systemd dhclient hook is causing md5sum cmds in inexistent files

[Rafael David Tinoco]

I have discovered this issue by doing investigation for the BUG:

https://bugs.launchpad.net/ubuntu/+bug/1832050

"""
I have reproduced the issue by hand doing:

$ apt-get install isc-dhcp-server
$ modprobe dummy

$ ip link add name dummy0 type dummy
$ ip address add 192.168.1.1/24 dev dummy0
$ ip link set dev dummy0 up

cat <<EOF > /etc/dhcp/dhcpd.conf
default-lease-time 600;
max-lease-time 7200;
authorative;

subnet 192.168.1.0 netmask 255.255.255.0 {
    option subnet-mask 255.255.255.0;
    option broadcast-address 192.168.1.255;
    option ntp-servers 192.168.1.50;
    range 192.168.1.42 192.168.1.100;
}
EOF

$ sed -i 's/INTERFACESv4=""/INTERFACESv4="dummy0"/' /etc/default/isc-dhcp-server

and

$ systemctl restart isc-dhcp-server

$ dhclient dummy0 <- problem happens here
"""

When trying a simple dhclient running on a bridge called "teste":

(c)inaddy@eoanchrony:~/work/sources/ubuntu/chrony/debian/tests$ sudo dhclient teste
md5sum: /run/systemd/resolved.conf.d/isc-dhcp-v4-teste.conf: No such file or directory
md5sum: /run/systemd/resolved.conf.d/isc-dhcp-v6-teste.conf: No such file or directory
md5sum: /run/systemd/resolved.conf.d/isc-dhcp-v4-teste.conf: No such file or directory
md5sum: /run/systemd/resolved.conf.d/isc-dhcp-v6-teste.conf: No such file or directory

The problem is caused by the hook script:

/etc/dhcp/dhclient-enter-hooks.d/resolved

In the following line:

md5sum $statedir/isc-dhcp-v4-$interface.conf $statedir/isc-dhcp-v6-$interface.conf &> $oldstate

I believe commit

+systemd (240-6ubuntu9) eoan; urgency=medium

caused this issue with a patch to file "debian/extra/dhclient-enter-resolved-hook"

[Rafael David Tinoco (rafaeldtinoco)]

Related case:

chrony autopkgtest "time-sources-from-dhcp-servers" fails (produces stderr)
https://bugs.launchpad.net/ubuntu/+bug/1832050