adds nfs start

modules/qualifying/learning_centralized_account_management.md

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+# Centralized account management
+
+Up until now most of the services and servers we installed did not need a lot of user accounts to be shared acrossed devices.
+Once we venture into [NFS](https://en.wikipedia.org/wiki/Network_File_System) it will become quite essential to have some sort of shared *database* to manage users and permissions.
+We'll dive into this from the bottom up so let's create a problem first!
+
+## The problem
+
+To create the problem you'll need at least **three** virtual machines.
+They can be as minimal as you want but I would advise to install one with the tools you like, such as `vim-nox`, `htop`, `zsh` etc and make clones from that one.
+We don't need a graphical environment for this exercise.
+Put the hostnames as follows:
+
+* `nas` for the NFS server
+* `client1` for the first client
+* `client2` for the second client
+
+### The server
+
+Let's install an NFS server on the VM.
+This is very easy to do on Debian.
+The command below is enough have an NFS server up and running.
+
+```bash
+➜  ~ sudo apt install nfs-kernel-server
+Reading package lists... Done
+Building dependency tree... Done
+Reading state information... Done
+nfs-kernel-server is already the newest version (1:1.3.4-6).
+0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
+➜  ~ 
+```
+
+But we need to define *which* folders are shared on the network.
+I created a folder `/home/shared` for all shared files and folders and `chown` it to my *main* user.
+
+```bash
+➜  ~ ls -l /home 
+total 8
+drwxr-xr-x 2 waldek waldek 4096 Sep 15 16:21 shared
+drwxr-xr-x 4 waldek waldek 4096 Sep 15 16:33 waldek
+➜  ~ touch /home/shared/hello
+➜  ~ cat /etc/exports                     
+# /etc/exports: the access control list for filesystems which may be exported
+#		to NFS clients.  See exports(5).
+#
+# Example for NFSv2 and NFSv3:
+# /srv/homes       hostname1(rw,sync,no_subtree_check) hostname2(ro,sync,no_subtree_check)
+#
+# Example for NFSv4:
+# /srv/nfs4        gss/krb5i(rw,sync,fsid=0,crossmnt,no_subtree_check)
+# /srv/nfs4/homes  gss/krb5i(rw,sync,no_subtree_check)
+#
+/home/shared       192.168.122.0/24(rw,sync,no_subtree_check)
+➜  ~ sudo exportfs -ar                    
+➜  ~ 
+```
+
+### The first client
+
+On the client we need to `mount` the network share.
+This is done with `mount -t nfs` and a source and destination.
+Let's observe the *out of the box* behavior.
+
+```bash
+➜  ~ mkdir -p media/nfs                                      
+➜  ~ sudo mount -t nfs 192.168.122.100:/home/shared media/nfs
+mount: /home/waldek/media/nfs: bad option; for several filesystems (e.g. nfs, cifs) you might need a /sbin/mount.<type> helper program.
+➜  ~ 
+```
+
+The command is correct but we're missing the helper program to mount NFS shares.
+This can be installed with the `nfs-common` package.
+
+```bash
+➜  ~ sudo apt install nfs-common                             
+Reading package lists... Done
+Building dependency tree... Done
+Reading state information... Done
+nfs-common is already the newest version (1:1.3.4-6).
+0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
+➜  ~ sudo mount -t nfs 192.168.122.100:/home/shared media/nfs
+➜  ~ ls -l media/nfs 
+total 0
+-rw-r--r-- 1 waldek waldek 0 Sep 15 16:21 hello
+```
+
+Wonderful!
+We can now copy files to this network share from all connected clients.
+Now do the same for the second client.
+It should all work as expected, nothing weird here.
+But what happens when we add more users?
+
+### Creating the conflict