NFS - ArchWiki

# NFS

Related articles

- NFS/Troubleshooting

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 to keep client/server clocks in sync. Without accurate clocks on all nodes, NFS can introduce unwanted delays. The Network Time Protocol daemon 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`.

    /etc/idmapd.conf

    [General]

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

    [Mapping]

    Nobody-User = nobody
    Nobody-Group = nobody

#### Optional configuration

`/etc/conf.d/nfs-server.conf` holds optional configurations for options to pass to rpc.nfsd, rpc.mountd, or rpc.svcgssd. Users setting up a simple configuration may not need to edit this file.

#### 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/ 192.168.1.0/24(rw,fsid=root,no_subtree_check)
    /srv/nfs4/music 192.168.1.0/24(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`.

Note: Modifying `/etc/exports` while the server is running will require a re-export for changes to take effect.

    # exportfs -rav

#### Static ports for NFSv3

Users needing support for NFSv3 clients, may wish to consider using static ports. By default, for NFSv3 operation `rpc.statd` and `lockd` use random ephemeral ports; in order to allow NFSv3 operations through a firewall static ports need to be defined. Edit `/etc/conf.d/nfs-common.conf` to set `STATD_OPTS`:

    /etc/conf.d/nfs-common.conf

    STATD_OPTS="-p 32765 -o 32766 -T 32803"

The `rpc.mountd` should consult `/etc/services` and bind to the same static port 20048 under normal operation; however, if it needs to be explicity defined edit `/etc/conf.d/nfs-server.conf` to set `MOUNTD_OPTS`:

    /etc/conf.d/nfs-server.conf

    MOUNTD_OPTS="-p 20048"

After making these changes, several services need to be restarted; the first writes the configuration options out to `/run/sysconfig/nfs-utils` (see `/usr/lib/systemd/scripts/nfs-utils_env.sh`), the second restarts `rpc.statd` with the new ports, the last reloads `lockd` (kernel module) with the new ports.

    # systemctl restart nfs-config
    # systemctl restart rpcbind
    # systemctl restart rpc-statd
    # systemctl restart nfs-server

After the restarts, use `rpcinfo -p` on the server to examine the static ports are as expected. Using `rpcinfo -p <server IP>` from the client should reveal the exact same static ports.

#### NFSv2 compatibility

Users needing to support clients using NFSv2 (for example U-Boot), should set NFSD_OPTS="-V 2" in /etc/conf.d/nfs-server.conf.

#### Starting the server

Start `rpcbind.service` and `nfs-server.service` using systemd. It is recommended to also enable the service to allow systemd to start it at boot time. Note that this unit requires 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 when using the default configuration; use `rpcinfo -p` to examine the exact ports in use on the server. To configure this for iptables, execute this commands:

    # 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

If you want to have this configuration by default on every system start, you should 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

If you executed the previous commands, you can achieve that by executing

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

Note: this command will override your iptables start configuration with your actual iptables configuration

If using NFSv3 and the above listed static ports for `rpc.statd` and `lockd` these also need to be added to the configuration:

    /etc/iptables/iptables.rules

    -A INPUT -p tcp -m tcp --dport 32765 -j ACCEPT
    -A INPUT -p tcp -m tcp --dport 32803 -j ACCEPT
    -A INPUT -p udp -m udp --dport 32765 -j ACCEPT
    -A INPUT -p udp -m udp --dport 32803 -j ACCEPT

To apply changes, restart `iptables` service.

### Client

Start `rpcbind.service` and `nfs-client.target` using systemd. It is recommended to also enable the target to allow systemd to start it at boot time. Note that this unit requires other services, which are launched automatically by systemd.

#### Manual mounting

Show the server's exported file systems:

    $ showmount -e servername

Then mount omitting the server's NFS export root:

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

If mount fails try including the server's export root (required for Debian/RHEL/SLES, some distributions need `-t nfs4` instead of `-t nfs`):

    # mount -t nfs servername:/full/path/to/music /mountpoint/on/client

Note: Server name needs to be a valid hostname (not just IP address). Otherwise mounting of remote share will hang.

#### Mount using /etc/fstab

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,_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.

_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 file systems

Note: Setting the sixth field (fs_passno) to a nonzero value may lead to unexpected behaviour, e.g. hangs when the systemd automount waits for a check which will never happen.

#### Mount using /etc/fstab with systemd

Another method is using the systemd `automount` service. This is a better option than `_netdev`, because it remounts the network device quickly when the connection is broken and restored. As well, it solves the problem from autofs, see the example below:

    /etc/fstab

    servername:/home   /mountpoint/on/client  nfs  users,noauto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,noatime 0 0

Tip:

- The `noauto` mount option will not mount the NFS share until it is accessed: use `auto` for it to be available immediately.
  If experiencing any issues with the mount failing due to the network not being up/available, enable `NetworkManager-wait-online.service`. It will ensure that `network.target` has all the links available prior to being active.
- The `users` mount option will allow user mounts, but be aware it implies further options as `noexec` for example.

Note: Users trying to automount a NFS-share via systemd which is mounted the same way on the server may experience a freeze when handling larger amounts of data.

#### Mount 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.

## 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.

### Automounting shares with systemd-networkd

Users making use of systemd-networkd might notice nfs mounts the fstab are not mounted when booting; errors like the following are common:

    mount[311]: mount.nfs4: Network is unreachable

The solution is simple; force systemd to wait for the network to be completely configured by running:

    # systemctl enable systemd-networkd-wait-online.service

In theory this slows down the boot-process because less services run in parallel.

### 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 0 0
    lithium:/var/cache/pacman   /var/cache/pacman	nfs noauto,noatime,rsize=32768,wsize=32768 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 shares with non-root users the `user` option has to be added.

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

    /usr/local/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 /usr/local/bin/auto_share

Create the root cron entry to run `auto_share` every minute:

    # crontab -e

    * * * * * /usr/local/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 #NetworkManager dispatcher.

    /etc/systemd/system/auto_share.service

    [Unit]
    Description=NFS automount
    After=syslog.target network.target

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

    [Install]
    WantedBy=multi-user.target

Now enable the `auto_share.service`.

#### NetworkManager 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 /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 `pre-down` and `vpn-pre-down` events:

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

    #!/bin/bash

    # Find your connection UUID with "nmcli con show" in terminal.
    # All NetworkManager connection types are supported: wireless, VPN, wired...
    WANTED_CON_UUID="CHANGE-ME-NOW-9c7eff15-010a-4b1c-a786-9b4efa218ba9"

    if [[ "$CONNECTION_UUID" == "$WANTED_CON_UUID" ]]; then

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

        # or manually list the space-separated mountpoints
        # MOUNT_POINTS="/mnt/nfs_share /mnt/other_nfs_storage"

        # Script parameter $1: NetworkManager connection name, not used
        # Script parameter $2: dispatched event

        case "$2" in
            "up")
                for mntpnt in ${MOUNT_POINTS}; do
                    mountpoint -q $mntpnt || mount $mntpnt
                done
                ;;
            "pre-down");&
            "vpn-pre-down")
                for srvexp in ${MOUNT_POINTS}; do
                    umount -l -f $srvexp >/dev/null
                done
                ;;
        esac
    fi

Make the script executable:

     # chmod +x /etc/NetworkManager/dispatcher.d/30-nfs.sh

and create a symlink inside `/etc/NetworkManager/dispatcher.d/pre-down` to catch the `pre-down` events:

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

The above script can be modified to mount different shares (even other than NFS) for different connections.

See also: NetworkManager#Use dispatcher to handle mounting of CIFS shares.

## Troubleshooting

There is a dedicated article NFS Troubleshooting.

## See also

- See also Avahi, a Zeroconf implementation which allows automatic discovery of NFS shares.
- HOWTO: Diskless network boot NFS root
- NFS Performance Management
- Microsoft Services for Unix NFS Client info
- NFS on Snow Leopard

Categories:

- File systems
- Networking