Explaination of files under /etc/NetworkManager?

@vanadium provided a general way for investigating files' usage.

1. For each file you're concerned with, dpkg -S filename shows which package provided the file. Directories can also be fed into filename, but a full path to the directory is needed.
2. For each package listed above, dpkg -L package will show all the files installed by the package.

So for files under /etc/NetworkManager

• dispatcher.d

  All execute scripts in this directory or its subdirectories will be executed by NetworkManager in alphabetical order in response to network events. Each script receives two arguments, the first being the interface name of the device an operation just happened on, and second the action. For example, the following script disable offload features of temporary network adapters

  #!/bin/bash
  # file: /etc/NetworkManager/dispatcher.d/80-disable-offload.sh
  # usage: diable offload when eno1/enp0s31f6 is up
  interface=$1
  event=$2
  if [[ $interface == "eno1" || $interface == "enp0s31f6" ]] && [[ $event == "up" ]]; then
    TOE_OPTIONS="rx tx sg tso ufo gso gro lro rxvlan txvlan rxhash"
    for TOE_OPTION in $TOE_OPTIONS; do
        /sbin/ethtool --offload $interface $TOE_OPTION off
    done
  fi
  exit 0
  

• NetworkManager.conf

  The default content on my machine is

  [main]
  plugins=ifupdown,keyfile
  dns=default
  
  [ifupdown]
  managed=false
  
  [device]
  wifi.scan-rand-mac-address=no
  

  where

  • ifupdown is the plugin used on the Debian and Ubuntu distributions, and reads Ethernet and Wi-Fi connections from /etc/network/interfaces.
  • keyfile is the generic plugin that supports all the connection types and capabilities that NetworkManager has. It writes files out in an .ini-style format in /etc/NetworkManager/system-connections.
  • [ifupdown] manage is set to false as default. If set to false, then any interface listed in /etc/network/interfaces will be ignored by NetworkManager. (My question: how can network-manager manager networks as this is set to false?)

• conf.d

  Users can add additional .conf files to this directory because NetworkManager.conf may be erased by a software update.

• system-connections stores information about connections such as wifi. It is managed by keyfile plugin as explained above. These are the connections one edits in nmtui.

• dnsmasq.d and dnsmasq-shared.d

  When the dnsmasq plugin is enabled, files in these two folder controls its behavior. For an example of how to enable it and a simple configuration, see Using the NetworkManager’s DNSMasq plugin.