NFS

Global configuration options are set in /etc/nfs.conf. Users of simple configurations should not need to edit this file.

The NFS server needs a list of exports (see exports(5) for details) which are defined in /etc/exports or /etc/exports.d/*.exports. These shares are relative to the so-called NFS root. A good security practice is to define a NFS root in a discrete directory tree which will keep users limited to that mount point. Bind mounts are used to link the share mount point to the actual directory elsewhere on the filesystem.

Consider this following example wherein:

1. The NFS root is /srv/nfs.
2. The export is /srv/nfs/music via a bind mount to the actual target .

# mkdir -p /srv/nfs/music /mnt/music
# mount --bind /mnt/music /srv/nfs/music

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

Add directories to be shared and limit them to a range of addresses via a CIDR or hostname(s) of client machines that will be allowed to mount them in /etc/exports, e.g.:

It should be noted that modifying /etc/exports while the server is running will require a re-export for changes to take effect:

# exportfs -arv

To view the current loaded exports state in more detail, use:

# exportfs -v

For more information about all available options see exports(5).

Start and enable .

By default, starting will listen for connections on all network interfaces, regardless of /etc/exports. This can be changed by defining which IPs and/or hostnames to listen on.

Restart to apply the changes immediately.

To enable access through a firewall, TCP and UDP ports , , and 20048 may need to be opened when using the default configuration; use to examine the exact ports in use on the server:

When using NFSv4, make sure TCP port is open. No other port opening should be required:

When using an older NFS version, make sure other ports are open:

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

To have this configuration load on every system start, edit 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

The previous commands can be saved by executing:

# iptables-save > /etc/iptables/iptables.rules

If using NFSv3 and the above listed static ports for and the following ports may also need to be added to the configuration:

To apply changes, Restart iptables.service.

The NFSv4 protocol represents the local system's UID and GID values on the wire as strings of the form . The process of translating from UID to string and string to UID is referred to as ID mapping. See for details.

Even though idmapd may be running, it may not be fully enabled. If or returns on a client/server, enable it by:

On the client:

# echo N > /sys/module/nfs/parameters/nfs4_disable_idmapping

On the server:

# echo N > /sys/module/nfsd/parameters/nfs4_disable_idmapping

Set as module option to make this change permanent, i.e.:

/etc/modprobe.d/nfsd.conf

options nfs nfs4_disable_idmapping=0
options nfsd nfs4_disable_idmapping=0

To fully use idmapping, make sure the domain is configured in /etc/idmapd.conf on both the server and the client:

See for details.

Users intending to use NFS4 with Kerberos need to start and enable .

For NFSv3 use this command to show the server's exported file systems:

$ showmount -e servername

For NFSv4 mount the root NFS directory and look around for available mounts:

# mount servername:/ /mountpoint/on/client

Then mount omitting the server's NFS export root:

# mount -t nfs -o vers=4 servername:/music /mountpoint/on/client

If mount fails try including the server's export root (required for Debian/RHEL/SLES, some distributions need instead of ):

# mount -t nfs -o vers=4 servername:/srv/nfs/music /mountpoint/on/client

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

Some additional mount options to consider:

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. By default, if these options are not specified, the client and server negotiate the largest values they can both support (see for details). After changing these values, it is recommended to test the performance (see #Performance tuning).

soft or hard

Determines the recovery behaviour of the NFS client after an NFS request times out. If neither option is specified (or if the option is specified), NFS requests are retried indefinitely. If the option is specified, then the NFS client fails a NFS request after retrans retransmissions have been sent, causing the NFS client to return an error to the calling application.

timeo

The value is the amount of time, in tenths of a second, to wait before resending a transmission after an RPC timeout. The default value for NFS over TCP is 600 (60 seconds). 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 stability can be achieved by increasing this timeout value.

retrans

The number of times the NFS client retries a request before it attempts further recovery action. If the option is not specified, the NFS client tries each request three times. The NFS client generates a "server not responding" message after retrans retries, then attempts further recovery (depending on whether the hard mount option is in effect).

_netdev

The option tells the system to wait until the network is up before trying to mount the share - systemd assumes this for NFS.

Another method is using the x-systemd.automount option which mounts the filesystem upon access:

/etc/fstab

servername:/home   ''/mountpoint/on/client''  nfs  _netdev,noauto,x-systemd.automount,x-systemd.mount-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0

To make systemd aware of the changes to fstab, reload systemd and restart .

Create a new file inside , e.g. mnt-home.mount. See for details.

path to share

path to mount the share

Options= share mounting options

To use mnt-home.mount, start the unit and enable it to run on system boot.

To automatically mount a share, one may use the following automount unit:

Disable/stop the mnt-home.mount unit, and enable/start to automount the share when the mount path is being accessed.

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.

When using NFS on a network with a significant number of clients one may increase the default NFS threads from 8 to 16 or even a higher, depending on the server/network requirements:

/etc/nfs.conf

[nfsd]
threads=16

It may be necessary to tune the rsize and wsize mount options to meet the requirements of the network configuration.

In recent linux kernels (>2.6.18) the size of I/O operations allowed by the NFS server (default max block size) varies depending on RAM size, with a maximum of 1M (1048576 bytes), the max block size of the server will be used even if nfs clients requires bigger rsize and wsize. See https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/5/html/5.8_technical_notes/known_issues-kernel It is possible to change the default max block size allowed by the server by writing to the before starting nfsd. For example, the following command restores the previous default iosize of 32k:

# echo 32768 > /proc/fs/nfsd/max_block_size

To make the change permanent, create a systemd-tmpfile:

To mount with the increased rsize and wsize mount options:

# mount -t nfs -o rsize=32768,wsize=32768,vers=4 servername:/srv/nfs/music /mountpoint/on/client

Furthermore, despite the violation of NFS protocol, setting instead of or may potentially achieve a significant performance gain especially on spinning disks. Configure exports with this option and then execute to apply.

This trick is useful for NFS-shares on a wireless network and/or on a network that may be unreliable. If the NFS host becomes unreachable, the NFS share will be unmounted to hopefully prevent system hangs when using the mount option .

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

Create the auto_share script that will be used by cron or systemd/Timers to use ICMP ping to check if the NFS host is reachable:

Make sure the script is executable.

Next check configure the script to run every X, in the examples below this is every minute.

Finally, enable and start .

NetworkManager can also be configured to run a script on network status change.

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

# ln -s /usr/local/bin/auto_share /etc/NetworkManager/dispatcher.d/30-nfs.sh

However, in that particular case unmounting will happen only after the network connection has already been disabled, which is unclean and may result in effects like freezing of KDE Plasma applets.

The following script safely unmounts the NFS shares before the relevant network connection is disabled by listening for the , and vpn-pre-down events, make sure the script is executable:

Create a symlink inside to catch the events:

# ln -s /etc/NetworkManager/dispatcher.d/30-nfs.sh /etc/NetworkManager/dispatcher.d/pre-down.d/30-nfs.sh