# 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 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`.

    /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/ 192.168.1.0/24(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

#### NFSv2 compatibility

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

#### Starting the server

Start `nfs-server.target` using systemd (you may need to update nfs-utils for `nfs-server.target` to work). 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.

#### 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

Start `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.

Clients with a kernel version prior to 3.12.7-2 (the current linux-lts for example) MUST start `rpc-gssd.service` to avoid an approx 15 seconds delay with an accompanying error in dmesg that reads, "RPC: AUTH_GSS upcall timed out" due to a kernel bug.

Note: The server does not need to run this service.
Warning: Starting this service without having it configured properly will result in error messages like:

    rpc.gssd[30473]: ERROR: Key table file '/etc/krb5.keytab' not found while beginning keytab scan for keytab 'FILE:/etc/krb5.keytab'
    rpc.gssd[30473]: ERROR: gssd_refresh_krb5_machine_credential: no usable keytab entry found in keytab /etc/krb5.keytab for connection with host server.domain
    rpc.gssd[30473]: ERROR: No credentials found for connection to server server.domain

and might lock up any NFS mount on the system when mounting and unmounting some mounts very often.

An alternative is to blacklist `rpcsec_gss_krb5` as described on Red Hat's Bugzilla.

    # echo "blacklist rpcsec_gss_krb5" > /etc/modprobe.d/rpcsec_gss_krb5-blacklist.conf
    # reboot

#### Mounting from Linux

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):

    # 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.

##### 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

minorversion
  Use `minorversion=1` for mounting a Windows Server 2012 (Essentials) share with NFS version 4.1

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.

##### 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,hard,intr,noatime 0 0

Tip: `noauto` above will not mount the NFS share until it is accessed: use `auto` for it to be available immediately.
If you have any issues with the mount failing due to the network not being up/available, enable `NetworkManager-wait-online.service`: this will ensure that `network.target` has all the links available prior to being active.
Note: If you try to automount a NFS-share via systemd which is mounted the same way on the server, the system and all applications who try to use the share may freeze when handling larger amounts of data.

##### 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,nolocks,locallocks servername:/srv/nfs4 /Volumes/servername

See https://blogs.oracle.com/jag/entry/nfs_on_snow_leopard for an explanation on why to use the `nolocks` and `locallocks` options.

## 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 #NetworkManager dispatcher.

    /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`.

#### 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 /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.

## 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
- If you are setting up the Arch Linux NFS server for use by Windows clients through Microsoft's SFU, you will save a lot of time and hair-scratching by looking at this forum post first !
- Microsoft Services for Unix NFS Client info
- Unix interoperability and Windows Vista Prerequisites to connect to NFS with Vista

Categories:

- File systems
- Networking