Divide the "Service Management" chapter into two sections. The 1st (the
original) explaining General, not NixOS specific ways to interact with
Systemd. The 2nd section, explaining NixOS specific things worth
knowing.
Explain in the 2nd section a bit NixOS modules and services of Nixpkgs,
and mention `systemd.user.services` option. Give an example
demonstrating how to enable imperatively an upstream provided unit file
for a user. Explain why `systemctl --user enable` doesn't work for the
long term on NixOS.
I have a nixops network where I deploy containers using the `container`
backend which uses `nixos-container` intenrally to deploy several
containers to a certain host.
During that time I removed and added new containers and while trying to
deploy those to a different host I realized that it isn't guaranteed
that each container gets the same IP address which is a problem as some
parts of the deployment need to know which container is using which IP
(i.e. to configure port forwarding on the host).
With this change you can specify the container's IP like this (and don't
have to use the arbitrarily used 10.233.0.0/16 subnet):
```
$ nixos-container create test --config-file test-container.nix \
--local-address 10.235.1.2 --host-address 10.235.1.1
```
Nix commands inside the container have been broken since 18.03,
and no fix is yet in sight. Lets remove from the documentation
that this is a usecase that we support, as it doesn't seem
likely that this will be fixed before 18.09 either.
See #40355
Network Manager calls dhclient on container interfaces and fails
which locks you out of the container after a few seconds, unless
you tell it not to manage these interfaces.
* manual: Mark commands that require root
Mark every command that requires to be run as root by prefixing them
with '#' instead of '$'.
* manual: Add note about commands that require root
