Lesson 5

Date: 2/19/2009
Network File System (NFS)
Linux for Engineering and IT Applications


Practical Exercises with NFSv3

1. Setup your desktop machine as NFS client and your cluster node as NFS server, following the instructions below.

Install the NFS related packages by using apt-get.
On your node: 
apt-get install portmap nfs-common nfs-kernel-server
On the desktop: 
apt-get install portmap nfs-common
On your node, create a directory on top of your home directory to export it, for example, 
mkdir /home/exports
chmod 755 /home/exports
Create a dummy user and create his home directory in /home/exports: 
/usr/sbin/groupadd -g 666 jonny
/usr/sbin/useradd -m -s /bin/bash -u 666 -g 666 -d /home/exports/jonny jonny
Copy some files from /etc into directory /home/exports/jonny and give them ownership "jonny": 
cp /etc/hosts /home/exports/jonny
cp /etc/nsswitch.conf /home/exports/jonny
cp /etc/inetd.conf /home/exports/jonny
Then 
cp /etc/securetty /home/exports/jonny
and live it a root ownreship.
Modify file /etc/exports to include export of directory /home/exports to your desktop, for example, desktop02: 
/home/exports  desktop02(rw)
Make sure your desktop and its IP address are included in /etc/hosts file. Start portmap and NFS services: 
/etc/init.d/portmap start
/etc/init.d/nfs-common start
/etc/init.d/nfs-kernel-server start
Make sure the services are running by executing command rpcinfo: 
rpcinfo -p
You should see the following: 
   program vers proto   port
    100000    2   tcp    111  portmapper
    100000    2   udp    111  portmapper
    100024    1   udp  41642  status
    100024    1   tcp  40680  status
    100003    2   udp   2049  nfs
    100003    3   udp   2049  nfs
    100003    4   udp   2049  nfs
    100021    1   udp  34976  nlockmgr
    100021    3   udp  34976  nlockmgr
    100021    4   udp  34976  nlockmgr
    100003    2   tcp   2049  nfs
    100003    3   tcp   2049  nfs
    100003    4   tcp   2049  nfs
    100021    1   tcp  39350  nlockmgr
    100021    3   tcp  39350  nlockmgr
    100021    4   tcp  39350  nlockmgr
    100005    1   udp  56432  mountd
    100005    1   tcp  57344  mountd
    100005    2   udp  56432  mountd
    100005    2   tcp  57344  mountd
    100005    3   udp  56432  mountd
    100005    3   tcp  57344  mountd

  • On the desktop machine run rpcinfo pointing at the server 
    rpcinfo -p node02
    If you see the same output as on the NFS server, it means the server allows you to access the portmap and its rpc services. Check what directories are exported to you from the server: 
    /sbin/showmount -e node02
    It should show 
    /home/exports desktop02
    Now you are ready to mount its directory on the node. Create a new mounting point and mount the exported directory onto it: 
    mkdir /home/exports
mount node02:/home/exports /home/exports
    To make sure the directory has been mounted, run command 
    df -h
    The mounted directory shows up in the bottom of the file systems list: 
    node02:/home/exports   494M   78M  390M  17% /home/exports
    To see who is the owner of the files in the directory, run command 
    ls -l /home/exports/jonny
    Since there is no user with UID=666 and GID=666 on the node, the mounted directory would belong to a non-existent user: 
    ls -l /home/exports/jonny
total 5
-rw-r--r--    1 666      666           104 Feb 10 19:32 hosts
-rw-r--r--    1 666      666          1750 Feb 10 19:32 nsswitch.conf
-rw-------    1 root     root          114 Feb 10  2003 securetty
-rw-r--r--    1 666      666           289 Feb 10 19:32 inetd.conf
    Create user jonny with UID=GID=667 and try to change the ownership of the directory on the node: 
    chown jonny:jonny /home/exports/jonny
    It doesn't work.

    Change the UID and GID of jonny to be consistent with those on the NFS server: 
    /usr/sbin/groupmod -g 666 jonny
/usr/sbin/usermod -u 666 -g 666 jonny
    Become user jonny then step into directory /home/exports: 
    su jonny
cd /home/exports/jonny
    and see if you can create files in this directory. Unmount the directory, 
    umount /home/exports
    Modify file /etc/fstab by including a new entry with /home/exports: 
    node02:/home/exports  /home/exports   nfs     rw      0    0
    Then run 
    mount -a
    Check if it is mounted 
    df -h
    Remove the entry from /etc/fstab and unmount the directory. If the directory can not get unmounted and you receive error message "device is busy", check what processes hold the directory by executing command fuser: 
    /bin/fuser -m (file_system)
    For example, 
    /bin/fuser -m /home/exports
    Kill these processes and try to unmount the directory again.
    Try to avoid NFS mounting through /etc/fstab. Use either manual mount or automount.

    2. Mount the directory on the desktop again. Shutdown the NFS server on your node: 
    /etc/init.d/nfs-kernel-server stop
    Try to access the NFS mounted directory, for example, with ls.
    Try Ctrl_C to unfreeze the terminal.
    Start the NFS server on you node 
    /etc/init.d/nfs-kernel-server start
    and try to access the directory again.

    3. Repeat exercise #2 using options rw,intr,hard in command mount.

    4. Repeat exercise #2 using options rw,intr,soft in command mount. Wait for 30 - 60 seconds until it times out.

    5. Observing stale file handle error.
    On the NFS server, create a new directory tree under NFS exported directory: 
    mkdir -p /home/exports/test/demo
    On the client, step into the directory: 
    cd /home/exports/test
ls
    On the NFS server, remove directory test with its subdirectory: 
    cd /home/exports
rm -rf test
    On the client, run 
    ls

    6. Finding the optimal write and read block sizes (wsize, rsize).
    Modify /etc/exports on the NFS server to allow root access to the exported directory on the client: 
    /home/exports  desktop02(rw,no_root_squash)
    Re-export the directory 
    /usr/sbin/exportfs -ra
    On the desktop, mount the directory with read and write block sizes option rsize=1024,wsize=1024: 
    mount -o rsize=1024,wsize=1024 node02:/home/exports /home/exports
    To make sure the directory is accessible, run command 
     ls -l /home/exports
    Check the time (real time) it would take to write 1.6 MB file over the NFS: 
    time dd if=/dev/zero of=/home/exports/testfile bs=16k count=100
    Check how long it would take to read this file: 
    time dd if=/home/exports/testfile of=/dev/null bs=16k
    Unmount the directory.
    Repeat the same procedure with rsize = wsize = 2048, 4096, 5125, 8192, 10240, block sizes (they are N*1024 Bytes).
    What is the optimal block size?

    7. Protecting portmap with tcp_wrappers.
    Unmount the NFS directory on the desktop. On the NFS server, put entry for portmap into /etc/hosts.deny: 
    portmap: ALL
    Try mounting the directory on the desktop. On the NFS server, in file /etc/hosts.allow, put entry allowing to mount the directory on your node: 
    portmap: 192.168.5.22

    8. Install autofs on the desktop machine (NFS client). 
    apt-get install autofs
    Configure the master map file, /etc/auto.master, and specify the timeout 60 seconds: 
    /mnt   /etc/auto.exports  --timeout=60
    Make sure directory /mnt already exists.

    Configure the indirect map file, /etc/auto.exports: 
    exports  -rw,hard,intr  node02:/home/exports

    Restart or reload autofs: 
    /etc/init.d/autofs restart

    Access the file system and check if it gets mounted: 
    cd /mnt/exports
df
    Run command df -h again after about a minute.



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