NFS server inside container
There are two ways to setup NFS server on common HN: use a user-space NFS server daemon or use an in-kernel implementation of NFS server. Some peculiarities appear if you intend to run NFS server in container.
|
Note: for information about NFS client inside container, see NFS. |
Contents
Kernel NFS server
Binary RPMs that are provided by OpenVZ community contain kernels compiled
without NFS server support. Thus you have to
recompile the kernel with CONFIG_NFSD=m. After booting in this kernel you'll be able
to use NFS server on HN.
In-kernel NFS server runs kernel threads to service requests of clients.
But for security reasons kernel threads are prohibited in containers! So you won't
be able to run NFS server inside container without patching the kernel.
User-space NFS server
Advantage of user-space NFS server is that it does not require kernel support. Also if it crashes — there is no crash of the system: just one process dies, not the kernel! The disadvantage of user-space NFS server is its productivity: no one can be faster than in-kernel implementation.
One well-known implementation of NFS server is "The LINUX User-Space NFS Server" by Olaf Kirch.
Some Linux distributions contain this package: Debian Sarge (nfs-user-server), OpenSUSE 10.0 (nfs-server).
For other distributions you can download sources (for example from Debian repository) and compile it.
There is a small trick you have to know about running mountd and nfsd (these two daemons and portmap constitute a user-space server). You should run them with the -r option:
# portmap # rpc.mountd -r # rpc.nfsd -r
The reason is that these daemons check the major number of the device where the directory to export resides.
If major equals 0 then daemons assume that it is NFS and don't want to re-export it. Symptoms are
that clients will always get a "permission denied" error. Simfs (the file system on which container is located)
is associated with so called unnamed device, in which major equals 0. So, to prevent daemons from checking for
re-exporting — just use this -r option.
“The LINUX User-Space NFS Server” by Olaf Kirch implements NFSv2. It means that only files with sizes less than 2GB are processed. If you intend to use such big files then you should use another user-space NFS server implementation: unfs3. It implements v3 of NFS protocol standard.
Please note that the user-space NFS server does not provide locking, or at least I couldn't get locking to work - Elronxenu 19:49, 15 November 2007 (EST)
On Debian Lenny
The current stable debian version 5.0 (lenny) provides two packages for user space nfs support: nfs-user-server and unfs3. Here i describe my experiences with them --Strimo 17:47, 16 February 2009 (UTC)
nfs-user-server
aptitude install nfs-user-server
First i used nfs-user-server package since i didn't know unfs3. After installing i always got the permission denied error when i tried to mount any exported path until i found this article. So i patched the /etc/init.d/nfs-user-server file to include the -r parameter by adding -- -r to the start-stop-daemon line responsible for starting rpc.mountd and rpc.nfsd:
start-stop-daemon --start --oknodo --quiet --exec /usr/sbin/rpc.nfsd -- -r
start-stop-daemon --start --oknodo --quiet --exec /usr/sbin/rpc.mountd -- -r
After the modification and a nfs server restart (/etc/init.d/nfs-user-server restart) i was able to mount a nfs share. At first the nfs server seems to work fine but anytime i want to edit any text file (using nano or mcedit) i got strange errors on writing to the file and i never solved the problem nor detected why this happens. So i switched to unfs3 ...
Note: nfsmount from busybox not works with nfs-user-server in Debian Lenny, it write message "rpc failed: 2" when I try boot from nfs server. unfs3 works fine. Such problem into Ubuntu: https://bugs.launchpad.net/ubuntu/+source/nfs-user-server/+bug/189593
unfs3
aptitude install unfs3
Works fine until now. Note that both unfs3 and nfs-user-server do not support file locking!
