An NFS Server

Scope: the Unix way — exporting a directory with /etc/exports and exportfs. The export machinery was configured and verified for real; the serving daemon itself is (documented) for the kernel reason given in the README.

The whole config is one file of one-liners

Install: sudo apt install nfs-kernel-server. Then examples/exports:

/srv/nfsshare 127.0.0.1(rw,sync,no_subtree_check,root_squash)

Read it left to right: this directory, offered to this client (an IP, a hostname, a network like 192.168.1.0/24, or *), with these options. No users, no passwords — NFS's trust is the client's address, plus the user IDs it presents (next chapter).

Apply and inspect:

sudo exportfs -ra          # re-export everything in /etc/exports
sudo exportfs -v           # the effective export table

/srv/nfsshare  127.0.0.1(sync,wdelay,hide,no_subtree_check,sec=sys,rw,root_squash,no_all_squash)

exportfs -v is NFS's testparm: it shows the options actually in force, defaults included — root_squash present, wdelay added, and so on. After any exports edit, -ra then -v is the ritual.

The options that matter

Option	Meaning
ro / rw	read-only / read-write (default ro)
sync	reply only after data is truly written (safe; async is faster and risks loss on a crash — know which you're choosing)
root_squash	the client's root user is mapped to nobody on the server (the default, and a good one)
no_root_squash	client root = server root. Almost never what you want; see Security
no_subtree_check	skips a check that mostly matters when exporting a subdirectory of a filesystem; standard on modern setups
all_squash + anonuid	map everyone to one chosen user — the blunt but effective fix for UID mismatches

The daemon, honestly

On a normal Ubuntu server, systemctl start nfs-server (with rpcbind) starts the kernel's NFS service and your exports go live. In this guide's lab, that step is where the sandbox said no: the test kernel had no NFS modules at all (nfs-server stayed inactive, and even showmount couldn't reach an RPC service). The configuration half — file, exportfs, effective table — is verified above; the daemon half is the documented standard procedure. The distinction matters less for NFS than most things: the mortal's NFS work is the exports file and the client mount.