- UsingNfsWithOpenVz

Introduction

This page describes AlexisHuxley's experiences running:

1. an NFS server on an OpenVz VE

2. the automounter on an OpenVz VE

Analysis

To my knowledge there are three NFS implementations for Linux. Each of them exhibits some problems running in an OpenVz virtual machine:

For my own personal use, being able to read and write files of sizes larger than 2GB was essential so I had to go with the unfs3. This meant I had to contend with the following problems:

1. rdiff-backup seems to be one of the few programs needing lchown()

2. when the automounter invokes mount and umount then it wants to write to /etc/mtab, which on a VE is a symlink to a read-only 'file' under /proc; although mount and umount can be told not to write to this file, there is no convenient way to get the automounter to relay this request to them

3. the Debian automounter package suffers from bug whereby the mountpoints are removed as the autmounter exits and they are not recreated when it is next started.

Procedure

1. On the server install the unfs3 package.
2. On the clients install the nfs-common package.

3. On the HN add the following to /etc/modules:

   autofs4
   nfs 

   (The HN may not be the NFS server, so it would not load these modules and VEs don't have the power to load modules.)

4. Ensure all VE clients mount the server with the -nolock option.

5. To work around the disappearing mountpoints edit /etc/init.d/autofs, locate the line:

   : echo LOCALOPTIONS $localoptions 

   and immediately after it add:

   mkdir -p $dir 

6. To get the automounter to invoke mount and umount with the -n option so as to not write to /etc/fstab, run:

   dpkg-divert --add --rename /bin/mount
   dpkg-divert --add --rename /bin/umount
   cat > /bin/mount <<'EOF'
   #!/bin/sh
   if [ "X$MOUNT_MTAB" = Xfalse -a $(/usr/bin/basename $0) = mount ]; then
       exec $0.distrib -n "$@"
   elif [ "X$MOUNT_MTAB" = Xfalse -a $(/usr/bin/basename $0) = umount ]; then
       exec $0.distrib -in "$@"
   else
       exec $0.distrib "$@"
   fi
   EOF
   chmod 755 /bin/mount
   ln -f /bin/mount /bin/umount
   echo "export MOUNT_MTAB=false" >> /etc/default/autofs 

   and restart the automounter.
7. Be sure that the portmapper is started automatically at boot-time on the client and server.

8. To fix rdiff-backup, see GettingRdiffBackupWorkingOnUnfs3.

See also

• Computing

• AlexisHuxley

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CategoryProcedure