# NFSv4 with Kerberos on Debian from scratch

This document will (hopefully) allow you to setup a kerberized NFSv4 server on Debian 11/Ubuntu 22.04.

> Copyright (C) 2022 Bruno Raoult ("br")
> Licensed under the GNU Free Documentation License v1.3 or later.
> Some rights reserved. See COPYING.
>
> You should have received a copy of the GNU Free Documentation License along with this document.
> If not, see [this page](https://www.gnu.org/licenses/fdl-1.3-standalone.html).
>
> SPDX-License-Identifier: [GFDL-1.3-or-later](https://spdx.org/licenses/GFDL-1.3-or-later.html)

foo

## Introduction
### dd
If you share some files between your machines, your choice was probably [SMB/CIFS](https://en.wikipedia.org/wiki/Server_Message_Block),
as it is supported on nearly any platform (GNU/Linux, MacOS, Windows, iOS, Android,
...).

However, there are some limitations that you may find unacceptable: the loss of uid/gid/permissions and the lack of symbolic/hard links for `SMB`.

Another option (at least on GNU/Linux) could be [SSHFS](https://github.com/libfuse/sshfs): It is simple to use,
and requires no special settings but an ssh access to server. It could be the
ideal sharing system for many people.

What I dislike here is the need for an `ssh` access. No, I don't plan to give an ssh access to **my** servers ;-)

This document is about a third solution : NFSv4 coupled with Kerberos
security, on a [[https://www.debian.org/][Debian]] based system (Debian, [[https://ubuntu.com/][Ubuntu]], etc...).

* Pre-requisites
- NTP :: All machines (clients and servers) must be time-synchronized, as Kerberos authentication is partly based on tickets timestamps.
- DNS server (optional) :: Kerberos may, in some configurations make use of some DNS records such as [[https://en.wikipedia.org/wiki/SRV_record][SRV]] or [[https://en.wikipedia.org/wiki/TXT_record][TXT]].
  A lightweight DNS server like [[https://dnsmasq.org/][dnsmasq]] is sufficient, and will avoid the administration of a full-fledged server such as [[https://www.isc.org/bind/][bind]].

* Kerberos (V5)
There are basically two major implementations of [[https://datatracker.ietf.org/doc/html/rfc4120][Kerberos v5]] on GNU/Linux: The original [[http://web.mit.edu/kerberos/www/][MIT]] one, and the [[https://github.com/heimdal/heimdal][Heimdal]] one. There was also a GNU implementation ([[http://www.gnu.org/software/shishi/][Shishi]]), but developement looks stalled for 10+ years.

It appears that the MIT implementation may have some [[https://web.mit.edu/kerberos/dist/index.html][export restrictions]] due to U.S. regulation. Heimdal implementation (explicitely developed outside the USA, in Sweden) does not suffer such limitations. We will therefore use the "/un-regulated/" implementation.

** Naming
We will use the following conventions :
#+CAPTION: Table 1: Local names
| Name                  | Value           | Comment                         |
|-----------------------+-----------------+---------------------------------|
| Kerberos realm        | =LAN=           | Always capital                  |
| Local DNS name        | =lan=           | Typical hostname: machine.lan   |
| Kerberos KDC 1        | =kdc1.lan=      | Primary Key Distribution Center |
| Kerberos KDC 2        | =kdc2.lan=      | Secondary KDC                   |
| Kerberos admin server | =kadmin.lan=    | Administrative server           |
| Kerberos client 1     | =kclient1.lan=  | Test client 1                   |
| Kerberos client 2     | =kclient2.lan=  | Test client 2                   |
| Kerberos credentials  | =krb5/password= | Kerberos admin login/password   |

** Packages installation
On server side, install the necessary packages with :
#+BEGIN_SRC sh
$ sudo apt install krb5-config heimdal-kdc heimdal-servers heimdal-clients heimdal-kcm
#+END_SRC
And on client(s), install the following :
#+BEGIN_SRC sh
$ sudo apt-get install krb5-config heimdal-clients
#+END_SRC
On your desktop, you may also want to install some documentation with:
#+BEGIN_SRC
$ sudo apt-get install heimdal-docs
#+END_SRC
The above package does not include "real" heimdal docs, I did not find it on Ubuntu 22.04 repositories. I managed to install full html documentation with :
#+BEGIN_SRC
git clone https://github.com/heimdal/heimdal.git
cd heimdal
autoreconf -f -i
sh autogen.sh
./configure
make html
cd doc/heimdal.html
sudo cp -ar heimdal.html /usr/share/doc/heimdal-docs/
#+END_SRC

The ~krb5-config~ package installation will ask you some questions, just fill with the information from Table 1 :
- Default Kerberos version 5 realm: ~LAN~
- Kerberos servers for your realm: ~kdc1.lan kdc2.lan~
- Administrative server for your Kerberos realm: ~kadmin.lan~

After this initial configutation, ~/etc/krb5.conf~ should contain something like :
#+BEGIN_SRC conf
[libdefaults]
	default_realm = LAN
	kdc_timesync = true
	forwardable = true
	proxiable = true

[realms]
	LAN = {
		kdc = kdc1.lan
		kdc = kdc2.lan
		admin_server = kadmin.lan
	}

[domain_realm]
    lan  = LAN
	.lan = LAN
#+END_SRC

** test
#+BEGIN_SRC conf
[libdefaults]
	default_realm = LAN
[realms]
	LAN = {
		kdc = kdc1.lan
		kdc = kdc2.lan
		admin_server = kadmin.lan
	}
#+END_SRC

** Server side
*** Heimdal Kerberos installation
** Client side
heimdal-docs heimdal-clients
** Testing
* NFSv4
** Server side
** Client side
** Testing
#+BEGIN_VERSE
zobi zoba
titi toto
* Sources
Kerberos setup:
- ~heimdal-docs~ package documentation : run ~$ info heimdal~
- [[http://chschneider.eu/linux/server/heimdal.shtml][Heimdal setup on Debian]]
- [[http://www.cs.rug.nl/~jurjen/ApprenticesNotes/ad_kinit.html][Debian/Ubuntu Linux with Active Directory Kerberos Server]]
- [[https://web.mit.edu/kerberos/krb5-1.13/doc/admin/princ_dns.html][Principal names and DNS]]
- [[https://www.atlantic.net/dedicated-server-hosting/how-to-setup-kerberos-server-and-client-on-ubuntu-20-04/][Setup (MIT) Kerberos Server and Client on Ubuntu 20.04]]
- [[https://web.mit.edu/kerberos/krb5-1.12/doc/admin/install_kdc.html][MIT Kerberos Documentation: Installing KDCs]]
- [[https://web.mit.edu/kerberos/krb5-1.12/doc/admin/realm_config.html#mapping-hostnames][MIT Kerberos Documentation: Realm configuration decisions]]


--prout
#+END_VERSE
#+CAPTION: and _multiple_
#+CAPTION: lines of *captions*!
#+ATTR_HTML: :class a b
#+ATTR_HTML: :id it :class c d
#+BEGIN_SRC sh
echo "a bash source block with custom html attributes"
#+END_SRC

#+BEGIN_EXPORT html
<style>
.verse-block p { white-space: pre; color: red;}
.verse-block p + p { padding-left: 2em; }
</style>
#+END_EXPORT

#+BEGIN_VERSE
Great clouds overhead
Tiny black birds rise and fall
Snow covers Emacs

---AlexSchroeder
#+END_VERSE