NFS

This page describes how to use NFS client inside a container.

Note: see NFS server inside container for info about nfsd. Mounting filesystems from the hardware node can be performed more elegantly using Bind mounts.

Preparations

Prerequisites

You will need the following software:

1. vzctl version 3.0.13 or higher (do vzctl --version)
2. kernel version 2.6.18-028test006 or higher (2.6.18-028stab* will do), or any recent RHEL5-based or 2.6.20-based kernel.

Note: In all the kernels earlier than 028stab038, kernel NFS support can be given to a container by setting:

     sunrpc.ve_allow_rpc = 1
     fs.nfs.ve_allow_nfs = 1
     kernel.ve_allow_kthreads = 1

This can be done by adding the above lines into /etc/sysctl.conf on the hardware node, and then running sysctl -p.

Prepare the HN

For NFS mounts to work in the containers with the RHEL5-based kernels you must enable kernel threads in the container by setting kernel.ve_allow_kthreads=1 in /etc/sysctl.conf.

RHEL7-based kernels support three different NFS protocol versions:

NFS version 2 (NFSv2) is older and is widely supported.
NFS version 3 (NFSv3) has more features, including 64bit file handles, Safe Async writes and more robust error handling.
NFS version 4 (NFSv4) works through firewalls and on the Internet, no longer requires portmapper, supports ACLs, and utilizes stateful operations.
Red Hat Enterprise Linux supports NFSv2, NFSv3, and NFSv4 clients, and when mounting a file system via NFS, Red Hat Enterprise Linux uses NFSv3 by default, if the server supports it.

There are three kernel modules accordingly: nfs (for NFSv2), nfsv3, nfsv4. As NFS server inside container by this moment supports only NFSv3, it's very likely that you'll need to load nfsv3 module for clients.

# modprobe nfs

You will probably want the nfs module to load automatically on reboots. One way to do this is to put the modprobe command in your /etc/rc.d/rc.local file:

 modprobe nfs

Alternatively, you can add a new line with nfs to your /etc/modules or /etc/modules.conf file.

Prepare the container

To allow a container to use NFS filesystem, you will need to start it with "nfs" feature enabled. If the container is running while you set the --features nfs:on, you will need to reboot it.

# vzctl set 101 --features "nfs:on" --save
# vzctl start 101

After this you may see nfs in /proc/filesystems

# vzctl exec 101 cat /proc/filesystems
        ext3
        ext2
nodev   rpc_pipefs
nodev   proc
nodev   nfs
nodev   sysfs
nodev   tmpfs
nodev   devpts

Mounting NFS

Make sure that packages nfs-utils and nfs-utils-lib or similar are installed in a container. Also make sure that the portmap (or rpcbind) service is started, otherwise the mount with default options will fail and require the -nolock option. See the known issues for more information.

Assuming that you already have NFS server set up at 192.168.0.1:/nfs_pub, mounting will be simple

# vzctl enter 100
# mkdir /nfs
# mount -t nfs 192.168.0.1:/nfs_pub /nfs
# cat /proc/mounts 
simfs / simfs rw 0 0
proc /proc proc rw 0 0
sysfs /sys sysfs rw 0 0
devpts /dev/pts devpts rw 0 0
nfs /nfs nfs rw,vers=3,rsize=32768,wsize=32768,hard,proto=tcp,timeo=600,retrans=2,sec=sys,addr=192.168.0.1 0 0

For more details on how to setup NFS mount, see NFS-client HOWTO

Known issues

• There are quite a few parameters in NFS, so sometimes it doesn't work due to misconfiguration. We've created a separate page describing such situations: NFS doesn't work.
• Package nfs-common can not be installed. Make sure you start portmap before trying to install nfs-common.
  • For Ubuntu/Debian OpenVZ containers, the portmap/rpcbind service may not start automatically. However, you can enable it by editing the /etc/default/nfs-common configuration file.

See also

• NFS-client HOWTO