Share folders with NFS and mount them automatically

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$ als gewone gebruiker# als root (of met sudo)

Examendoelen in dit hoofdstuk

Netwerkbestandssystemen met NFS koppelen en ontkoppelen
autofs instellen

Understand NFS and its security

An NFS server exports folders; clients mount them like a local disk. RHEL uses NFSv4 by default (one TCP port: 2049).

By default (sec=sys) the server trusts the UID and GID the client sends. Users need the same UIDs on all systems (or central users from IdM/LDAP).
root_squash (default) maps root on the client to the user nobody, so client root is not root on the share.
For real security use Kerberos (sec=krb5p: authentication and encryption).

24.2

Set up an NFS server

Install nfs-utils, write the exports, start the service and open the firewall.

Install and create the folder to share.

#dnf install -y nfs-utils
#mkdir -p /nfsdata /home/ldap
#echo "shared data" > /nfsdata/readme.txt

Describe the exports.

/etc/exports

/nfsdata    192.168.122.0/24(rw,sync)
/home/ldap  192.168.122.0/24(rw,sync,no_root_squash)

Start the server and open the firewall.

#systemctl enable --now nfs-server
#firewall-cmd --add-service={nfs,mountd,rpc-bind} --permanent
#firewall-cmd --reload

Check the exports.
```
#exportfs -v
#exportfs -ra
```

Export option	Meaning
`rw` / `ro`	Read-write / read-only
`sync`	Write to disk before answering (safe)
`root_squash`	Client root → nobody (default)
`no_root_squash`	Client root stays root (only for trusted clients)
`all_squash`	Every user → nobody

Notitie

mountd and rpc-bind are only needed for NFSv3 and for showmount. Pure NFSv4 needs only the nfs service.

24.3

Mount an NFS share

See what the server offers, then mount it like a disk with type nfs.

#dnf install -y nfs-utils
$showmount -e server1
Export list for server1:
/home/ldap 192.168.122.0/24
/nfsdata   192.168.122.0/24
#mkdir /mnt/data
#mount -t nfs server1:/nfsdata /mnt/data
$findmnt /mnt/data
#umount /mnt/data

Onthoud

With NFSv4 you can also mount the server root and browse: mount server1:/ /mnt shows all exports as folders.

24.4

Mount NFS through fstab

For a share that must always be there, add it to /etc/fstab with _netdev, so it is mounted after the network is up.

/etc/fstab (line)

server1:/nfsdata   /mnt/data   nfs   _netdev,defaults   0 0

#systemctl daemon-reload
#mount -a
$findmnt -t nfs4

Op het werk

Add nofail for shares that are not critical: the system then boots even when the NFS server is down.

24.5

Understand autofs

autofs mounts a share only when someone opens its folder, and unmounts it after some idle minutes. No boot problems when the server is away, and no need to mount many home folders.

The master map (/etc/auto.master or files in /etc/auto.master.d/) names a base folder and a map file.
The map file lists the subfolders (keys) and where they come from.

#dnf install -y autofs
#systemctl enable --now autofs

24.6

Define an indirect autofs mount

An indirect map creates subfolders under a base folder: /shares/data is mounted when someone opens it.

Add a line to the master map.
/etc/auto.master.d/shares.autofs
```
/shares   /etc/auto.shares
```
Create the map: key, mount options, source.
/etc/auto.shares
```
data   -rw   server1:/nfsdata
```

Restart autofs and open the folder.

#systemctl restart autofs
$ls /shares
$ls /shares/data
readme.txt
$findmnt /shares/data

Notitie

The folder /shares/data appears only when you open it (ls /shares can be empty before). Do not create it yourself.

24.7

Use wildcards for home folders

With * as the key and & in the source, one line serves every user: /home/ldap/lisa mounts server1:/home/ldap/lisa.

/etc/auto.master.d/home.autofs

/home/ldap   /etc/auto.home

/etc/auto.home

*   -rw   server1:/home/ldap/&

#systemctl restart autofs
$su - ldapuser1
$pwd
/home/ldap/ldapuser1

Examentip

The classic task: "users from the LDAP/NFS server must get their home folder automatically under /home/ldap" — that is exactly this wildcard map. Check with su - USER and findmnt.

24.8

Use a direct autofs mount

A direct map mounts at a full path anywhere in the file system. In the master map the base is /-.

/etc/auto.master.d/direct.autofs

/-   /etc/auto.direct

/etc/auto.direct

/srv/projects   -rw,soft   server1:/nfsdata

#systemctl restart autofs
$ls /srv/projects

24.9

Remember the main points

The most important facts of this chapter, in short.

NFS shares folders over the network. RHEL uses NFSv4 by default (port 2049).
Server: install nfs-utils, write the share in /etc/exports, run exportfs -r, systemctl enable --now nfs-server, open the services nfs (and mountd, rpc-bind for showmount).
Client: showmount -e SERVER lists shares; mount SERVER:/path /mnt mounts one.
At boot: an fstab line with type nfs and the option _netdev.
autofs mounts shares only when a user opens the folder and unmounts them later.
Master map /etc/auto.master.d/NAME.autofs; the map file lists the keys and shares.
An indirect map mounts under one base folder; a wildcard map (* -rw server:/home/&) works for all user folders; a direct map uses full paths (/-).

24.10

Learn the key terms

The words of this chapter in simple English.

Term	Meaning
NFS	Network File System: share folders between Linux systems.
Export	A folder that the NFS server shares.
/etc/exports	The list of exports and who may use them.
showmount	A tool that lists the exports of a server.
_netdev	An fstab option: wait for the network before mounting.
autofs	A service that mounts shares when they are used.
Master map	The autofs file that points to the map files.
Indirect map	A map with keys under one base folder.
Direct map	A map with full mount paths.
Wildcard map	A map with `*` and `&` that works for many folders.