Provide command line option(s) to choose between legacy network and systemd-network

[jkirk]

It would be nice to have an option to let grml-debootstrap set up a legacy network or a systemd-network configuration.

This includes but might not be limited to:

• Enable/disable systemd-networkd and systemd-resolved
• Provide (legacy / systemd) network configuration or copy configuration from host (not sure how to handle a non-systemd host system)
• Choose between classic and predictable interface naming scheme
• Command line option --defaultinterfacenames needs to take into account which network-configuration-option has been chosen

Just for reference, a valid DHCP configuration would look like this (when using the predictable interface names):

# /etc/systemd/network/80-dhcp.network
[Match]
Name=en*

[Network]
DHCP=yes

Proposed command line options:

• --network-legacy (default?)
• --network-systemd
• --network-naming-legacy (default?)
• --network-naming-predictable

[jkirk]

Because of systemd/systemd#5625 the following configuration should be provided:

# /etc/systemd/network/80-dhcp.network
[Match]
Name=en*

[Network]
#DHCP=yes
DHCP=ipv4
IPv6AcceptRA=no
LinkLocalAddressing=no

[jkirk]

In our todays Grml-Meeting we decided to provide the following options with the following behavior:

• --nointerfaces: Do not install network configuration files
• --defaultinterfaces (new default): Install default /etc/network/interfaces or /etc/network/80-dhcp.network (depending on --network <network type>, see below).
• --hostinterfaces (old default): Copy /etc/network/interfaces or /etc/network/* from host to target (depending on --network <network type>, see below).

Some of the functionality is already provided in PR #110.

New configuration option:

• --network <network type>: Either 'ifupdown' (default) or 'systemd'. Choose which default network (see --defaultinterfaces) or host network configuration (see --hostinterfaces) should be deployed and which network manager should be enabled. (The other will be disabled.)

The default systemd networkd configuration, which will be deployed if --network systemd is given, should look like this:

# /etc/systemd/network/80-dhcp.network
[Match]
Name=e*

[Network]
DHCP=yes
#DHCP=ipv4
#IPv6AcceptRA=no
#LinkLocalAddressing=no

Note: We match e* because we also want to match eth* and Predictable network interface names of the type Ethernet

The default ifupdown network configuration, which will be deployed if no --network or if the --network ifupdown option is given:

# /etc/network/interfaces - generated by grml-debootstrap

# Include files from /etc/network/interfaces.d when using
# ifupdown v0.7.44 or newer:
#source-directory /etc/network/interfaces.d

auto lo
iface lo inet loopback

allow-hotplug eth0
iface eth0 inet dhcp

allow-hotplug $PREDICTABLE_INTERFACE
iface $PREDICTABLE_INTERFACE inet dhcp

Note: We only provide eth0 and the detected "predicted interface name". Wildcards are not possible in /etc/network/interfaces.

We also decided to not install / copy any examples anymore. Even if /etc/network/interfaces.examples exists.