NFS

2016-06-17T12:58:31Z

Dsafonov:

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:

# vzctl version 3.0.13 or higher (do <code>vzctl --version</code>)
# 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 <code>sysctl -p</code>.

=== 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 <code>kernel.ve_allow_kthreads=1</code> in <code>/etc/sysctl.conf</code>.

RHEL7-based kernels support [https://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-nfs.html three different NFS protocol versions]:
<pre>
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.
</pre>
There are three kernel modules accordingly: <code>nfs</code> (for NFSv2), <code>nfsv3</code>, <code>nfsv4</code>. As [[NFS server inside container]] by this moment supports only NFSv3, it's very likely that you'll need to load <code>nfsv3</code> 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 <code>nfs</code> 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 <code>--features nfs:on</code>, you will need to reboot it.

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

After this you may see nfs in <code>/proc/filesystems</code>
<pre>
# vzctl exec 101 cat /proc/filesystems
ext3
ext2
nodev rpc_pipefs
nodev proc
nodev nfs
nodev sysfs
nodev tmpfs
nodev devpts
</pre>

== Mounting NFS ==
Make sure that packages <code>nfs-utils</code> and <code>nfs-utils-lib</code> or similar are installed in a container. Also make sure that the <code>portmap</code> (or <code>rpcbind</code>) service is started, otherwise the mount with default options will fail and require the <code>-nolock</code> option. See the [[NFS#Known issues|known issues]] for more information.

Assuming that you already have NFS server set up at <code>192.168.0.1:/nfs_pub</code>, mounting will be simple
<pre>
# 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
</pre>

For more details on how to setup NFS mount, see [http://nfs.sourceforge.net/nfs-howto/ar01s04.html 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 <code>portmap</code> before trying to install nfs-common.
** For Ubuntu/Debian OpenVZ containers, the <code>portmap/rpcbind</code> service may not start automatically. However, you can enable it by editing the <code>/etc/default/nfs-common</code> configuration file.

== See also ==
* [http://nfs.sourceforge.net/nfs-howto/ar01s04.html NFS-client HOWTO]

[[Category: HOWTO]]

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