" ]; then
echo "search ${new_dhcp6_domain_search}" >> $new_resolv_conf
fi
if [ -n "$new_dhcp6_name_servers" ]; then
for nameserver in $new_dhcp6_name_servers; do
# append %interface to link-local-address nameservers
if [ "${nameserver##fe80::}" != "$nameserver" ] ||
[ "${nameserver##FE80::}" != "$nameserver" ]; then
nameserver="${nameserver}%${interface}"
fi
echo nameserver $nameserver >>$new_resolv_conf
done
else # keep 'old' nameservers
sed -n /^\w*[Nn][Aa][Mm][Ee][Ss][Ee][Rr][Vv][Ee][Rr]/p $resolv_conf >>$new_resolv_conf
fi
if [ -f "$resolv_conf" ]; then
chown --reference=$resolv_conf $new_resolv_conf
chmod --reference=$resolv_conf $new_resolv_conf
fi
mv -f $new_resolv_conf $resolv_conf
fi
}
# set host name
set_hostname() {
local current_hostname
if [ -n "$new_host_name" ]; then
current_hostname=$(hostname)
# current host name is empty, '(none)' or 'localhost' or differs from new one from DHCP
if [ -z "$current_hostname" ] ||
[ "$current_hostname" = '(none)' ] ||
[ "$current_hostname" = 'localhost' ] ||
[ "$current_hostname" = "$old_host_name" ]; then
if [ "$new_host_name" != "$old_host_name" ]; then
hostname "$new_host_name"
fi
fi
fi
}
# Execute the operation
case "$reason" in
### DHCPv4 Handlers
MEDIUM|ARPCHECK|ARPSEND)
# Do nothing
;;
PREINIT)
# The DHCP client is requesting that an interface be
# configured as required in order to send packets prior to
# receiving an actual address. - dhclient-script(8)
# ensure interface is up
${ip} link set dev ${interface} up
if [ -n "$alias_ip_address" ]; then
# flush alias IP from interface
${ip} -4 addr flush dev ${interface} label ${interface}:0
fi
;;
BOUND|RENEW|REBIND|REBOOT)
set_hostname
if [ -n "$old_ip_address" ] && [ -n "$alias_ip_address" ] &&
[ "$alias_ip_address" != "$old_ip_address" ]; then
# alias IP may have changed => flush it
${ip} -4 addr flush dev ${interface} label ${interface}:0
fi
if [ -n "$old_ip_address" ] &&
[ "$old_ip_address" != "$new_ip_address" ]; then
# leased IP has changed => flush it
${ip} -4 addr flush dev ${interface} label ${interface}
fi
if [ -z "$old_ip_address" ] ||
[ "$old_ip_address" != "$new_ip_address" ] ||
[ "$reason" = "BOUND" ] || [ "$reason" = "REBOOT" ]; then
# new IP has been leased or leased IP changed => set it
${ip} -4 addr add ${new_ip_address}${new_subnet_mask:+/$new_subnet_mask} \
${new_broadcast_address:+broadcast $new_broadcast_address} \
dev ${interface} label ${interface}
if [ -n "$new_interface_mtu" ]; then
# set MTU
${ip} link set dev ${interface} mtu ${new_interface_mtu}
fi
# if we have $new_rfc3442_classless_static_routes then we have to
# ignore $new_routers entirely
if [ ! "$new_rfc3442_classless_static_routes" ]; then
# set if_metric if IF_METRIC is set or there's more than one router
if_metric="$IF_METRIC"
if [ "${new_routers%% *}" != "${new_routers}" ]; then
if_metric=${if_metric:-1}
fi
for router in $new_routers; do
if [ "$new_subnet_mask" = "255.255.255.255" ]; then
# point-to-point connection => set explicit route
${ip} -4 route add ${router} dev $interface >/dev/null 2>&1
fi
# set default route
${ip} -4 route add default via ${router} dev ${interface} \
${if_metric:+metric $if_metric} >/dev/null 2>&1
if [ -n "$if_metric" ]; then
if_metric=$((if_metric+1))
fi
done
fi
fi
if [ -n "$alias_ip_address" ] &&
[ "$new_ip_address" != "$alias_ip_address" ]; then
# separate alias IP given, which may have changed
# => flush it, set it & add host route to it
${ip} -4 addr flush dev ${interface} label ${interface}:0
${ip} -4 addr add ${alias_ip_address}${alias_subnet_mask:+/$alias_subnet_mask} \
dev ${interface} label ${interface}:0
${ip} -4 route add ${alias_ip_address} dev ${interface} >/dev/null 2>&1
fi
# update /etc/resolv.conf
make_resolv_conf
;;
EXPIRE|FAIL|RELEASE|STOP)
if [ -n "$alias_ip_address" ]; then
# flush alias IP
${ip} -4 addr flush dev ${interface} label ${interface}:0
fi
if [ -n "$old_ip_address" ]; then
# flush leased IP
${ip} -4 addr flush dev ${interface} label ${interface}
fi
if [ -n "$alias_ip_address" ]; then
# alias IP given => set it & add host route to it
${ip} -4 addr add ${alias_ip_address}${alias_subnet_mask:+/$alias_subnet_mask} \
dev ${interface} label ${interface}:0
${ip} -4 route add ${alias_ip_address} dev ${interface} >/dev/null 2>&1
fi
;;
TIMEOUT)
if [ -n "$alias_ip_address" ]; then
# flush alias IP
${ip} -4 addr flush dev ${interface} label ${interface}:0
fi
# set IP from recorded lease
${ip} -4 addr add ${new_ip_address}${new_subnet_mask:+/$new_subnet_mask} \
${new_broadcast_address:+broadcast $new_broadcast_address} \
dev ${interface} label ${interface}
if [ -n "$new_interface_mtu" ]; then
# set MTU
${ip} link set dev ${interface} mtu ${new_interface_mtu}
fi
# if there is no router recorded in the lease or the 1st router answers pings
if [ -z "$new_routers" ] || ping -q -c 1 "${new_routers%% *}"; then
# if we have $new_rfc3442_classless_static_routes then we have to
# ignore $new_routers entirely
if [ ! "$new_rfc3442_classless_static_routes" ]; then
if [ -n "$alias_ip_address" ] &&
[ "$new_ip_address" != "$alias_ip_address" ]; then
# separate alias IP given => set up the alias IP & add host route to it
${ip} -4 addr add \
${alias_ip_address}${alias_subnet_mask:+/$alias_subnet_mask} \
dev ${interface} label ${interface}:0
${ip} -4 route add ${alias_ip_address} dev ${interface} >/dev/null 2>&1
fi
# set if_metric if IF_METRIC is set or there's more than one router
if_metric="$IF_METRIC"
if [ "${new_routers%% *}" != "${new_routers}" ]; then
if_metric=${if_metric:-1}
fi
# set default route
for router in $new_routers; do
${ip} -4 route add default via ${router} dev ${interface} \
${if_metric:+metric $if_metric} >/dev/null 2>&1
if [ -n "$if_metric" ]; then
if_metric=$((if_metric+1))
fi
done
fi
# update /etc/resolv.conf
make_resolv_conf
else
# flush all IPs from interface
${ip} -4 addr flush dev ${interface}
exit 2
fi
;;
### DHCPv6 Handlers
# TODO handle prefix change: ?based on ${old_ip6_prefix} and ${new_ip6_prefix}?
PREINIT6)
# ensure interface is up
${ip} link set ${interface} up
# We need to give the kernel some time to active interface
interface_up_wait_time=5
for i in $(seq 0 ${interface_up_wait_time})
do
${ip} addr show ${interface} | grep NO-CARRIER >/dev/null 2>&1
if [ $? -ne 0 ]; then
break;
fi
sleep 1
done
# flush any stale global permanent IPs from interface
${ip} -6 addr flush dev ${interface} scope global permanent
# Wait for duplicate address detection for this interface if the
# --dad-wait-time parameter has been specified and is greater than
# zero.
if [ ${dad_wait_time} -gt 0 ]; then
# Check if any IPv6 address on this interface is marked as
# tentative.
${ip} addr show ${interface} | grep inet6 | grep tentative \
&> /dev/null
if [ $? -eq 0 ]; then
# Wait for duplicate address detection to complete or for
# the timeout specified as --dad-wait-time.
for i in $(seq 0 $dad_wait_time)
do
# We're going to poll for the tentative flag every second.
sleep 1
${ip} addr show ${interface} | grep inet6 | grep tentative \
&> /dev/null
if [ $? -ne 0 ]; then
break;
fi
done
fi
fi
;;
BOUND6|RENEW6|REBIND6)
if [ "${new_ip6_address}" ] && [ "${new_ip6_prefixlen}" ]; then
# set leased IP
${ip} -6 addr add ${new_ip6_address}/${new_ip6_prefixlen} \
dev ${interface} scope global
fi
# update /etc/resolv.conf
if [ "${reason}" = BOUND6 ] ||
[ "${new_dhcp6_name_servers}" != "${old_dhcp6_name_servers}" ] ||
[ "${new_dhcp6_domain_search}" != "${old_dhcp6_domain_search}" ]; then
make_resolv_conf
fi
;;
DEPREF6)
if [ -z "${cur_ip6_prefixlen}" ]; then
exit 2
fi
# set preferred lifetime of leased IP to 0
${ip} -6 addr change ${cur_ip6_address}/${cur_ip6_prefixlen} \
dev ${interface} scope global preferred_lft 0
;;
EXPIRE6|RELEASE6|STOP6)
if [ -z "${old_ip6_address}" ] || [ -z "${old_ip6_prefixlen}" ]; then
exit 2
fi
# delete leased IP
${ip} -6 addr del ${old_ip6_address}/${old_ip6_prefixlen} \
dev ${interface}
;;
esac
exit 0
|