NFS

Summary
Article covers configuration of NFSv4 which is an open standard network file sharing protocol.
Related
NFS Troubleshooting - Dedicated article for common problems and solutions.

From Wikipedia:

Network File System (NFS) is a distributed file system protocol originally developed by Sun Microsystems in 1984, allowing a user on a client computer to access files over a network in a manner similar to how local storage is accessed.

Installation

Both client and server only require the installation of the nfs-utils package.

Note: It is HIGHLY recommended to use a time sync daemon on ALL nodes of your network to keep client/server clocks in sync. Without accurate clocks on all nodes, NFS can introduce unwanted delays! The NTP system is recommended to sync both the server and the clients to the highly accurate NTP servers available on the Internet.

Configuration

Server

ID mapping

Edit /etc/idmapd.conf and set the Domain field to your domain name.

/etc/idmapd.conf

[General]
 
Verbosity = 1
Pipefs-Directory = /var/lib/nfs/rpc_pipefs
Domain = atomic

[Mapping]

Nobody-User = nobody
Nobody-Group = nobody

File system

Note: For security reasons, it is recommended to use an NFS export root which will keep users limited to that mount point only. The following example illustrates this concept.

Define any NFS shares in /etc/exports which are relative to the NFS root. In this example, the NFS root will be /srv/nfs4 and we will be sharing /mnt/music.

# mkdir -p /srv/nfs4/music

Read/Write permissions must be set on the music directory so clients may write to it.

Now mount the actual target share, /mnt/music to the NFS share via the mount command:

# mount --bind /mnt/music /srv/nfs4/music

To make it stick across server reboots, add the bind mount to fstab:

/etc/fstab

/mnt/music /srv/nfs4/music  none   bind   0   0

Exports

Add directories to be shared and an ip address or hostname(s) of client machines that will be allowed to mount them in exports:

/etc/exports

/srv/nfs4/ 192.168.0.1/24(rw,fsid=root,no_subtree_check)
/srv/nfs4/music 192.168.0.1/24(rw,no_subtree_check,nohide) # note the nohide option which is applied to mounted directories on the file system.

Users need-not open the share to the entire subnet; one can specify a single IP address or hostname as well.

For more information about all available options see man 5 exports.

If you modify /etc/exports while the server is running, you must re-export them for changes to take effect:

# exportfs -rav

Starting the server

Start rpc-idmapd and rpc-mountd services. If you want it running at boot time, enable it. Note that these units require other services, which are launched automatically by systemd.

Firewall configuration

To enable access through a firewall, tcp and udp ports 111, 2049, and 20048 need to be opened. To configure this for iptables, edit /etc/iptables/iptables.rules to include the following lines:

/etc/iptables/iptables.rules

-A INPUT -p tcp -m tcp --dport 111 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 2049 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 20048 -j ACCEPT
-A INPUT -p udp -m udp --dport 111 -j ACCEPT
-A INPUT -p udp -m udp --dport 2049 -j ACCEPT
-A INPUT -p udp -m udp --dport 20048 -j ACCEPT

To apply changes, restart iptables service.

Client

Clients need nfs-utils to connect, and to avoid an approx 15 seconds delay with an accompanying error in dmsg that reads, "RPC: AUTH_GSS upcall timed out," users will need to start rpc-gssd service on any client.

Note: NFS4 servers do not need to run this service.

Mounting from Linux

Show the server's exported filesystems:

$ showmount -e servername

Then mount omitting the server's NFS export root:

# mount -t nfs4 servername:/music /mountpoint/on/client

/etc/fstab settings

Using fstab is useful for a server which is always on, and the NFS shares are available whenever the client boots up. Edit /etc/fstab file, and add an appropriate line reflecting the setup. Again, the server's NFS export root is omitted.

/etc/fstab

servername:/music   /mountpoint/on/client   nfs4   rsize=8192,wsize=8192,timeo=14,intr,_netdev	0 0

Note: Consult the NFS and mount man pages for more mount options.

Some additional mount options to consider are include:

rsize and wsize: The rsize value is the number of bytes used when reading from the server. The wsize value is the number of bytes used when writing to the server. The default for both is 1024, but using higher values such as 8192 can improve throughput. This is not universal. It is recommended to test after making this change, see #Performance tuning.

timeo: The timeo value is the amount of time, in tenths of a second, to wait before resending a transmission after an RPC timeout. After the first timeout, the timeout value is doubled for each retry for a maximum of 60 seconds or until a major timeout occurs. If connecting to a slow server or over a busy network, better performance can be achieved by increasing this timeout value.

intr: The intr option allows signals to interrupt the file operation if a major timeout occurs for a hard-mounted share.

_netdev: The _netdev option tells the system to wait until the network is up before trying to mount the share. systemd assumes this for NFS, but anyway it is good practice to use it for all types of networked filesystems

Using autofs

Using autofs is useful when multiple machines want to connect via NFS; they could both be clients as well as servers. The reason this method is preferable over the earlier one is that if the server is switched off, the client will not throw errors about being unable to find NFS shares. See autofs#NFS network mounts for details.

Mounting from Windows

Note: Only the Ultimate and Enterprise editions of Windows 7 and the Enterprise edition of Windows 8 include "Client for NFS".

NFS shares can be mounted from Windows if the "Client for NFS" service is activated (which it is not by default). To install the service go to "Programs and features" in the Control Panel and click on "Turn Windows features on or off". Locate "Services for NFS" and activate it as well as both subservices ("Administrative tools" and "Client for NFS").

Some global options can be set by opening the "Services for Network File System" (locate it with the search box) and right click on client > properties.

Warning: Serious performance issues may occur (it randomly takes 30-60 seconds to display a folder, 2 MB/s file copy speed on gigabit LAN, ...) to which Microsoft does not have a solution yet.[1]

To mount a share using Explorer:

Computer > Map network drive > servername:/srv/nfs4/music

Mounting from OS X

Note: OS X by default uses an insecure (>1024) port to mount a share.

Either export the share with the insecure flag, and mount using Finder:

Go > Connect to Server > nfs://servername/

Or, mount the share using a secure port using the terminal:

# mount -t nfs -o resvport servername:/srv/nfs4 /Volumes/servername

Tips and tricks

Performance tuning

In order to get the most out of NFS, it is necessary to tune the rsize and wsize mount options to meet the requirements of the network configuration.

Automatic mount handling

This trick is useful for laptops that require nfs shares from a local wireless network. If the nfs host becomes unreachable, the nfs share will be unmounted to hopefully prevent system hangs when using the hard mount option. See https://bbs.archlinux.org/viewtopic.php?pid=1260240#p1260240

Make sure that the NFS mount points are correctly indicated in /etc/fstab:

$ cat /etc/fstab

lithium:/mnt/data           /mnt/data	        nfs noauto,noatime,rsize=32768,wsize=32768,intr,hard 0 0
lithium:/var/cache/pacman   /var/cache/pacman	nfs noauto,noatime,rsize=32768,wsize=32768,intr,hard 0 0

The noauto mount option tells systemd not to automatically mount the shares at boot. systemd would otherwise attempt to mount the nfs shares that may or may not exist on the network causing the boot process to appear to stall on a blank screen.

In order to mount NFS share by non-root user user may be required to be added to fstab entry. Also enable rpc-statd.service.

Create the auto_share script that will be used by cron to check if the NFS host is reachable,

/root/bin/auto_share

#!/bin/bash

SERVER="YOUR_NFS_HOST"

MOUNT_POINTS=$(sed -e '/^.*#/d' -e '/^.*:/!d' -e 's/\t/ /g' /etc/fstab | tr -s " " | cut -f2 -d" ")

ping -c 1 "${SERVER}" &>/dev/null

if [ $? -ne 0 ]; then
    # The server could not be reached, unmount the shares
    for umntpnt in ${MOUNT_POINTS}; do
        umount -l -f $umntpnt &>/dev/null
    done
else
    # The server is up, make sure the shares are mounted
    for mntpnt in ${MOUNT_POINTS}; do
        mountpoint -q $mntpnt || mount $mntpnt
    done
fi

# chmod +x /root/bin/auto_share

Create the root cron entry to run auto_share every minute:

# crontab -e

* * * * * /root/bin/auto_share

A systemd unit file can also be used to mount the NFS shares at startup. The unit file is not necessary if NetworkManager is installed and configured on the client system. See #NetworkManger dispatch.

/etc/systemd/system/auto_share.service

[Unit]
Description=NFS automount

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/root/bin/auto_share

[Install]
WantedBy=multi-user.target

Now enable auto_share.

NetworkManger dispatcher

In addition to the method described previously, NetworkManager can also be configured to run a script on network status change.

Enable and start the NetworkManager-dispatcher service.

The easiest method for mount shares on network status change is to just symlink to the auto_share script:

# ln -s /root/bin/auto_share /etc/NetworkManager/dispatcher.d/30_nfs.sh

Or use the following mounting script that checks for network availability:

/etc/NetworkManager/dispatcher.d/30_nfs.sh

#!/bin/bash

SSID="CHANGE_ME"

MOUNT_POINTS=$(sed -e '/^.*#/d' -e '/^.*:/!d' -e 's/\t/ /g' /etc/fstab | tr -s " " | cut -f2 -d" ")

ISNETUP=$(nmcli dev wifi | \grep $SSID | tr -s ' ' | cut -f 10 -d ' ') 2>/dev/null

# echo "$ISNETUP" >> /tmp/nm_dispatch_log

if [[ "$ISNETUP" == "yes" ]]; then
    for mntpnt in ${MOUNT_POINTS}; do
        mountpoint -q $mntpnt || mount $mntpnt
    done
else
    for srvexp in ${MOUNT_POINTS}; do
        umount -l -f $srvexp &>/dev/null
    done
fi

Now when the wireless SSID "CHANGE_ME" goes up or down, the nfs.sh script will be called to mount or unmount the shares as soon as possible.

Configure NFS fixed ports

This article or section is out of date.

Reason: This section was originally refered to NFS version 3. (Discuss)

If you have a port-based firewall, you might want to set up a fixed ports. For rpc.statd and rpc.mountd you should set following settings in /etc/conf.d/nfs-common and /etc/conf.d/nfs-server (ports can be different):

/etc/conf.d/nfs-common

STATD_OPTS="-p 4000 -o 4003"

/etc/conf.d/nfs-server

MOUNTD_OPTS="--no-nfs-version 2 -p 4002"

/etc/modprobe.d/lockd.conf

# Static ports for NFS lockd
options lockd nlm_udpport=4001 nlm_tcpport=4001

After restart nfs-common nfs-server daemons and reload lockd modules you can check used ports with following command:

$ rpcinfo -p

   program vers proto   port  service
    100000    4   tcp    111  portmapper
    100000    3   tcp    111  portmapper
    100000    2   tcp    111  portmapper
    100000    4   udp    111  portmapper
    100000    3   udp    111  portmapper
    100000    2   udp    111  portmapper
    100024    1   udp   4000  status
    100024    1   tcp   4000  status
    100021    1   udp   4001  nlockmgr
    100021    3   udp   4001  nlockmgr
    100021    4   udp   4001  nlockmgr
    100021    1   tcp   4001  nlockmgr
    100021    3   tcp   4001  nlockmgr
    100021    4   tcp   4001  nlockmgr
    100003    2   tcp   2049  nfs
    100003    3   tcp   2049  nfs
    100003    4   tcp   2049  nfs
    100003    2   udp   2049  nfs
    100003    3   udp   2049  nfs
    100003    4   udp   2049  nfs
    100005    3   udp   4002  mountd
    100005    3   tcp   4002  mountd

Then, you need to open the ports 111-2049-4000-4001-4002-4003 TCP and UDP.

Troubleshooting

There is a dedicated article NFS Troubleshooting.

NFS

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