Beyond Linux® From Scratch (systemd Edition) - Version 11.0

Chapter 15. Networking Programs

NFS-Utils-2.5.4

Introduction to NFS Utilities

The NFS Utilities package contains the userspace server and client tools necessary to use the kernel's NFS abilities. NFS is a protocol that allows sharing file systems over the network.

This package is known to build and work properly using an LFS-11.0 platform.

Package Information

NFS Utilities Dependencies

Required

libtirpc-1.3.2 and rpcsvc-proto-1.4.2

Optional

Cyrus SASL-2.1.27 (for SASL authentication), LVM2-2.03.13 (libdevmapper for NFSv4 support), libnsl-1.3.0 (for NIS client support), OpenLDAP-2.5.7 (for LDAP authentication), SQLite-3.36.0, MIT Kerberos V5-1.19.2 or libgssapi , and librpcsecgss (for GSS and RPC security support), and libcap-2.53 with PAM

Required (runtime)

rpcbind-1.2.6

User Notes: https://wiki.linuxfromscratch.org/blfs/wiki/nfs-utils

Kernel Configuration

Enable the following options in the kernel configuration (choose client and/or server support as appropriate) and recompile the kernel if necessary: 

File systems  --->
  [*] Network File Systems  --->         [CONFIG_NETWORK_FILESYSTEMS]
    <*/M> NFS client support             [CONFIG_NFS_FS]
    <*/M> NFS server support             [CONFIG_NFSD]

Select the appropriate sub-options that appear when the above options are selected.

[Note]

Note

In BLFS we assume that nfs v3 will be used. If the server offers nfs v4 (for linux, CONFIG_NFSD_V4) then auto-negotiation for v3 will fail and you will need to add nfsver=3 to the mount options. This also applies if that option is enabled in the client's kernel, for example in a distro trying to mount from a BLFS v3 server.

Even if neither end of the connection supports nfs v4, adding nfsver=3 is still beneficial because it prevents an error message "NFS: bad mount option value specified: minorversion=1" being logged on every mount.

Installation of NFS Utilities

Before you compile the program, ensure that the nobody user and nogroup group have been created as done in the current LFS book. You can add them by running the following commands as the root user: 

groupadd -g 99 nogroup &&
useradd -c "Unprivileged Nobody" -d /dev/null -g nogroup \
    -s /bin/false -u 99 nobody
[Note]

Note

The classic uid and gid values are 65534 which is also -2 when interpreted as a signed 16-bit number. These values impact other files on some filesystems that do not have support for sparse files. The nobody and nogroup values are relatively arbitrary. The impact on a server is nil if the exports file is configured correctly. If it is misconfigured, an ls -l or ps listing will show a uid or gid number of 65534 instead of a name. The client uses nobody only as the user running rpc.statd.

Install NFS Utilities by running the following commands: 

./configure --prefix=/usr          \
            --sysconfdir=/etc      \
            --sbindir=/usr/sbin    \
            --disable-nfsv4        \
            --disable-gss &&
make

This package does not come with a working test suite.

Now, as the root user: 

make install                      &&
chmod u+w,go+r /usr/sbin/mount.nfs    &&
chown nobody.nogroup /var/lib/nfs

Command Explanations

--disable-gss: Disables support for RPCSEC GSS (RPC Security).

chown nobody.nogroup /var/lib/nfs: The rpc.statd program uses the ownership of this directory to set it's UID and GID. This command sets those to unprivileged entries.

Configuring NFS Utilities

Server Configuration

/etc/exports contains the exported directories on NFS servers. Refer to the exports.5 manual page for the syntax of this file. Also refer to the "NFS HowTo" available at http://nfs.sourceforge.net/nfs-howto/ for information on how to configure the servers and clients in a secure manner. For example, for sharing the /home directory over the local network, the following line may be added: 

cat >> /etc/exports << EOF
/home 192.168.0.0/24(rw,subtree_check,anonuid=99,anongid=99)
EOF
[Note]

Note

Be sure to replace the directory, network address. and prefix above to match your network. The only space in the line above should be between the directory and the network address.

Systemd Units

Install the NFSv4 server units included in the blfs-systemd-units-20210819 package to start the server at boot. 

make install-nfsv4-server

If you have disabled NFSv4 support, run the following command as the root user to omit the NFSv4 specific systemd units: 

make install-nfs-server

You can edit the /etc/default/nfs-utils file to change the startup options for NFS daemons. Defaults should be fine for most use cases.

Client Configuration

/etc/fstab contains the directories that are to be mounted on the client. Alternately the partitions can be mounted by using the mount command with the proper options. To mount the /home and /usr partitions, add the following to the /etc/fstab: 

<server-name>:/home  /home nfs   rw,_netdev 0 0
<server-name>:/usr   /usr  nfs   ro,_netdev 0 0

The options which can be used are specified in man 5 nfs . If both the client and server are running recent versions of linux, most of the options will be negotiated (but see the Note above on nfsver=3). You can specify either rw or ro, _netdev if the filesystem is to be automatically mounted at boot, or noauto (and perhaps user) for other filesystems.

If the fileserver is not running a recent version of linux, you may need to specifiy other options.

You may need to enable autofs v4 in your kernel, and add the option comment=systemd.automount. Some machines may need this because systemd tries to mount the external filesystems before the network is up. An alternative is to run mount -a as the root user after the system has started.

Systemd Units
[Note]

Note

The following systemd units are not required if the nfs-server units are installed.

Install the units included in the blfs-systemd-units-20210819 package to start the client services at boot. 

make install-nfs-client

Contents

Installed Programs: exportfs, mountstats, mount.nfs, mount.nfs4 (link to mount.nfs), nfsconf, nfsdclnts, nfsiostat, nfsstat, rpc.mountd, rpc.nfsd, rpc.statd, rpcdebug, showmount, sm-notify, start-statd, umount.nfs (link to mount.nfs), and umount.nfs4 (link to mount.nfs)
Installed Libraries: None
Installed Directories: /var/lib/nfs

Short Descriptions

exportfs

maintains a list of NFS exported file systems

mountstats

displays NFS client per-mount statistics

mount.nfs

is used to mount a network share using NFS

mount.nfs4

is used to mount a network share using NFSv4

nfsconf

can be used to test for and retrieve configuration settings from a range of nfs-utils configuration files

nfsdclnts

prints information about NFS clients

nfsiostat

reports input/output statistics for network filesystems

nfsstat

displays statistics kept about NFS client and server activity

rpc.mountd

implements the NFS mount protocol on an NFS server

rpc.nfsd

implements the user level part of the NFS service on the server

rpc.statd

is used by the NFS file locking service. Run on both sides, client as well as server, when you want file locking enabled

rpcdebug

sets or clears the kernel's NFS client and server debug flags

showmount

displays mount information for an NFS server

sm-notify

is used to send Network Status Monitor reboot messages

start-statd

is a script called by nfsmount when mounting a filesystem with locking enabled, if statd does not appear to be running. It can be customised with whatever flags are appropriate for the site

umount.nfs

is used to unmount a network share using NFS

umount.nfs4

is used to unmount a network share using NFSv4

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