Mastering NFS on CentOS: From Installation to Autofs Integration

NFS (Network File System) is a kernel‑based file system developed by Sun Microsystems that allows users and programs to access remote files as if they were local, using RPC (Remote Procedure Call) in a client‑server model.

Advantages of NFS include saving local storage space by placing frequently used directories such as /home on a central server, which can be accessed over the network.

NFS Software Packages

software package: nfs-utils   # provides server and client tools (not installed by default on minimal CentOS 8)
related packages: rpcbind (required), tcp_wrappers
kernel module: nfs.ko
ports: 2049 (nfsd), other ports allocated by portmap (111)

NFS service processes:
  rpc.nfsd   – main NFS daemon, manages client access
  rpc.mountd – handles mount/unmount requests and permission checks
  rpc.lockd  – optional, manages file locking
  rpc.statd  – optional, checks file consistency

Configuration files:
  /etc/exports
  /etc/exports.d/*.exports

Export File Syntax

Each line in /etc/exports follows the format: /dir host1(opt1,opt2) host2(opt1,opt2) ... Lines starting with # are comments. Host specifications can be: * – wildcard for all clients

IPv4, IPv6, or FQDN

IP networks in CIDR or netmask notation (e.g., 172.31.0.0/16)

Wildcards for hostnames (e.g., *.example.com)

NIS netgroups (e.g., @group_name)

Common export options (default (ro,sync,root_squash,no_all_squash)): ro / rw – read‑only or read‑write async – asynchronous writes (higher performance, lower safety) sync – synchronous writes (default, safer) root_squash – map remote root to nfsnobody (UID 65534) no_root_squash – keep remote root privileges all_squash – map all remote users to

nfsnobody

no_all_squash

– preserve UID/GID of remote users anonuid / anongid – map anonymous users to specific UID/GID

Example /etc/exports Entries

/myshare server.example.com
/myshare *.example.com
/myshare server?.example.com
/myshare server[0-20].example.com
/myshare 172.25.11.10
/myshare 172.25.0.0/16
/myshare 2000:472:18:b51:c32:a21
/myshare 2000:472:18:b51::/64
/myshare *.example.com 172.25.0.0/16
/myshare desktop.example.com(ro)
/myshare desktop.example.com(ro) server[0-20].example.com(rw)
/myshare diskless.example.com(rw,no_root_squash)

NFS Management Tools

rpcinfo – displays RPC program registrations.

rpcinfo -p               # list local RPC services
rpcinfo -s hostname      # show registered programs on a remote host

exportfs – manages exported file systems.

-v   # show all current NFS exports
-r   # re‑read /etc/exports and apply changes
-a   # list all exports
-au  # stop all exports

showmount – lists NFS shares on a remote host.

# showmount -e hostname

Mounting NFS Shares

Typical mount options (see man 5 nfs) include: fg / bg – foreground or background mount hard / soft – request behavior intr – allow interrupting a hard mount rsize / wsize – max bytes per read/write (default 32768) _netdev – defer mount until network is up vers – NFS protocol version (CentOS 8 defaults to 4.2)

Temporary mount example:

# mount -o rw,nosuid,fg,hard,intr 172.31.0.8:/testdir /mnt/nfs/

Persistent mount via /etc/fstab:

172.16.0.1:/public  /mnt/nfs  nfs  defaults,_netdev 0 0

Integrating Autofs

On the NFS server (CentOS 8) create a user and export its home directory:

# mkdir -pv /data/home
# useradd -d /data/home/user1 -u 2000 user1
# echo "/data/home *(rw)" > /etc/exports.d/test.exports
# exportfs -r

On a client (CentOS 7) configure autofs for relative paths:

# useradd -M -u 2000 user1
# echo "/home /etc/auto.home" >> /etc/auto.master
# echo "* -fstype=nfs,vers=3 172.31.0.8:/data/home/&" > /etc/auto.home
# systemctl restart autofs

Verify the mount:

# su - user1
$ pwd
/home/user1
$ df -T /home/user1

For an absolute‑path autofs setup on another client (CentOS 6):

# useradd -M -u 2000 user1
# echo "/- /etc/auto.home" >> /etc/auto.master
# echo "/home/user1 -fstype=nfs,vers=3 nfsserver:/data/home/user1" > /etc/auto.home
# service autofs restart

After logging in as user1, the home directory is mounted from the NFS server, and df -T confirms the NFS type.